V i s i t o r   r e s p o n s e s 

R e :   E r n a g e   -   D e c e m b e r   1 1 ,   1 9 8 9   
 Received : 10/27/07  Estimates of size and distance - 1   Roger PAQUAY   

According to your web site, when the craft turned and moved in the direction of the witnesses, it was at a distance of 1 km (0.62 mile or 3,280 feet), a distance that can be measured on the scaled map. It is precisely that distance of 1 km which is interesting. In fact, I decided to verify the details of the case in VOB1 [the first tome of Vague d'OVNI sur la Belgique, published by SOBEPS in 1991]. On page 91, the witness is quoted as stating that the spotlight he observed when the craft approached had a diameter twice the diameter of the full moon. At that moment, only one big light was seen. This is very interesting as the apparent diameter of the moon is 30 minutes of arc, meaning that the spotlight was viewed under an angle of 1 degree of arc. Considering the distance, the spotlight would have measured 18 m (59 feet !!!), whereas the witness estimates that the three white lights that were seen at the bottom of the craft immediately thereafter were only 10 m (33 feet) apart.

Demonstration: tan 1° = 0.018; distance 1,000 m. In a right-angled triangle with a 1° angle we have: tan 1° = diameter spotlight/distance, or 0.018 = diameter spotlight / 1,000 or diameter spotlight = 0.018 x 1,000 = 18 m !!! A manifest exaggeration.

Waremme, Belgium

[Roger PAQUAY is a Belgian physicist and retired honorary director of a technical school. Mr. PAQUAY is currently drafting a book on the Belgian UFO wave in which estimates given by witnesses and investigators will be analysed mathematically.]

Our reply :

A spotlight of 18 m (59 feet) diameter does indeed seem huge, and although an object with an estimated size of 25 to 45 m could, at least theoretically, carry a lamp of such dimensions, the sketch Mr. A.A. made of the object seems to suggest a much smaller overall size. On this sketch, which we inserted in the lower half of our map of the sighting location, the mass behind the lights is represented by an irregular line drawn around the triangle formed by the three white lights. When we compare the size of this irregular shape with that of the equilateral triangle with sides of 10 m, the overall size of the object could not have been much bigger than 20 m.

In the light of Mr. PAQUAY's calculations, it would be interesting to know if (1) the irregular shape on the above-mentioned sketch can be considered a more or less accurate representation of the overall size of the object (assuming that, at some time during the sighting, the object blocked out part of the background giving the witnesses a clue as to its actual dimensions), and if (2) the spotlight Mr. A.A. and his wife observed, appeared bigger or smaller than the isosceles triangle formed by the three white lights.


 Received : 04/20/08  Helicopter noise - 1   Martin SHOUGH   

In this case, an Army officer, Lt. Col. AMOND [now retired], and his wife, stopped their car on what Wim [VAN UTRECHT] describes as a "lonely road" and wound down the window with "ears pricked" to try and detect any sound from an object of evidently large angular size showing details of lit "panels" or windows as well as various other separate lights which circled apparently nearby for up to 8 minutes. They heard nothing but "silence", even though the wind was from the S and the object approached them directly and at low level in the SSW. Wim concedes this but says:

"When the object executed the 360 degree turn, it was closer by and in the south-southwest. Under these circumstances one would expect that at least some of the noise had reached the couple. However, from his letter of December 19, we know that A.A. restarted the engine of the car immediately after the big light appeared. It is therefore conceivable that, during this phase, the sound of the car engine drowned the sound of the unidentified object".

I'm not sure that I follow the structure of this argument. Lt Col. AMOND said that they stopped the car, wound down the window and listened whilst the object was in the SSW performing its apparent 360 turn and continued listening when it seemed to bear down on them with its brilliant headlight. Only after this had happened did his wife urge him to restart the car, precisely because the object seemed to have approached. He then did so, and this action coincided with the end of this phase of the event:

"As I start the car again, the big light disappears and three white spotlights, less important than the preceding one, become visible... The object then actually performs a turn of 180 degrees to the left".

Was this an Army helicopter, perhaps a Puma or a Sea King, as Wim suggests? Lt. Col. AMOND does not think so and explicitly dismissed that suggestion in an early interview. Not only was there no sound but even with the light of a favourably-placed full moon illuminating the landscape and the object from behind the witnesses, no reflected shape or structure was visible at any time. Coming from a couple no doubt familiar with Army helicopters one feels inclined to give that opinion some weight; but it's true, as Wim says, that the main obstacle from our point of view is the silence. Wim also points out that there is evidence of a probable temperature inversion that night which could have reflected sound upward and away from the witnesses.

I looked at the radiosonde profiles. The De Bilt ascent [De Bilt is the most important weather station in The Netherlands, located 174 km N of Ernage] does show a very slight inversion above ~100 m developing through the afternoon, Idar-Oberstein inland [a German weather station 215 km ESE of Ernage] shows a more severe one in place somewhat higher by midnight. But is it really the case that an intervening inversion will deflect the sound propagation upwards away from the listeners? I don't think so. On the contrary, an anomalous lapse rate would tend to bend sound upwards and away from the witnesses. The sound waves will actually refract in the direction of cooler air, so an inversion will bend sound towards the ground not away from it.

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I can imagine that an inversion boundary having a very sharp gradient might tend to partially reflect some sound frequencies where the waves impinge on the layer at a shallow angle. The frequencies that might tend to reflect would be those whose wavelength is of the same order as the depth of the gradient layer. But analogously with partial reflection of EM waves, the bulk propagation would probably continue through the layer by refraction in the usual way, and the overall intensity near the ground may well still be enhanced by the inversion.

This needs to be taken up with experts on acoustics in the free atmosphere, but I'm suspicious of the theory as it stands, especially given the extreme efficiency required of this process in the case in question where two alert witnesses consciously optimised the conditions for the express purpose of detecting sound and heard none despite a favourable wind.

Does someone have a reference for a scientific discussion of this supposed sound-reflecting property of inversions?

Another effect that might be considered is noise cancelling by interference between direct and ground-reflected crests and nulls of the sound waves. Maybe such a thing can occur briefly by a rare chance. For it to persist for a long time I imagine we'd need a helicopter to fly at constant altitude over a perfectly flat and acoustically uniform reflecting surface in a curve of constant radius with the witness's ear at the exact focus - we could even say that this condition is approximated during the first 2 - 4 mins of the Ernage sighting. But of course this is the phase of the least sonic interest, since the car engine was running then anyway. It is later, when the car was stopped and the object was manoeuvring in the SSW, that the absence of sound becomes problematical. That such a cancellation effect should happen to occur then, and persist, whilst the helicopter is turning 360 deg and manoeuvring through changes of altitude and attitude, seems to me to be unlikely in the extreme.

Note also that the effect of the wind gradient should also have been favourable. This is the velocity gradient between the surface friction wind and the wind aloft which has the effect of refracting sound waves towards the ground in the downwind direction and away from the ground in the upwind direction. In this case at the very time when the car was stopped with the window open on the silent road and with the occupants' ears "pricked" the downward refraction due to an hypothetical temperature inversion would have been enhanced by the direction of the wind and by the downward refraction of sound waves due to the velocity gradient.

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A further factor is the shape of a helicopter's sound "footprint" which is sensitive to direction and flight aspect. From various web sources I find that in general the footprint tends to form an ellipse whose major axis extends ahead of the flight path. In other words because they were immobile and with the window wound down when the object approached them, this factor also favours the propagation of noise towards our witnesses just at the time when they are listening, and when the helicopter is closest to them, when it is upwind of them and when they are also getting the benefit of the wind gradient refraction. (The footprint seems to be extremely sensitive to the helicopter aspect because of main rotor pitch and tail rotor noise etc; but in any case, the circling manoeuvre of the helicopter at this point would expose the witnesses to 360 deg of the helicopter's noise emission.)

Of course these considerations can be minimised if the "helicopter" is far away. It's interesting to work out just how far away it could realistically have been based on the cardinal directions of the terminal sighting points and the rough estimated duration, which can?give us an estimated average angular rate and thereby places an upper bound on distance for a given average true ground speed. According to Lt. Col. AMOND the initial phase of motion from the NW to SSW (about 130 deg on Wim's map) took 2 - 4 min (the total sighting duration including the circling manoeuvre and recession being 5-8 min). This corresponds to an average angular rate of about 0.5 - 1.0 deg/sec. By translating a realistic helicopter ground speed to this angular rate we can then find a realistic limit for the distance of an hypothetical helicopter from the witnesses.

A fast attack helicopter like the Apache has a max speed of 365 km/h going balls-out, but a realistic speed in this situation is going to be the speed of a more typical general utility helicopter - and not max speed, but typical cruise speed, because after all we know the thing has to be turning at low level (supposedly slowing and circling to inspect a possible car in trouble according to Wim's scenario, so not in a panic to get somewhere) and we don't want the engine screaming and rotors roaring any more than they have to. The typical max rated speeds of such helicopters tend to to be in the region of 250 km/hr or about 135 kt, so let's assume a reasonable round figure of 100 kt in cruise then. We find that at this speed, for the bracketed duration estimated, the maximum bracketed distance away would be 1.5 - 3 nmi (2.75 - 5.5 km).

True distance would probably be less than this upper limit. Proximity is implied by Wim's hypothesis - a chopper crew reacts with curiosity/concern to the presence of the witnesses' stopped car, thus explaining the circling and approach with bright headlight followed by retreat when the car is restarted. There is other internal evidence that would rather strongly support this conclusion. The witnesses described seeing a series of four illuminated "panels" which in the helicopter hypothesis become windows on the side of the helicopter and several separate lights which become running lights and a red strobe on the fuselage. In other words a good deal of visual structure was reported implying significant angular size. The circular glare of the white "headlight" was alone estimated at some two moon diameters during the approach (of course this is not going to be an accurate measure of the size of a lamp housing but a subjective impression of the apparent size of the light halo, nevertheless it follows the trend of significant angular size).

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Could these discerned details be consistent with a helicopter at the maximum bracketed range found above, 2.75 - 5.5 km? Highly unlikely. Let's allow generously that the "windows" on the side of a big helicopter fuselage span 20ft - then they would subtend only 6 - 12 arcmin at this range, with divisions between the windows being only about 1.5 - 3 arcmin apart. Detecting this structure at all would be close to the limit of normal visual acuity for a 20/20 human eye, and already probably flatters the hypothesis considerably. If the windows in the rear of the chopper fuselage span only a more realistic 10 ft (we don't want a huge and thunderous Chinook remember, just a small and quiet-ish helicopter) then the figures are halved and become very implausible indeed - only a speck of light would be discernable.

These lines of argument are strengthened with Lt. Col. AMOND's statement that at closest approach the object dropped to an estimated 40 m altitude and was visible in front of the treeline to the SW (he tells us the landscape was well lit by the full moon), which Wim's page tells us was found to be 1500 m from the car. This would place the object in the order of 1 km distant, which is consistent with the reasonings above and is indeed very close to the distance shown in the map based on Lt. Col. AMOND's own drawings (and incidentally would also place a helicopter well below the altitude of the recorded temperature inversions that night).

So how loud ought a helicopter to have been? I found some measurements of helicopter noise made for different machines in different flight phases at different distances:

A SuperPuma approaching the measuring equipment somewhat off the line of sight (drifting over 70 deg of bearing) when at a slant range of 280 m it had a noise level of just over 83 dBA, and at 220 m it was over 85 dBA.

Using the inverse square law we can calculate that all else being equal this Super Puma at a distance of 2.75 km (plausible based on angular rate) would generate about 1/10^2 or 0.01 of this noise, or in the order of -20 dB down on the measured level, i.e about 64 dBA, and at the favoured shorter distance of 1 km would be 13 dB down or about 72 dBA...

Examples of some types of noise in this region of 60-70 dBA are average factory noise, a vacuum cleaner running a couple of metres from your ear, average-to-busy road traffic, conversation at one metre, a large transformer, a busy restaurant, or TV shows. At 80 dB are heavy city traffic within 10 m, loud-radio music or a garbage disposal machine.

This is a very crude procedure I admit, but these noises are maybe indicative of the sort of sound level that we require to be completely mitigated by our hypothetical inversion "partial reflection" effect or other possible noise-cancelling effect - despite the several other factors tending to favour audibility in the circumstances.

Strathconon, Scotland

Martin SHOUGH is the author of several articles and papers on UFOs and (alleged) radar detection thereof. He has compiled and evaluated an extensive catalogue of radar cases which forms the core of RADCAT, an exhaustive on-line resource presently under construction by Jan Aldrich and associates at Project 1947. SHOUGH has worked with Dr. David CLARKE on analyses of a number of UK military radar reports. He is a UK Research Associate for the National Aviation Reporting Center for Anomalous Phenomena - NARCAP, whose science director is Dr. Richard F. HAINES (see also our discussion of the 1990 Montreal case). Martin SHOUGH has worked on two major historical cases.

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Our reply :

The above reaction was posted on the EuroUFO list, an Internet forum created for long-time European UFO/UAP researchers (the web site of the European UFO Network can be found at Martin SHOUGH's comments provoked a lenghty debate on the forum in which several noted investigators were to participate. Reactions were also received from non-members of the EuroUfo list, including Lieutenant Colonel André AMOND himself and Major General Wilfried DE BROUWER who was Chief of the Operations Division of the Belgian Air Staff in 1989. An extensive digest of this debate is presented here.

In our reply to Martin SHOUGH we pointed out that our source for the sound-refracting properties of inversion layers was a brief instructions manual in which it was explained how helicopter pilots can reduce the noise of their craft. We found it on http:/ Unfortunately, this manual is no longer available at that URL. We do have a print though. What the manual tells us about sound and inversions is that "pilots should avoid flying under or in an inversion" because "an inversion layer has a tendency to 'bounce' the noise to the surface" (it is not sure whether the author used the term 'bounce' intentionally, or meant to say that sound waves refract (curve) when going through layers of different temperatures/densities). Anyway, we concluded from this that pilots who want to reduce the noise of their helicopters, should fly above an inversion layer so that part of the noise will be "bounced" upward. The question then was to find out if there was an inversion close enough to the ground for such a situation to occur.

For our web site article we relied on soundings from meteorological balloons released at Trappes (France), De Bilt (The Netherlands) and Idar-Oberstein (Germany). In addition, we consulted the synoptic data retrieved from nine Belgian weather stations surrounding the sighting location. Soundings from the station at Uccle (34 km NW of the sighting location), were not available when we visited the Brussels Royal Meteorological Institute, but thanks to Dutch investigator Frits WESTRA we now know that these data can be consulted at (the data from Uccle can be accessed by entering the station number, which is 06447). The data thus retrieved tell us that, at 01:00 am local time on December 12, 1989, i.e. 6 hrs and 15 min. after the sighting (the object was seen at approximately 6:45 pm), there were three inversions: one on the ground, one roughly between 1300 and 1900 m and one between 12,000 and 14,000 m (too high to be of any interest to us). These are the temperatures recorded at altitudes between 104 m (= station elevation) and 5,344 m:

104 m-3.1 deg
105 m -3.1 deg
382 m2.2 deg
1301 m-3.5 deg
1403 m-2.9 deg
1886 m0.0 deg
2941 m-6.5 deg
5344 m-21.7 deg

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Lt. Col. AMOND estimated that,at the beginning of the sighting, the unknown "craft" was at an altitude between 200 and 300 m. With the sighting location being approximately 160 m above sea level, this suggests that the object was flying just above the ground-based inversion layer. As such, part of the noise may have been refracted upward (possibly to be refracted downward again by the second layer and becoming "trapped" in between these two inversions). The bad thing is that there's a gap of more than six hours between the sighting and the soundings. In consequence, much of this remains guesswork. But perhaps the presence of a temperature inversion close to the ground is not so crucially important to explain the absence of sound. Even with no inversion present, it can be argued that the witnesses were located in what is referred to as the "shadow zone", a region that surrounds the upward curving waves and is free of noise (see illustration below gleaned from

temperature inversion

The synoptic data from the weather station at Gosselies,approximately 20 km WSW of Ernage, further tell us that, at 7:00 pm local time, there was a moderate to fresh breeze coming from the SSE. The object was in the west, so the wind may indeed have carried the sound away from the witnesses. The distance between the witnesses and the object (more than 1 km), and the fact that Mr. AMOND and his wife were inside a moving car, may also help explain why no sound was heard during the first minutes of the sighting.

So far so good, but the biggest problem of course is the phase during which the object made the turn and headed in the direction of the witnesses with the car now parked on the lonely road and one of the windows rolled down. In our web site article we rather quickly "solved" this problem by pointing out that it was at this moment that Lt. Col. AMOND restarted the car, meaning that, during that phase, the noise from the engine could have drowned a hypothetical sound coming from the unidentified object.

However, in his message of April 20, Martin rightfully points out that, according to the lieutenant-colonel, the car was started when the object was at its closest point, meaning that the noise of the car engine couldn't have drowned the sound of the object during the approach itself. So it seems like we have a problem here. Still, let's not forget that all this happened in a matter of seconds with the witnesses being overwhelmed with a feeling of anxiousness, and this from the moment the craft started to move in their direction.

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Many years ago the author of these lines had a rather terrifying encounter with a helicopter himself. The experience was powerful enough to convince him that the majority of close encounter cases mentioning "silent" objects with bright "searchlights" can be attributed to helicopters. The incident in question dates back to the early 1980s. It was described as follows in my reply to Martin SHOUGH on the EuroUFO forum :

"It was a calm evening with little or no wind. The sun had already set and I was walking on the narrow asphalt road that borders the Albert Channel (Albertkanaal) in the small village of Grobbendonk, Belgium. All at once, out of nowhere, a beam of light came from the sky and I found myself "trapped" in a cone of light. On the road and on the grass beside it was a very sharply delineated circular patch, about three or four metres across. I was standing in the middle of the circle and was terrified. I couldn't move and didn't hear a sound. It was only when the light went out and I looked around to see where it had gone, that I spotted a rather large helicopter in the distance, silhouetted against a part of the western sky that was illuminated by the streetlights of the nearby highway. Only at that moment did I hear a faint rotor sound. At no time had I felt any downdraft or heard any noise when the helicopter was straight above me. I never understood how that was possible, and the only explanation I could come up with is that I was in a sort of trance or dissociation by which the visual focus and emotional impact were so strong that they overrode the workings of the other senses (perhaps even affect my memory because I couldn't even remember having heard anything prior to the searchlight shining down on me). British UFO investigator Jenny RANDLES has coined the expression "the Oz factor" to describe this unusual state during a UFO close encounter. Others have invoked true UFOs mimicking helicopters (but forgetting to make noise). The same eerie impression of soundlessness also occurs during accidents : seconds before the car hits you (I'm drawing from personal experience again), all sounds seem to disappear, to only come back several seconds after you regain your senses. The effect is often used in movies, at times accompanied with slow motion images of the accident itself".

The biggest problem with this "emotional shock theory" is that Lt. Col. AMOND mentions explicitly that he "pricked his ears", something you would not normally do when in a state of dissociation. Could this have been just his way of emphasizing that absolutely nothing was heard?

Perusing the Internet for UFO reports mentioning silent UFOs that turned out to be a helicopter, we found only one such example (and not even a well-documented one). It can be found at (you need to scroll down to the sixth entry to find it). The report is in French and unfortunately no date is given. Below is an English (slightly edited) translation of the text.

"What can we say? We were on a trip by car in the area of Ypres, Belgium, when a blinding white light shone down on the car from above!! When we got out of the car, the light went out. No noise, except a dull sound. Then I saw a shape above us, I decided to follow this shape. I was thinking about a UFO and wanted to go to the bottom of this!! When I arrived at the army base at Ypres, I was speechless!!! An electric helicopter!! You can believe it or not but the helicopter was TOTALLY silent!! With its 3 lights, one in front and two at the back. All sorts of flying machines had crossed our minds, but we were dumbfounded because this helicopter didn't make any noise. It's true that our thoughts sometimes wander to unidentified flying objects, but now I had proof that this was not a UFO but this craft that hovered above us in silence!! Technology can be beautiful, but this scared the pants off of me!? "


 Received : 05/13/08  Helicopter noise - 2   Martin SHOUGH   

It is correct that an inversion will refract sound towards the surface, and the recommendation to avoid flying in an inversion makes sense therefore. But the inference that flying above the top of an inversion will have the inverse effect of abnormally refracting sound upward is unwarranted I think. The manual [see "Our reply" to Martin's previous mail] is recommending that you try to avoid unduly amplifying your helicopter noise for people on the ground, and that if you can avoid flying in inversions you can keep your ground noise footprint merely normal.

Normal sound propagation in a standard atmosphere has a small upward tendency because of the temperature/density lapse rate, which is what is referred to here, but that doesn't mean that flying machines are normally inaudible unless there is an abnormal atmosphere (inversion), just that sound waves launched horizontal will normally tend to rise a little - but of course not much of the sound energy is launched horizontally by (say) a helicopter: the net air momentum is shed very definitely in the downward direction and carries rotor and engine noise with it. Helicopters flying by are normally very audible (as I can tell you from frequent first hand experience with a variety of choppers on military exercises, mountain rescue operations/exercises and hydroelectric power-line surveys that make a pest of themselves in this glen, not to mention occasional air-ambulance helicopters that have been known to use a nearby flat pasture as the only practical landing spot).

In any case, if a helicopter was involved at Ernage, as I pointed out, there are several interlocking lines of evidence - latent and explicit - that suggest it must have been quite close and quite low, especially during the close approach upwind of the witnesses where it was reported against the backdrop of the moonlit trees at an altitude of only a few tens of metres. Such a helicopter could not have been above the top of the surface inversion recorded, which was at a few hundred metres (higher than 220 m AGL - we don't know where the actual top is, only that it is somewhere in the big gap between about 220 m and the next reading at ~1160 m AGL), and not very strong (compared with gradients that cause optical mirage for example, which tend to be many times as severe).

It's possible that the witnesses' guess of 2-300 m places the object above it during the start of the sighting. But this is a secondary matter. There's no evidence that flying above an inversion does more than help avoid intensifying the normal noise footprint. In fact even flying above an inversion would be expected to intensify that footprint above the normal for the reasons I discussed, though of course not by as much as flying within it.

Apart from the fact that this not the acoustically interesting phase of the sighting, I'd only note that specific quantities are probably the least reliable of things in witness descriptions of objects seen at night in the absence of valid distance cues. Much more reliable IMO is information latent in basic topological relationships, such as that an object was in front of A or behind B etc, where angles and distances of A or B can be physically determined afterwards. In this case that procedure applied to the most relevant portion of the sighting - when the object appeared nearest, upwind of the alert witnesses with motor off and window open - indicates an altitude of only a few tens of metres, i.e. order of 1/10 the height of the Uccle surface inversion. That isn't unarguable, but it is interesting.

I think it's worth emphasising that the witnesses noted, whilst driving, that they could not hear anything and took steps specifically designed to test the possibility that sound from the object was being drowned out: They stopped the vehicle, turned off the engine, opened the window and listened with "ears pricked". Their actions show that they thought about this possibility. They did have some expectation of being able to hear the object (i.e., had it been a familiar thing such as an Army helicopter) if conditions were right. And were the conditions in which they tested that expectation actually rather poor, by bad luck? No. We can show on the contrary that their own actions coincided with the external conditions for sound propagation in their direction becoming most favourable.

I also pointed out that all factors appear to conspire to enhance the conditions for audibility at this time. When the witnesses were listening, with the car engine off, the window open and their "ears pricked", the object was:

- upwind of the witnesses
- due South within about 20 deg of the SSE surface wind (Uccle wind at 280 m AGL was virtually due S, 00:00Z 12 Dec)
- at its lowest (according both to report details and to the "investigating a stopped car" helicopter scenario)
- at its nearest point to the witnesses
- approaching the witnesses (a typical helicopter noise footprint ellipse extends ahead of it)

Its noise carrying downwind would be enhanced by earthward refraction due to a temperature gradient inversion and further enhanced by the downward refraction of sound waves due to the wind velocity gradient

According to Lt. Col. AMOND he stopped the car so that the object, which had lagged behind on their right, now came abreast of them on their right. This was when they opened the window after 2-4 min. The object then continued past them on the right, heading SE. So this fly-past, and the entire 360° circling manoeuvre that followed, with the object between SSW and due S, took place with the car silent and the window open. These events account for at least half of the total estimated sighting duration of 5-8 min.

The story of your personal encounter with a near-silent helicopter (see "Our reply" to Martin's previous response) is very interesting. Evidently dissociative states such as you describe can occur, and in combination with special conditions unfavourable for sound propagation towards the witness, it makes sense that sometimes people can be surprised and misled by unnaturally quiet helicopters.

But considering all the factors I personally think it unlikely in this case, where conditions (so far as we can ascertain) appear to have been rather favourable for sound propagation, and where the witnesses' actions (more telling than merely subjective self-reports re state of mind) seem to me to indicate some presence of mind and alertness to the need to test initial impressions.

Strathconon, Scotland


 Received : 05/17/08  Helicopter noise - 3   Martin SHOUGH   

Re the Ernage case in particular and silent helicopters in general, I looked a bit further into the sound propagation question and helicopter noise sources. Perhaps this will help us decide the merits of the theory. Anyway I've collected some information for future reference - and just because it's interesting.

First, I wonder if the sound refraction diagram found by Wim [see the diagram in "Our reply" to Martin's message received 04/20/08], is too simplistic and possibly misleading for our purposes? Sound does not travel in "rays" like this of course (I realise we all know that). The rays are a device used to represent the wave normals of expanding wavefronts, and the shadow zone underneath the ray is also an idealisation. In practice I think the situation for an isotropic emitter is really more like this (sorry for rough sketch)

expanding wavefronts The ray diagram gives the impression of a clearly defined dead zone where no upward curving rays can go because they are intercepted by the ground, and some descriptions I've read also give this impression. But as far as I understand it the wave phenomena of diffraction, reflection, interference and scattering due to turbulence mean that it's much more complicated and that sound levels in the "shadow" are only ever partially attenuated from the free-field spherical (^1/2) loss.

Research in Austria by a Belgian university team (I didn't keep URLs for this source but we can google it), namely "Comparison of measurements and predictions of sound propagation in a valley-slope configuration in an inhomogeneous atmosphere", T. Van Renterghem and D. Botteldooren, Ghent University, P. Lercher, Medical University of Innsbruck, Austria found that:

"In the case of an upward refracting atmosphere, turbulent scattering into the acoustic shadow zone that is formed becomes important. Neglecting this effect often results in unrealistically large attenuations. (...) Based on experiments, it was found that the sound pressure level relative to free field propagation stays more or less constant in the acoustical shadow zone formed by an upward refracting atmosphere. This constant value depends on the geometry of the problem and on the strength of the turbulence. A value of -20 dB is common in acoustical literature. (...) [but] (...) The temperature profiles observed (...) contain upward and downward refracting parts [whose] influence ranges from -3 dBA to +10 dBA [+10 for the downward refracting parts]".

This was in a mountain valley where drainage winds and topography complicated the normal picture. As I understand it, the shadowing effect of upward refraction at distance from the source in temperature lapse conditions was mitigated (to only -3 dBA, which it's important to remember is a small difference in subjective loudness on the dBA scale, although it's 1/2 power on the normal dB scale) by the fact that the rising ground of the valley followed the refraction curve. Presumably the downward amplification was enhanced a few dBA by the same factor, but I don't find this to be very clear. Anyway it is clear that the refraction effects are generally only a few dBA, up to about 10 dBA.

That seems to fit with a similar study near Phoenix, Arizona. Arizona Transportation Research Center project SPR 555, "Evaluate the Atmospheric Effects Associated with Highway Noise Propagation" identifies 4 typical acoustic conditions that are well understood:

"(A) Uniform geometric spreading without any excess attenuation or amplification from refraction effects.
(B) Upward refraction creating an acoustic shadow zone with lower than normal sound levels. Sound levels with this condition will often be about 5 dB lower than for condition (A).
(C) Downward refraction creating an enhanced sound fields and higher than normal sound levels. Sound levels with this condition can be 5 to 10 dB higher than for condition (A).
(D) Sound focusing in localized regions. Depending on the amount of focusing, sound levels for this condition could be 15 to 20 dB higher than for condition (A) and more than 20 dB higher than for condition (B)

Note that the sound amplifications occurring in C and D (downward refraction by inversion and local focusing by more complex atmospheres) tend to be larger than the attenuation due to the shadow zone in B. This echoes the results found in the Austrian study (lapse attenuation -3 dBA; inversion amplification +10 dBA).

The Phoenix study found that in the local conditions at distances beyond a few hundred metres, where the effect of up- or down-refraction due to temperature gradients becomes significant, its contribution was typically limited at +/-10 dB.

So it would seem reasonable to infer that if there had been a fairly uniform temperature lapse at Ernage in fairly open level country it might be expected to cause an acoustic shadow where noise from a helicopter at ~1km is attenuated from (say) 70-80 dB down to somewhere in the range 60-70 dB, which is equivalent to about a doubling or halving of subjective loudness, though the log difference in power is much greater), perhaps more if conditions were just right. But attenuation from helicopter-like levels to anywhere near 0 dBA (the faintest normally detectable sound) just does not occur.

Anyway this is academic, because such a lapse condition, typical of a daytime atmosphere, is probably not the relevant one for Ernage.

Radiative cooling of the earth under a clear sky after sunset typically accompanies a change from lapse to inversion in the surface layer. This would be the normal tendency of the atmosphere. If we had no radiosonde data at all, an inverted gradient, or at least an isothermal gradient on the way to an inversion, would be our best guess. The measurements we do have support this.

As Wim says, it's unfortunate that the profile from De Bilt, the nearest ascent in terms of time, is not a useful profile above 188mAGL. Nevertheless within this surface layer the profile is that of an inversion (about 1.5°C/100 m) on top of an isothermal layer (i.e. averagely on the super-refractive side of neutral) and it looks very possible that this trend continues at least some distance into the unsampled 1230 m of overlying air. And there is evidence of general low level inversion conditions at each of the other stations Idar-Oberstein, Uccle & Essen. All of this leads one to think that a surface inversion would be likely at Ernage also.

So we should assume that some earthward refraction and amplification of sound is probable, not shadowing, and the crude figure of 70-80 dBA - based on the spherical-loss assumption - ought if anything to be a minimum, which would be enhanced further by favourable low level wind direction (light, but generally SSE according to Wim's synoptic chart - even SW/W at De Bilt within 15min of the sighting time) and small wind velocity gradients which were also generally favourable for downward refraction.

The only other factor (AFAIK) that we haven't yet considered is the attenuation by atmospheric absorption, which is proportional to temperature and inversely proportional to humidity. That is, warmer and drier air attenuates sound more effectively than cooler and moister air. This is why sound travels better at night when the air is cooler, and travels best of all at night in a damp atmosphere. So what about temp and humidity at Ernage?

The balloon station which is the closest to Ernage in terms of elevation above sea level is Essen only a few metres below Ernage (160 m) at 153 m. Surface temp here at midnight was +1.6°C, and the mean temp through the first three levels (330 m ascent) was +1.3°C. See temp figures for 4 stations tabulated below:

timesurf temp (°C)mean of 3 levels (°C)depth of 3 levels (m)
De Bilt418:00+3.4+3.8188
De Bilt400:00+0.6+0.3103
Idar-Ob.  37700:00-9.3-6.1145

Humidity figures (%RH) for the first 3 levels at the same 4 stations are:

LevelDe Bilt (18:00)De Bilt (00:00)UccleEssenIdar-Ob

These figures show that the air over the whole region was cold (close to freezing) and very humid (overall mean relative humidity 90%). Attenuation would be low. Sound propagation in these conditions should have been very good.

One other factor is sound frequency. Apparently much of the annoyance factor of chopper noise is the higher frequencies, which are most affected by atmospheric absorption, usually dropping off significantly beyond about 4-500 m. Higher frequencies occur mainly in the tail rotor, transmission and engine spectra. The attenuation of these high frequencies in particular will be minimal in the cold, humid air of Ernage.

Mid to low frequencies, coming mainly from the main rotor, go from the very low fundamental blade pass frequency (rate of blade rotation), which is in the order of 10 Hz, right across the spectrum of sensitivity of the human ear which has a peak at a few KHz. The ear is least sensitive to the lowest frequency parts, but this will be compensated somewhat because low frequency (long wave) sound is most susceptible to being amplified by down refraction. (In any case the published noise measurements are done in terms of A-weighted decibels, or dBA, which is a scale adjusted to compensate for the frequency spectrum of human sound response.)

Helicopter noise is highly directional. According to various sources, engine noise generally propagates vertically, much of it upwards. But the main components of the rotor noise - "thickness noise" (bulk air displacement by the rotor), "blade-vortex interaction" (BVI, when the advancing blade tip runs into the vortex shed from the previous plade tip) and "high-speed impulse" noise (HSI, which is the shock wave caused by the blade tip exceeding the speed of sound) - are projected into an ellipse extending predominantly forward and down (to a lesser extent rearward), and the vertical angle of peak noise occurs within a depression angle of about 15° from the helicopter nose.

All of which adds up to the following conclusions :

- a helicopter at lowish altitude approaching the Ernage witnesses (and to a lesser extent a helicopter receeding, during the circling and recession SW) has the sort of aspect, bearing and elevation most favourable for sound projection towards the witnesses;
- the atmospheric conditions of temperature, humidity and wind also appear to be most favourable for sound propagation;
- the witnesses arranged their own circumstances (engine off, window open, ears pricked) so as to be most favourable for sound detection.

Re the suggestion that the witnesses' own talking - or even shouting - could have drowned out the helicopter: The normal level of human conversation at 3 ft is about 65 dBA. It's even possible that they would have to be shouting to hear one another over the helicopter at an expected noise level in excess of 70 dBA. According to this "Helicopter Noise Analysis"

"U.S. Environmental Protection Agency guidelines for normal levels of voice effort and hearing ability at listener-speaker distances of about three feet (...) [show that] sentence intelligibility drops dramatically when the steady A-weighted sound level exceeds 65 dB. The following guidelines are conservative predictors of interference with conversation: Speech interference may occur outdoors when the sound level is 60 to 65 dB or higher (...) Speech interference may occur indoors, with windows open, when the outdoor sound level is 70 to 75 dB or higher. ...

HMMH obtained LAmax contours from the INM output for each aircraft type to examine the effects of the helicopter noise on normal speech intelligibility. Using the speech interference guidelines previously discussed, the 75-dB LAmax contours represent the area where the helicopters begin to interfere with normal communication levels indoors with windows closed for older construction not meeting current Title 25 requirements [i.e. presumably inside houses without double-glazing]. (...) levels normally exceed the 75-dB threshold along the route of flight when in level flight and when arriving and departing the helipad. Outside the 75-dB contour, the helicopter flight may potentially interfere with normal outdoor conversations. The arrival (from the east) tends to dominate the shape of the contour as the arriving helicopter has the 'blade-slap' effect and a shallower descent angle than the ascent angle on departure

BTW, "LAmax" represents individual peak noise events weighted for human audio frequency response, unlike some other time-averaged types of dBA measure that are used for various purposes. The whole dB/dBA thing can be very confusing and it isn't always clear what environmental and protocol variables have been factored in to certain measurements quoted, or what variables have been allowed for in comparisons of sound level. So I wouldn't be confident that my crude spherical-loss calculation of >70 dBA for a Super Puma approaching at 1 km is very accurate. An acoustics expert should really be consulted with all of this information - if anyone knows of one prepared to spend the time. But I think it's indicative and the trends of the environmental factors are probably reliable.

Hopefully some of this will be useful.

Strathconon, Scotland


 Received : 05/26/08  Estimates of size and distance - 2   Martin SHOUGH   

I'd like to point out that Mr. PAQUAY treats Lt. Col. AMOND's "2x moon diameter" light as relating to the angular size of a light source, when clearly this should be treated as an impression of the circle of glare (overloaded retina) caused by this "huge" and "brilliant" light shining into the witness's face. One would expect this to very considerably exaggerate the angular size of the source, and to convict Lt. Col. AMOND of inconsistency for implicitly estimating the object's lamp housing at 18 m across seems a little peculiar and literal-minded to me!

Moreover Mr. PAQUAY's calculation assumes 1 km at closest approach, which on grounds of angular rate and angular scale I calculated as being the likely order of distance for a helicopter during the bulk of the sighting and therefore a definite upper limit on the range at closest approach (perhaps more nearly half of this figure?).

Strathconon, Scotland


 Received : 06/05/08  A response from the prime witness   André AMOND, Col. (Ret.)   

1. Let me introduce myself: I am Colonel AMOND, Civil Engineer. I witnessed and reported a UFO sighting that you discuss on your site.

2. I would like to correct the approach of Mr. PAQUAY who claims that the observation of the "spotlight" was made while the craft was 1,000 m from my observation point. This is COMPLETELY WRONG. Indeed, at the moment the craft was closing in, its distance to my observation point was approximately 100 to 200 m. Hence, using the calculation method of Mr PAQUAY, the diameter of the APPARENT (not real) spotlight = 0.018 x 1000/10 to 5 = 1.80 m to 3.60 m.

3. Helicopter Issue. A loony assumption. Here is why I never mentioned it :

- That evening, no MANDATORY flight plans had been introduced and no helicopter flights took place (information provided by the BE HeadQuarters).
- The luminous panels (windows) of the craft were significantly larger than the windows of the Puma which have a parallel shape as opposed to those of the craft which were trapezium shaped in any relative position.
- The triangle formed by the lights was more equilateral than isosceles.
- The apparent size of the Main Spot at the nose (see paragraph 2) was significantly larger than the dimensions of the lights in a triangular configuration.
- The diameters of the spotlights of the craft were much larger than those of a Puma.
- NO noise from a craft that manoeuvres between 100 to 200 m and at an altitude of the same order of magnitude 50 m - 100 m. Forget the issue of temperature inversion, pure theory that plays no role at such short distances. Besides, how would that explain that I did hear a train pass at + or - 700 m and also the background noise of traffic on the N4 located at about 1 km?
- NO mass as shown on the images of the helicopters that you've photographed and which are on your site.
- Finally, being familiar with helicopters, I can assure you that, for a helicopter, it is impossible to manoeuvre at such a very slow speed and then at a very very fast speed at the end of the sighting like the craft did.
- In addition, there was no propeller wash or any other air turbulence created by the craft.

CONCLUSION : It’s curious to see how people develop a theory, or rather a story, based on unverified assumptions. This is not scientific at all.

AMOND André, Ir.
Colonel (Ret.)
Ernage, Belgium

Our reply :

We should first point out that the helicopter images in our picture galleries are not ours. As stated in the captions that accompany them, they are computer generated images from the SF movie Lost Voyage. As such they cannot be used for comparison with a real life event.

Essential in Col. AMOND’s mail however is the new distance estimation for the object’s closest approach, namely 100 to 200 m, whereas the initial SOBEPS account, published in both Vague d’OVNI sur la Belgique and in the April 1991 issue of Inforespace, suggests a distance in the order of 1 km for this phase (for a detailed discussion see "Our reply" to Prof. MEESSEN’s response of June 26, 2008).

Equally detrimental to the survival chances of our helicopter explanation is to know how literal one can take Mr. AMOND’s statement that no helicopter flights took place in the evening of December 11, 1989. This point was resolved in two messages from the then Chief of Staff of the Belgian Air Force Major-General Wilfried DE BROUWER, one received on June 22, 2008 the other on July 6, 2008).


 Received : 06/17/08  Estimates of size and distance - 3   Roger PAQUAY   

In his response, dated June 5, 2008, Col. AMOND claims that my distance estimation of 1,000 m for the phase during which the craft turned towards him is completely false and that the real distance at that moment was 100 to 200 m. He also disputes my calculations and qualifies them as unscientific.

With regard to the latter, this statement does not seem to be based on anything solid nor does Mr. AMOND present any evidence of it. As such, his opinion has no place in a scientific debate and is to be considered an ad hominem attack. In a scientific discussion, one can refute a statement by using solid arguments and scientific reasoning, not by unproven assertions. Considering his educational background as an engineer, Mr. AMOND knows very well that my calculations are not in dispute. Moreover, they initiated from data provided by himself shortly after the sighting. To claim now that the sighting occurred from a distance between 100 and 200 m is in total contradiction with the early data.

Considering the following two elements taken from Col. AMOND's statements, the calculations themselves cannot be disputed:

1. The spotlight had an apparent diameter of two times the diameter of the Moon.

2. The distance of 1,000 m was measured on a map drawn by Mr. AMOND shortly after the incident and published in Inforespace [the map-drawing mentioned by Mr. PAQUAY is the one that was also used for the map we included in our article. Later correspondence revealed that this map was not made by Mr. AMOND but by the SOBEPS investigator who interviewed Mr. AMOND - WVT]. This distance of 1,000 m equals the distance between Col. AMOND's point of observation and the centre of the circle executed by the object. I was able to verify this distance through comparison with another map, received from Col. AMOND on February 29, 2008, and for which map he specified that the side of one square measured 1,620 m. So I stick to this distance of 1,000 m, which corresponds logically to the phase where the craft turned toward him (note that during the second part of the turn, the spotlight was no longer directed towards the witnesses).

Ernage The map of the sighting location that served as a model for the illustration in our article and on which Mr. PAQUAY based his calculations. The map was published on p. 92 of Vague d’OVNI sur la Belgique and carries the indication "Figure 2.21". The black circle with the dot in the centre marks the spot where Col. AMOND parked his car. The black arrow shows the investigator’s representation of the path followed by the unknown object. Azimuth bearings are given but are barely visible on this print.

On May 26, 2008, Mr. Martin SHOUGH posted an attempted explanation for the excessive size of the spotlight on the EuroUFO list. He suggested that the diameter of two times the Moon's diameter was due to the blinding effect of a brilliant light shining into the witnesses' face. This "circle of glare (overloaded retina)" is believed to be the cause of the observed diameter.

This explanation does not satisfy me because :

1. The eye pupil reacts immediately to a brilliant or blinding light by reducing its diameter to at least one tenth of its initial diameter.

2. In a letter to the Cabinet of the Minister of Defense the lieutenant-colonel stated: "only an enormous spot of white light was visible now, bigger than the spotlight of a big aircraft carrier.

3. If Col. AMOND had been blinded by this brilliant light, he would not have been able to see clearly for 20 to 30 seconds, nor would he have been able to discern the three white lights and the red light which appeared immediately thereafter. Moreover, he never mentioned having been blinded.

4. In an e-mail I received from Col. AMOND on March 1, 2008, he stated : "The windows of the UFO had the same apparent size as the vertical size of the train carriages passing on the railway behind me when I stopped at my point of observation". He further added: "Luminous panels: white, light yellow. Light of the gyroscope or pulsing lamp: red. The colour of the three lights in a triangular configuration was white. The light of the big halo seen face on: white, non-directive, not blinding".

Another hypothesis could be put forward to explain this amazing result of an 18 m diameter spotlight. That explanation is the following : most observers typically overestimate the angular size of the Moon in the sky and this often with a factor of 20 to 50 and more. When you randomly ask someone to name an object that they believe would just cover the Moon when held at arm's length, the answer can be quite surprising. I quote a few examples: "a circle with a diameter of 10 cm" (20 times the Moon), "a CD" (12 cm across, i.e. 24 times the Moon) and "a soccer ball". In most people's minds, the Moon occupies a much more important amount of space on the celestial sphere than in reality. I persuaded a few of my acquaintances to test the experience themselves. They were amazed to find that an object about half a centimetre across suffices to cover the Moon. This overestimation of the Moon's size on the celestial dome is of course reflected in the overestimation of sizes of other objects that are compared to the Moon's diameter. Did Col. AMOND overestimate the size of the Moon and the craft? A number of elements in the lieutenant-colonel's statements and in the CLAV simulation [the computer animation made by the Centre Laique de l'Audiovisuel - WVT] converge to that interpretation. Let's study them in more depth.

In his e-mail of March 1, 2008, Col. AMOND writes : "The windows of the UFO had the same apparent size as the vertical size of the train carriages that passed on the railway behind me when I stopped at my point of observation".

According to a map sent to me by Mr. AMOND on February 28, 2008, the railway is 872 m away from the spot where the witnesses were. The height of a carriage is 4 m from the rails up. So one can calculate the angle b under which it should be visible at that distance. We get tg b = 4/872 = 0.004587, so b = 0.2628°, i.e. half the apparent diameter of the lunar disc, whereas considering the angular size of the windows on the simulation, if one agrees to their size being 1/3 of that of the trees, tg b = 2.86/3 or 0.954°, i.e. about two times the Moon.

In a mail dated March 28, 2008, I asked Col. AMOND the following question : "The spotlight seen face on, and which is said to have been twice the Moon's diameter, was it bigger or smaller than the triangle formed by the three lights, and to which extend?". By mail of March 29, 2008, the colonel replied as follows : "Triangle much bigger : 5 to 10 times".

So the apparent size of the spotlight (halo) is therefore comprised between 1 and 2 m, whereas comparison to the Moon's diameter yielded 18 m.

These different elements confirm an overestimation of the apparent diameter of the Moon and therefore also of the craft. This overestimation is automatically accompanied with an impression of closeness resulting in the underestimation of distances. In these conditions, impressions of speed and movement are falsified by the observer's conviction that he is dealing with an object at close range. In other words, there is confusion between apparent speed and real speed. This results in descriptions of movements, such as extremely tight turns, that would normally be impossible for man-made craft, but not when the observed objects are situated at their real distance. The absence of sound and the impossibility to see a structure behind the lights, also plead in favour of a greater distance, even more so since the Moon was shining at that moment.

So far my attempt at an explanation.

Waremme, Belgium
[Edited and translated from French by WVT.]


 Received : 06/22/08  Not a helicopter - 1   Wilfried DE BROUWER, Maj. Gen. (Ret.)   

The Belgian airspace is surveyed by four powerful radars, two military and two civilian, which are all interlinked, i.e. any duty controller can select the image of any of these radars at any one time. All radar registrations are recorded and these recordings are kept during a well determined period.

When the media reported the numerous UFO observations which occurred in the region of Eupen/Verviers on 29 November 1989, I asked to verify the radar recordings of all air traffic over the relevant area. Thorough analysis revealed that the observations were not attributable to any fixed-wing aircraft or helicopter. It should be noted that radars can track low flying helicopters, except when these are in a hovering position. In addition, the Civil Aviation (CAA) confirmed that no flight plans had been introduced to operate in the area. A flight plan is mandatory to fly between sunset and sunrise.

On 12 December 1989, I was informed by the secretary of Lieutenant Colonel André AMOND, who worked in the same building as me, that his boss had made an observation of an unusual craft in the area of Ernage (Gembloux). I asked for him to make a report and meanwhile verified whether this observation could have been caused by an aircraft. The answer was that no flight plans had been introduced and that none of the four Belgian radar stations had registered any traffic that could have caused this phenomenon. It should be noted that at that time, the Belgian armed forces and the federal police had only a few helicopters of the size mentioned by the sceptics, but these were stationed at more than 90 km from the point of observation.

Our conclusion was that we could not determine the nature or origin of the sighting.

A few days later, Lt. Col. AMOND sent his report to the Minister of Defence and I received a copy the same day. The cabinet (staff) of the minister called me and I informed them about the inquiry and findings of the Air Force.

André AMOND was later promoted to colonel and is now retired. Having heard about the critical comments made about his sighting, I went to talk to him and we reconstructed the event. I didn’t find any significant inconsistency between his 1989 report and his current version; only, he now made a more accurate and detailed sketch of the different phases of his observation.

Other point; his wife fully acknowledges their observation and remarked that, in 1985, after an exercise, her husband had been dropped by a helicopter in the back of their garden, approximately 80 m from their home. She remembered very well the terrible noise and the propeller wash; the whole village was alerted. Like her husband, she remains fully convinced : what they saw on 11 December was certainly not a helicopter.

Summarising, just like the other reported sightings of 29 November and 11 December 1989, the Ernage case cannot be attributed to a helicopter or any other aircraft. Discussions based on such assumption are not relevant. Furthermore, Colonel AMOND is a highly qualified and very reliable person, the major elements of his testimony are consistent and there is no reason why he should be discredited.

With my best regards,

Major General (Ret.)
Lubbeek, Belgium

[After spending twenty years as a fighter pilot, Wilfried DE BROUWER was appointed to the Strategic Planning Branch in NATO in 1983. As a Colonel, he became Wing Commander of the Belgian Air Force Transport Wing and, in 1989, chief of the Operations Division of the Air Staff. It was in this function that he was confronted with a massive wave of UFO reports. At a widely attended press conference, held at the NATO Headquarters in Brussels in the Summer of 1990, DE BROUWER revealed the details of what has since become known as the March 30-31 F-16 UFO chase. Promoted to Major General in 1991, he became Deputy Chief of Staff of the BAF, in charge of Operations, Planning and Human Resources. General DE BROUWER retired in 1995 and subsequently worked more than ten years as consultant in the United Nations to improve the UN logistics rapid response capabilities during emergencies. DE BROUWER lectured on the Belgian UFO sightings on several occasions, including the 2007 National Press Club Conference in Washington D.C. and the 2008 MUFON Symposium in San Jose, California.]


 Received : 06/23/08  Witness reliability - 1   Jean-Michel ABRASSART   

A little comment about the strawman argument at the end of Wilfried DE BROUWER's email:

"Summarising, just like the other reported sightings of 29 November and 11 December 1989, the Ernage case cannot be attributed to a helicopter or any other aircraft. Discussions based on such assumption are not relevant. Furthermore, Colonel AMOND is a highly qualified and very reliable person, the major elements of his testimony are consistent and there is no reason why he should be discredited.

I find it kind of annoying that UFO proponents can't seem to understand that, based on psychological and sociological researches, UFO skeptics say that EVERY human testimony is unreliable. There's nothing specific to one individual (here Col. AMOND). Human testimony is unreliable because we are human. Our perception, our memory, our recollection of an event and how we testify about it depend on the way our brains are hard-wired. To simplify this point : we see with our brains, so culture can influence they way we perceive things, no matter who we are. These influences can come from science-fiction or other UFO stories (in the case of an isolated UFO sighting), or media coverage (in the case of a UFO flap like the Belgian wave).

So it's a strawman to say that UFO skeptics try to "discredit" a person, when in fact we follow the scientific literature which tells us that every eyewitness testimony is unreliable.

No title (here colonel), and no qualification whatsoever, can make a human testimony reliable. We perceive an event subjectively, by definition. About the UFO phenomenon, the only thing I can think of that may help when observing an aerial phenomenon is to be an amateur astronomer. It will help someone recognise certain stimuli that lay people are not familiar with (meteorites and so on). But that doesn't imply that amateur astronomers can't be fooled by other stimuli (non astronomical ones) or cannot have hallucinations for example.

On top of that, Wilfried DE BROUWER writes that the colonel is a "very reliable person". This is a purely subjective statement on his part. It's not because someone is reliable in some situation (at work for example) that he is always reliable in every kind of situation. From a scientific viewpoint, assuming this is false too. That's not how we humans work. Seeing a UFO is not a usual situation at all. So, in my opinion, that kind of statement is meaningless, except if Wilfried DE BROUWER had presented us with an objective psychological personality profile of the witness to back up his claim, but I'm sure he didn't (and anyway, Mr. DE BROUWER is not a qualified psychologist). So, in the end it's like someone saying: "that person is a very reliable source because I talked to him on occasion and he seemed to act normal". As I said before, we can't infer from this that, in an unusual situation, that same person would be reliable as well.

Of course, all this has nothing to do with trying to discredit a specific person. The above is true for every human being, including me.

Yamaguchi, Japan

[Jean-Michel ABRASSART owns a degree in psychology and philosophy from the Catholic University of Louvain-la-Neuve, Belgium. He is also a member of "Comité Para", the Belgian French-speaking skeptic organization. In 2001 he wrote a thesis about the sociopsychological aspects of the UFO phenomenon. His main interest lies with the "predispositional and situational factors" that influence the belief in paranormal phenomena.

Jean-Michel currently resides in Japan where he works as an English teacher. He maintains his own blog, which has a section dedicated to the UFO phenomenon (]


 Received : 06/23/08  Witness reliability - 2   Grégory GUTIEREZ   

In my opinion, the important information in DE BROUWER's e-mail is not in his last paragraph about the reliability of Col. AMOND. Of course human testimony is not always reliable, but Jean-Michel ABRASSART tends to say that it’s NEVER reliable. I think he pushes his argument too far here, turning it into some kind of indisputable doctrine. After all, we're talking about a trained military man with already many years of service at the time of the sighting. I tend to believe that he would be more reliable than just any guy who is not accustomed to looking at flying machines in the sky, and was not informed about what was going on in Belgium in those days.

Anyway, I think what's important in DE BROUWER’s statement is the fact that, not only none of the four wide-range radars covering Belgium at that time detected a chopper in the area when the sighting occurred, but also that no chopper was registered to fly in that area on that day. This information tends to exclude two suggested explanations for this case and confirms that the unidentified object was not an "official" shopper with a flight plan for this day and time, and not an eventual "ghost" chopper that would have been secretly flying around with no flight plan (because it would also have been detected by these four radars).

Was it some kind of stealth chopper, unknown to the Belgium military network, flying over this area without authorization and able to hide from two civil radars and two military radars? This supposition too would have to be backed up with reliable facts or evidence (remember the funny Science & Vie article by journalist Bernard THOUANEL published during the wave and claiming that the F-117 stealth plane was responsible for the sightings).

I have no idea what was seen in the skies during the Belgium wave and I don't support any specific explanation, but I think DE BROUWER’s statement offers important and useful information on the matter.

Paris, France

[Grégory GUTIEREZ studied literature at the Sorbonne University in Paris. In 1998 he wrote a thesis on fantastic realism, a cultural movement that emerged in the 1960s after the publication of PAUWELS & BERGIER’s book Le matin des magiciens (published in English as The Morning of the Magicians). GUTIEREZ is also author of a book on the history of parapsychology (Les aventuriers de l’esprit - Une histoire de la parapsychologie, Presses du Châtelet, 2005) and his contributions have appeared in various journals that deal with anomalous phenomena, including the French Science Frontières and the British Fortean Times. From 2000 to 2006, he was a board member of the Institut Métapsychique International (IMI), an organization founded in 1919 to promote experimental research into "the rare and controversial capacities of the human mind". GUTIEREZ has worked on half a dozen web sites dealing with UFOs and parapsychology. His personal blog can be found at]


 Received : 06/23/08  Plasma stealth chopper - 1   Jean-Pierre PHARABOD   

Now I am beginning to wonder : how could it be that the four Belgian radars did not detect these objects in the sky which were neither aircraft nor helicopters. There is a futuristic, but not unphysical possibility : "plasma stealth". This was first mentioned in Russia in 1999, as an invention of Anatoliy KORTEYEV and his team (Keldysh Research Center), and subsequently studied in the USA and in France. See :

Jean-Pierre PHARABOD

[Jean-Pierre PHARABOD is a physicist and former research engineer at the French Centre National de la Recherche Scientifique (CNRS). He is the author of AVNI - Les armes volantes non identifyées (Editions Odile Jacob, 2000). PHARABOD also co-authored, with Bernard PIRE, Le rêve des physiciens (Editions Odile Jacob, 1993) and, with Sven ORTOLI, Le cantique des quantiques - Le monde existe-t-il ?]


 Received : 06/23/08  Not a helicopter - 2   Martin SHOUGH   

A very fascinating and valuable intervention from Maj. Gen. DE BROUWER.

Gen. DE BROUWER's first-hand testimony confirms not only that no helicopter should have been flying (as previously reported by Col. AMOND) but that, in point of fact, no illicit helicopter or other aircraft was detected by radars covering the area (two of them BAF/NATO and presumably displaying primary echoes in the ground environment as well as SSR transponder codes).

It has been objected (recently by Jean-Michel ABRASSART) that no human testimony is reliable, period. We have Gen. DE BROUWER's account but no contemporaneous documentary evidence (AFAIK). Certainly I am not in a position to prove Gen. DE BROUWER's statement that the radar picture was examined and a helicopter ruled out by a "thorough analysis", and to appeal to his position and qualifications may not be an absolutely impregnable position in strict logic. But in the real world I judge that if Gen. DE BROUWER had informed us either that:

a) an echo of a possible unidentified helicopter had been detected, or
b) that no thorough examination of the radar picture had actually been made at the time,

then the members of the EuroUFO list [where Gen. DE BROUWER’s response was first posted - WVT] would reasonably have accepted his testimony as highly significant. So, presumably, the gentleman's expertise and authority in this area (sceptical absolutism notwithstanding) have some value for us. Unless someone has documentary evidence otherwise.

Given this, and the previous difficulties encountered with the helicopter theory, I would like to propose to the participants in this debate that the theory should now be withdrawn as untenable (for all practical purposes) unless further specific evidence can be found. I suggest that attention should now be focused on other possibilities.

Is it possible to reach some kind of consensus about this?

Strathconon, Scotland

Our reply to Martin’s question can be found beneath the following response.


 Received : 06/26/08  Plasma stealth chopper - 2 / Map confusion   Prof. Auguste MEESSEN   

I will try to contribute to this debate by sharing with you that I have the following documents concerning the Ernage case:

(1) A "note" of 2 pages with an additional 3 pages of drawings sent by Ir. André AMOND, LtCol. BEM, to the Cabinet of the Minister of National Defence on December 19, 1989. This text was published in Inforespace No. 80 (April 1991) and in Vague d’OVNI sur la Begique (p.90-91).

(2) A standard SOBEPS questionnaire filled out by André AMOND on January 3, 1990.

(3) Another questionnaire filled out the same day by his wife.

(4) A detailed report compiled on January 9, 1990 by a mathematically minded investigator in the formal style of a SOBEPS rapport d’enquête. This report presents in a separate way what Col. AMOND told the investigator and what his wife told him. There appeared to be only one, but very instructive difference. Later more about that.

On June 17, 2008, J.P. PHARABOD asked if the published drawings on page 92 of VOB were made by Col. AMOND [this question from Jean-Pierre PHARABOD is not included in our visitor responses - WVT]. The answer is yes for the Figures 2.22a and b, as well as 2.23, but the map in Figure 2.21 has been slightly modified with respect to the original (the SOBEPS report contains the map that provided the basis for Figure 2.21). To avoid further possible confusions, I add a copy of this map to the present mail. I extract the following explanations from the report.

The Ernage case. The object was discovered by Col. André AMOND on December 11, 1989, at 18:45 in position 1 (surrounded on the map by a circle). The car of the witnesses was then in position A (surrounded on the map by a triangle). Actually, he saw only a row of four white-yellowish luminous trapezoidal surfaces of decreasing size and below them a nearly hemispherical red light of pulsating intensity. He saw no object that carried these lights, but they were moving with fixed positions relative to one another. They were slowly moving towards the south at very low altitude, and remained in view until they disappeared behind a row of trees near the farm of Sart-Ernage. These trees are presented as green dots on the map. Also indicated on the map is the azimuth which changed from 295° to 250°.

Ernage L.

The map that accompanied Prof. MEESSEN’s response. It appears to have been drawn by SOBEPS investigator J. LAURENT shortly after his interview with Col. AMOND. The map published in Vague d’OVNI sur la Belgique is an adapted version of this map. Distances and scale are respected, but in the book version several indications are blackened, probably for better reproduction. (WVT)

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Col. André AMOND was accompanied by his wife, who also saw the object at her right side immediately after her husband told her to look over there. It is important to note, however, that right from the beginning (in position A) she could discern a dark shape (une forme sombre), under which there was the pulsating red light. This difference can be attributed to the fact that the colonel was wearing coloured correcting glasses for far vision. His wife was not. The investigator noted in his report that the reactions of the witnesses clearly indicated that they had not deliberated in advance to tell the same story. Besides this difference, which proves that there was indeed an object, although dark and not easily recognized, everything fits well together.

I attach the sketch that Col. AMOND made of the ensemble of lights, i.e. when the object passed behind the two first trees. The trees were clearly visible at the horizon and had no leaves, since this happened in December. The colonel estimated the apparent height of the object as being about 2/3 the height of these trees. The object was thus very low above the horizon. Its apparent length was about equal to the separation of the two first trees, but its true distance was unknown. The colonel saw the light again when he arrived at B. Then he stopped at C, which is the highest point on this street. He stopped the engine, but did not extinguish the lights of the car. His wife opened the window at her side, and both witnesses continued to observe the phenomenon, which was still moving at the same altitude and at low velocity. The trajectory of the "object" can only be estimated, but it seemed to be linear and the object passed between two wooded areas (position 2).

Col. AMOND was astonished that he heard no sound coming from the object, although he pricked up his ears. He was also amazed by the fact that the light of the moon, which should have been reflected by the object, didn’t make it visible. The surface of the object remained dark and actually invisible to the colonel. The object moved from point 2 to 3 in about 3 to 4 minutes. When it arrived at 3, in front of the wood, which is indicated as a green patch on the accompanying map, it turned towards the car and directed a very luminous beam in its direction. Since the light became brighter and larger, the object came closer, but it remained lower than the tops of the trees behind it. The wife of the colonel became frightened and told him to start the car, which he did.

The car responded without any problem, but the object made a manoeuvre and raised, nose up. It distinctly showed its lower face now, but the colonel saw only three uniformly illuminated, white circular surfaces of equal diameter and a large circular, pulsating red light. The centres of the white lights seemed to form an equilateral triangle, but the dark surface of the object that carried them was oblique. The upper circular white light was (3 to 4 times) more intense than the two other circular white lights. At the centre of this triangle, there was the large red light that they had previously seen from the side. Its diameter was 2 to 3 times larger than the diameter of the white circles. The object then regained its previous position, so that the red light was again underneath. It then disappeared rapidly towards the south.

The diameter of the approaching light beam was very big (about two times the diameter of the Moon), but my personal opinion is that this doesn’t allow a determination of the diameter of its source. The light being too brilliant for that. The investigator writes that the light was "dazzling" ("éblouissant"). The actual distance at closest approach (between 4 and C) was also difficult to evaluate. Any calculations would thus lead to a pseudo-scientific precision, but subjective impressions should be recorded. According to Col. AMOND, the centres of the white lights were possibly separated from one another by 6 to 10 m. The actual values are not as important as the relative disposition of the four lights and the absence of sound, although the object had to be quite close and was flying at low altitude. During a reconstruction, the investigator used his chronometer to determine the total duration of the sighting. He found 10 minutes, but the phase during which the object approached with the dazzling beam in front and the one during which the bottom side appeared lasted respectively only about 30 seconds and 30-40 seconds. This description clearly excludes the helicopter hypothesis, invented by someone who was a priori convinced that this object shouldn’t be considered as a true UFO.

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Gen. DE BROUWER’s mail of June 22 provided important complementary information, since it stated that four powerful, interconnected radars didn’t detect anything that was flying there and specified that no conventional object was allowed to fly between sunset and sunrise. Since a moving helicopter would have been detected, even at low altitude, the conclusion of the investigations of the Belgian Air Force is that the Ernage case, as well as the other reported sightings of November 29 and December 11, 1989, "cannot be attributed to a helicopter or any other aircraft." Gen. DE BROUWER adds that "Colonel AMOND is a highly qualified and very reliable person, the major elements of his testimony are consistent and there is no reason why he should be discredited."

J.M. ABRASSART reacted (on 23/6) in a rather astonishing way. He finds it "annoying" that UFO proponents don’t understand that "UFO skeptics say that EVERY human testimony is unreliable". Mr. ABRASSART adds that "There is nothing specific to one individual" that "DE BROUWER is not a qualified psychologist" and that "the scientific literature tells us that every human testimony is unreliable, no matter who we are." This is an extraordinary claim, requiring extraordinary proof. Grégory GUTIEREZ responded (the same day) by saying that, although human testimony is not always reliable, to assert that "it’s NEVER reliable" is pushing the argument too far. Martin SHOUGH concluded (also the same day) that given the lack of proof "and the previous difficulties encountered with the helicopter theory, I would like to propose (...) that the theory should now be withdrawn as untenable (for all practical purposes) unless further specific evidence can be found". "I suggest that attention should be focused on other possibilities", Mr. SHOUGH added.

I certainly agree that it is necessary to sort out unrealistic claims, but that doesn’t mean that all UFO sightings have to be discarded and that all witnesses are unreliable. Martin SHOUGH wrote (also on June 23) that "science cannot be allowed to rule human experience out of consideration" and "à propos Ernage, it would be perverse to claim that an army Col.'s familiarity with helicopters is irrelevant to assessing his certainty that he did not see a helicopter. Witnesses are imperfect measuring instruments, but it remains possible that as a group their reports may contain information about physical phenomena with which we are ourselves unfamiliar". He provided more reflections that are pertinent for our discussion, and noted in particular that an asymmetric treatment of human testimony, attributing higher weights to observations that are in favor of the privileged hypothesis and "zero weighting" to those that yield opposite results, simply isn't objective".

Jean-Pierre PHARABOD noted (that same day) that "Now I am beginning to wonder: how could it be that the 4 Belgian radars did not detect these objects in the sky which were neither aircraft nor helicopters? There is a futuristic, but not unphysical possibility: plasma stealth". He provides a very interesting reference in this regard. I have to add that the main result of my investigation of radar detection during the Belgian UFO flap was that we can be sure that it is extremely difficult to detect these objects through the scattering of microwaves. Some kind of stealth technology had to be involved. The problem of making ships and aircraft undetectable by means of sound and EM waves (visible light, infrared light or microwaves) is extremely important for military engineers (see "Invisibility rules the waves", Physics World, March 2008).

I got interested already some years ago in searching a physical explanation of the fact that some UFOs seem to have the capacity to make themselves optically invisible. I spoke on the phone with a German military pilot who, in the seventies, while flying his star-fighter jet (F-104G), made three "interceptions" of the same UFO. They did correspond to a frontal approach, so that the UFO passed the plane at very close range. He always had a clear radar image, but he never saw the object. The ground radar was also unable to detect it. The airborne radar was not yet of the Doppler-type, but it tracked the object in a continuous and coherent way. Since stealth technology of radar waves can already be realized by using flat surfaces and absorbing paint, the really new feature results from the apparent capacity to become optically invisible. Some authors mentioned in the UFO literature that occasionally, these objects can change their form or seem to appear or disappear where they are, as if they had the capacity to materialize or dematerialize. Allen HYNEK mentioned a case where the disappearance was progressive (like the Cheshire cat in Alice in Wonderland). I also heard of a stationary UFO that disappeared, as if it was moving a veil in front of it.

A single observation of this type would be unimportant, but a group would raise a question concerning the underlying technology. We should then try to find out a possible explanation. Is it possible to modify the refractive index in the vicinity of the object, so that light rays are deviated in such a way that they bypass the object by resuming their initial directions of propagation, as if no object had been there? There may be other possibilities as well. Anyway, the Ernage case is not the only one where the actual object was not easily detected by the naked eye.

Hamme-Mille, Belgium

[Auguste MEESSEN studied at the Science Faculty of the Catholic University of Louvain (UCL), Louvain-la-Neuve, Belgium. From 1960 till 1962, he was a research associate at the U.S. Massachusetts Institute of Technology. After that, he became a professor at UCL, where he teached quantum mechanics, theoretical and mathematical physics, solid state physics and didactics of physics. He became a professor emeritus in 1996 and continued to do research in various fields. Prof. MEESSEN, now retired, was also an important member of the Brussels UFO group SOBEPS. His personal web site with numerous papers on the UFO subject can be found at]

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Our reply :

Following Gen. Wilfried DE BROUWER’s reaction of June 22, Martin SHOUGH asked (on June 23) if it would be possible to reach a consensus and focus on explanations other than the helicopter theory. In principle that would be okay for us, but we think that to abandon the theory altogether at this point, as Gen. DE BROUWER and Prof. MEESSEN suggest, would be a mistake.

Let’s not forget that, despite the damage already inflicted on the helicopter theory, several of the reasons why we proposed this explanation in the first place still remain intact. First there is the general aspect of the reported object, and in particular the luminous panels (which can be interpreted as windows), the white lights and the pulsating red light (which are typical of normal aircraft), and the bright light in front of the object (which strongly resembles a helicopter searchlight). Secondly, there is the manoeuvrability of the object, and in particular the almost complete turn close to the ground which a helicopter is perfectly capable of executing.

Apart from the general aspect of the unknown object, our personal experience with a "silent" helicopter (described in "Our reply" to Martin SHOUGH’s response received on April 20), and the fact that our country went through a UFO hype at the moment (causing many people to report ordinary aircraft as UFOs), we had noticed that helicopters were barely mentioned in the official statements issued by the BAF about the Belgian UFOs. Also, ufologists and sceptics alike had never taken any action in this regard. And finally, our own efforts to try to find out if helicopters could have been responsible for some of the key sightings had produced nothing either (letters to pilots were left unanswered and e-mails to the Army’s information services suffered the same fate).

In November 1996, CAELESTIA’s photo and film analyst Jan VAN EETVELT asked us to prepare the draft of a Parliamentary question which his father, Representative Jozef VAN EETVELT, would be prepared to address to Mr. PONCELET, our country’s Minister of Defence at the time. We readily agreed and thought it would be a good idea to include a question about an incident which had occurred some 7 hours after Col. AMOND’s sighting in a village called Jupille-sur-Meuse, close to Liège. More specifically, we asked if the Defence Minister had any information that could help elucidate this spectacular incident (a helicopter and military personnel were said to have visited the area the day after). The response was somewhat different from the reaction we received from Gen. DE BROUWER on June 22. This is what our Minister of Defence stipulated with regard to the sightings that occurred between December 2 and 18, 1989 (we translate from French):

"After examination, it is impossible to make a correlation between the visual sightings and certain parasite radar echoes that are often generated by thermal inversion. This inversion was present during most of the sightings. (...) When flying at night, VFR flights [Visual Flying Rules - WVT] are only authorized for helicopters. Other airborne vehicles are obliged to introduce a flight plan according to the IFR (Instrument Flying Rules)".

Apart from this last sentence there was no mention of helicopters in the Minister’s reply (the rest of the text focused mainly on the F-117A, RPV, ULM and AWACS aircraft).

On December 8, 2002, in an attempt to help French investigator Renaud LECLET with a paper he was preparing on the Belgian UFOs and helicopters, we decided to send a letter to Gen. DE BROUWER asking him if there was still a way to find out if there had been a helicopter in the air during the night of Col. AMOND’s sighting. We never got a reply.

So, by 2003 there was still nothing conclusive that allowed us to rule out the presence of a helicopter in the southern part of the country on the night of December 11-12, 1989. Convinced that everything possible had been done, Renauld LECLET decided not to wait any longer and to include the Ernage incident in his analyses of the Belgian wave. In his text, he supported the idea that the object seen by the colonel and his wife had been an army helicopter. Renaud then tragically passed away. Four years later, I published a summary of the case on the CAELESTIA website, hoping it would finally produce some useful feedback.

When in October 2007 Roger PAQUAY’s calculations suggested that Mr. AMOND had underestimated the distance to the object and overestimated the object’s size, the helicopter explanation seemed even more solid. However, in April 2008, the theory suddenly lost ground when Martin SHOUGH reacted on this forum with an elaborate series of notes on helicopters and sound propagation.

Now, in June 2008, two new statements have been made that seem to torpedo the helicopter theory once and for all : one by Col. AMOND himself, stating that, at one point during the sighting, the unidentified object was only 100 to 200 m away from his car, and another from Gen. Wilfried DE BROUWER, stating that no helicopters were in the air that night. But before we are prepared to put the theory to rest, we would like to see some points cleared up first.

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(1) Regarding Col. AMOND’s claim that the object came to within 100 to 200 m of the car

Mr. PAQUAY based his calculations on the map that accompanied our article. This map is a stylized, but loyal, version of a map published on p. 92 of Vague d’OVNI sur la Belgique, where it is labelled as Fig. 2.21. Drawn on this map is the presumed path followed by the object. Since the path is drawn on a scaled, printed map, we assumed it to be accurate. Measured on this map, the object appears to have come within a distance of about 830 m from the parked car (Mr. PAQUAY used a distance of 1,000 m, i.e. the approximate distance from the car to the centre of the circular path).

However, on June 5, Mr. AMOND stated that the object came to within 100 to 200 m of the car, not 1,000 m.

Following this statement, we pointed out to Col. AMOND (on June 13) that the distance he now mentioned was not corroborated with the object’s flight path as indicated on Fig. 2.21. On June 15, Mr. AMOND replied, that this map was "absolutely NOT accurate". To emphasize this, Col. AMOND send us a PowerPoint presentation (a link to an updated version can be found further down this text) with on p. 2 the map in question accompanied by the following comments :

"Free-hand sketch provided in 1989 for:
1. General Information
2. Idea of the geographic places (between ERNAGE and GEMBLOUX)
3. Description of the different stages
 - Sketch NOT accurate at all
 - Made out of mind
 - Without going into details
 - Map support NOT correct".

As the discussion unfolded it became clear that Col. AMOND had placed the wrong map next to the above quoted text and that, probably, he had another sketch in mind, namely Fig. 2.23 in the SOBEPS book. This illustration is indeed a free-hand sketch made from memory and without the help of a map. It’s obvious that such a sketch cannot be used for measuring distances.

But what then with the much more detailed Fig. 2.21, the one we used for our web site article? Was it accurate or not?

From Prof. MEESSEN’s response we understand that Fig. 2.21 was based on a map drawn by SOBEPS investigator J. LAURENT shortly after his interview with the two witnesses. Like Figure 2.21, this early document (published above) shows community boundaries, printed titles, and much detail. The object’s trajectory appears to have been carefully drawn and azimuth bearings are included for different phases of the observation. If we are to measure the closest distance between the car and the unknown object on this original document, we get 800 m, which is close to 830 m, but still very different from "100 to 200 m".

Yet, even with regard to this map, which indirectly also formed the basis for Mr. PAQUAY’s calculations, Col. AMOND now tells us (via an e-mail received on July 4), that this map too is ?NOT accurate? and that the details in the SOBEPS report that deal with distance, altitude, trajectory and size do not tally with the information he provided to the SOBEPS investigator. This is odd because we have rarely seen a UFO investigative report with a more detailed map than the one provided by Mr. LAURENT. Prof. MEESSEN seems to be taking our side on this, since he explicitly tells us that this map is "very detailed" and "compiled by a mathematically-minded investigator". Also, this must be the first time in history that a UFO investigator places the reported UFO at a greater distance than the witnesses believed it was.

On June 18, Col. AMOND sent us a new version of his PowerPoint presentation. Fig. 2.21 is still there (along with the erroneous caption) but added is a page 8 with a panoramic view of the sighting location photographed from the spot where the car was parked. Indicated on the photo is the path followed by the object as seen from the car. It confirms that the object emerged from behind a block of trees and then descended below the tree tops of another group of trees and turned towards the witnesses (there was a temporal confusion about this too). More importantly however, the PPT also includes a new map. This time the object’s flight path is traced on a Google Earth map. Surprisingly, the circular part of the trajectory now stretches to within only 80 to 100 m of the parked car...

By way of comparison we made the following illustration showing the presumed flight path as drawn by the SOBEPS investigator in early 1990 (blue arrow) next to the flight path as presented in Col. AMOND’s recent PowerPoint presentation (yellow arrow). The position where the car was parked is marked with a red "x". Measured on this Google Earth map, the distance between this spot and the point of closest approach is 800 m on the 1990 SOBEPS map, and only about 100 m on Col. AMOND's recent PPT map.

Ernage (Google Earth)

In the light of these conflicting estimates, it is unfair to label Mr. PAQUAY's calculations "pseudo scientific". All Mr. PAQUAY did was rely on the best available evidence, namely the map we published and which was based on a carefully executed and detailed drawing made by a (mathematically-minded) investigator shortly after the event. When 18 years later, one of the witnesses offers previously unpublished estimates that suggest a much more spectacular "close encounter", it is only normal that reservations are being made.

There can be only one conclusion from all this, namely that there is no certainty about the distance of the object when it completed the 270° turn. All we know is that, at a given moment, the object descended in front of a block of trees in the background that is located at 1,400 m from the spot where Col. AMOND stopped the car.

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(2) Regarding Gen. DE BROUWER’s statement that "none of the four Belgian radar stations had registered any traffic that could have caused this phenomenon"

The way this sentence is phrased makes it essentially meaningless as it still doesn’t tell us whether or not a helicopter or a small airplane had appeared on the radar screens at the time of the sightings. From Gen. DE BROUWER’s statement, one is inclined to infer that traffic was registered, but that the person who verified the registrations didn’t think this traffic had anything to do with the reported UFOs. If that was indeed the case, we for one would like to know what was registered exactly and why it was considered irrelevant in explaining the reported phenomena. Was it because the radar returns were easily identified as ordinary aircraft, because they appeared too far away from the UFO hot spots, or because they were identified as irrelevant "parasite radar echoes" caused by a thermal inversion, as mentioned in the response to our Parliamentary question quoted above?

But there’s another reason why we are reluctant to put the matter to rest.

Gen. DE BROUWER claims that no aircraft were in the air, not in the evening of December 11 and not in the evening of November 29, 1989 (the day the Belgian wave began). Yet, Mr. PAQUAY himself informed us that, on November 29, 1989, he and his son were standing on the second floor of the hospital at Seraing, near Liège, when both saw how several Mirage jets were flying on and off the air base of Bierset (Bierset being 7 km NNW of Seraing and 41 km west of Eupen city where the majority of November reports emanated from). This happened shortly after 5 p.m. on November 29, 1989. The jet planes first headed southwest (following the orientation of the landing strip), then turned to the hospital with the white light on the front landing gear clearly visible, and finally executed a large circle. Two hours later, just before 7 p.m., Mr. PAQUAY was on a road near Hognoul (4.5 km N of Bierset) when two Mirage jets passed at low altitude over his car. He could clearly see their typical triangular shape and the flashing lights on the wingtips. The jets were flying towards the north-northeast and it would have taken them only 5 minutes from Hognoul to Eupen. Was Gen. DE BROUWER informed of these flights? Were they not mentioned because they were thought to be irrelevant?

So we’re still not entirely sure whether we should abandon the helicopter theory completely (personally, I would rather store it in the fridge for a while). Still, our reservations should not keep us from examining other possibilities, and we agree with Jean-Pierre PHARABOD that, in doing so, we should also take into consideration the other reports collected for December 11-12.


 Received : 07/02/08  Recapitulating   Martin SHOUGH   

Re your reply to Prof. MEESSEN, you're right, the statement about flight plans in the Defence Minister’s reply to the Parliamentary question is different from what we understood Gen. DE BROUWER to say. It's hard to find reliable information about airspace regulations in 1989 because new ICAO [International Civil Aviation Organization - WVT] conventions appear to have come in during 1990, but certainly the situation since then would seem to support the Minister in one important respect : VFR [Visual Flight Rules - WVT] helicopters in a Class G airspace or earlier equivalent (uncontrolled, below a few hundred metres and not near an airport), which this probably was, would not have been subject to ATC [Air Technical Control - WVT] clearance. No flight plan required (assuming they intended to stay in that space).

Since 1990, though, it would not be correct to say that helicopters are especially exempt in this way - any aircraft operation within the airspace is covered by the ICAO regulations pertaining to that airspace. But perhaps the Minister's statement was exact in 1989?

I think the issue of the maps and distance estimates has already been turned inside-out and upside-down. Recent "memories" about distances that could not have been reliably known in the first place, and which have no provenance in the case record, have low weight and new arguments based on them can only prompt further rationalisations and confusions.

I tend to agree that qualifying Mr. PAQUAY’s calculations as "pseudo scientific" is an unnecessary and not very amicable insult, but I don't think that the suggested inconsistency in the apparent size of the light is very material, as discussed in detail elsewhere.

As regards the distance issue, this has been approached in an early post from two different directions - angular size of resolved details and angular rate - and on these grounds it was proposed that consistency with helicopter speed and size could be argued if the distance of the helicopter during the first phase of the sighting was about 1km or so. Of course errors can arise with the timing, but less so with the angular size argument owing to the rather well-defined limits of human visual acuity, and these two lines of argument (if I recall correctly) tended to converge. This is fairly consistent with the map path as originally drawn in VOB [Vague d’OVNI sur la Belgique - WVT] figure 2.21. A path including a descending circular turn towards the witnesses, dropping below the tree line (backstop distance ~1500 m according to the original scale)would then tend to bring a helicopter within a few hundred metres. This then becomes problematic on the grounds of the silence (for all the detailed reasons previously adduced).

If the UFO was an unidentified VFR helicopter staying low underneath controlled airspace then maybe ATC wouldn't have known about it, and, as you say, perhaps helicopters were not at the forefront of people's minds so it did not occur to DE BROUWER or anyone else. But in that case a radar track meandering around Sart Ernage that was not recognised as a helicopter would have been seen as confirmation of Col. AMOND's "UFO" and we would presumably have heard about it from DE BROUWER. Ergo, if there were any unrecognised VFR helicopter "UFOs" tracked Belgian radars that night they presumably did not fit the place and time of the sighting.

Re your reply to Prof. MEESSEN’s response, storing the helicopter theory in the "fridge" sounds good. I completely agree with all of that.

Strathconon, Scotland


 Received : 07/03/08  Estimates of size and distance - 4   Martin SHOUGH   

Thanks for Mr. PAQUAY's follow-up. I was not (as Mr. PAQUAY believes) suggesting that Col. AMOND was "dazzled" to explain a large image. As he says, an "overloaded retina" is not a very good explanation. Rather I was suggesting that the impression of the size of the light owed much to another common intra-ocular effect, a diffraction corona, vide:

"when a brilliant light is shone straight into your face it is scarcely possible to estimate the size of the source inside the glare halo or so-called ciliary corona. This glare is due to coronal diffraction caused by particles in the fluid of the eye and produces a disc of brilliance that is actually composed of a dense array of radial spectra. It can be measured. Experiments with a small halogen lamp (filament 1.8 x 1.0-mm) located 4 meters from the subject against a black background found that the mean reported ciliary corona diameter for a range of eye conditions was 8 degrees".

The average intensity of the corona is less than the core intensity of the source, reducing radially. It is not necessary to assume a disabling saturation of photoreceptors over a large area of retina, even if some afterimage would not be at all surprising.

More generally I would like to insist that we are only talking about subjective impressions, and I don't consider that "twice the size of the moon" can be taken too seriously, partly for the reasons which Mr. PAQUAY sets out - angular estimates are routinely exaggerated and the mental calibrations involved in comparing exaggerated subjective impressions of two dissimilar visual objects not present simultaneously in the same field of view are difficult to work out - to say the least!

Yes, gross overestimation of the moon diameter in memory is the norm; so when someone says an object is twice the size of how they think the moon ought to look they are actually factoring into their report an underestimate of the true angular size, because in fact it might have been many times the true angular size of the moon. But the relationships between perceived angular size and perceived physical size/distance in cue-reduced conditions are I think very subtle, reflecting many factors including mental set, and have inter-dependent values rather than being fixed factors plugged into a linear "calculation". One can also argue in this vein that if Col. AMOND thought the object was much closer than it really was, then his estimate of intrinsic brightness (far brighter than a familiar helicopter searchlight in comparable circumstances) is too conservative. How does this play into his impression of angular size?

It's true the moon was available in the opposite part of the sky for indirect calibration, rather like the train windows; but honestly I see no solid ground under this sort of exercise. It seems safest just to say that it was "a huge light" that seemed (to an "expert witness") far too big and bright to be on a conventional aircraft, but acknowledge that the subjectivity can't be removed.

Strathconon, Scotland


 Received : 07/06/08  Not a helicopter - 3   Wilfried DE BROUWER, Maj. Gen. (Ret.)   

Dear Mr. Van Utrecht

Allow me to clarify a few points.

1. Your statement: "A helicopter is perfectly capable of executing such a manoeuvre".

The report of André AMOND suggests that the object was making a tight turn with a considerable angle of bank (45 degrees?) at very slow speed (20-30 km/h?).

When hovering or flying at such a slow speed, a helicopter has to keep its main propeller horizontal. Indeed, the lift vector should remain opposite to the gravity vector because it cannot generate any lift from the forward speed. If performing a turn at such a slow speed, it should keep the propeller as much as possible in the horizontal plane, using the rudder to action the tail rotor to make the turn. As such it will not take any significant bank; otherwise it would fall out of the sky. In other words, the manoeuvre as described by Col. AMOND cannot be performed by a helicopter.

2. Regarding your close encounter with a helicopter [see "Our reply" to Martin SHOUGH’s response received April 20, 2008 - WVU]; during my 39 years in the Air Force, I experienced at least one hundred close encounters. Even after my active flying carrier, in Feb/Mar/April 2000, I was in charge of up to 25 helicopters, including not less than 10 Oryx/Pumas, performing rescue and relief operations during the flooding in Mozambique. I never experienced a helicopter approaching me without making any noise. On the contrary, in most cases, the noise of the propellers is heard before the helicopter is visually spotted.

3. Helicopters were not often mentioned in the BAF reports because they figure under the term "aircraft". Do you really think that we were stupid enough not to consider the helicopter option? At that time, the Air Force had 500 pilots, 300 engineers, 100 air traffic controllers, etc. and, believe it or not; some of them have brains. We were desperate to find an answer regarding the Nov 29 and Dec 11 sightings but, unfortunately, we didn’t.

4. Regarding the second part of the answer to the parliamentary question to the Minister of Defence:

"When flying at night, VFR flights [Visual Flying Rules - WVT] are only authorized for helicopters. Other airborne vehicles are obliged to introduce a flight plan according to the IFR (Instrument Flying Rules".

Indeed, I could have been more explicit but I wanted to make a short statement without going into details. Normally flight plans are introduced before take off but, for urgent cases, it is possible to introduce them once in the air. In 1989, in some cases, helicopters were allowed to fly VFR without a preceding flight plan; more precisely in case of military exercises and in emergencies.

- In case of military exercise, helicopters can be given a blanket authorization to operate within a well determined zone. The evenings of Nov 29 and Dec 11, no exercises took place.

- In case of emergency; Search and Rescue, Police and Ambulance helicopters were authorized to take off without previous authorization. Please note that ambulance helicopters were not common in 1989.

Nevertheless, in both cases, once in the air, the pilot has to contact the relevant airspace information/surveillance/controlling authority and communicate the point of departure, point of arrival, intentions, etc. In other words, depending on the case, the military and/or civil aviation authorities are informed of helicopter activities in night flying conditions. In addition, they have to display a well specified transponder code, which makes them visible and easily identifiable on secondary radar.

During the nights of November 29 and December 11, no such helicopter flights had taken place in the vicinity of the area where the sightings were reported.

I would like to clarify one more issue. Helicopters can remain out of the radar line of sight when applying terrain masking tactics such as flying very low in the valleys. However, in 1989 this tactics could only be applied in daytime; doing this in the dark would have been extremely dangerous. Today, better technology is available for military helicopters, but it would still be very difficult or even impossible to make a complete flight without being observed. Once in the line of sight of radar, helicopters are detected because the rotating propellers reflect the radar waves; stealth helicopters do not exist (yet). Knowing this, please note that the region around Ernage is very flat. Any helicopter in the vicinity would have been detected by the surveillance radars and also by the radar of the airfield of Beauvechain which is only 20 km north of Ernage.

5. I am not aware of any letter addressed to me on December 8, 2002; most probably I was abroad.

6. Your paragraph (2) is biased.

You wrote: "Mr. DE BROUWER claims that no aircraft were in the air, not in the night of December 11th and not in the evening of November 29th".

Did I ever claim that no aircraft were in the air?? Can you tell me where you have seen this statement??

There are permanently aircraft in the air over Belgium! The airport of Brussels was active and the airspace over Belgium was used for regular commercial air traffic. Are you claiming that we should have provided a full radar picture of all air traffic over Belgium?

My statement: "None of the four Belgian radar stations had registered any traffic that could have caused this phenomenon".

This statement seems to be meaningless to you. To me, and I hope to the other participants in this debate, this is very clear language.

It is not difficult to plot coordinates on a radar screen and verify whether or not there was low level air traffic in this region around the specified time. Don’t forget that during night flying all aircraft (including helicopters) have to display their transponder code which makes it easy to track the individual flights and verify what their flight profile is. All other traffic can be considered as "suspect" and are subject to further investigation. However, no additional other echoes showed up on the primary radar, except a few radar parasites (angels). My staff assured me that there was no correlation with the ground observations. By the way, this was confirmed in the first answer of the Minister of Defence (Ref your email). The recordings were analysed by professional radar controllers who were highly motivated to find an explanation for these mysterious sightings. I fully trusted the assessment of these controllers and I see no reason why this should be questioned.

Before going to the SOBEPS press conference on December 18, I was convinced that we were dealing with laser projections or holograms, mainly because nothing relevant had been seen on the radars. It was only after I had seen the report of Lt. Col. AMOND and listened to the witnesses at the press conference (one policeman, and one Air Force weather forecaster who was stationed at Bierset, a Mirage V unit!) that I realized that these people had seen unexplainable phenomena. The day after the press conference, I asked to double check the recordings of November 29 and December 11, but the conclusions remained unchanged.

Regarding the observations of Mirage jets in the vicinity of the airfield of Bierset; your friend must have a good memory to recall all these details.

But what is the relevance??

The cruising speed of a Mirage V is higher than 750 km/h; the pattern speed is approximately 450 km/h and the final approach speed is 320 to 280 km/h. The latter is also the minimum speed.

I am sure that you must have read the coverage of the November 29 and December 11 sightings in the first book of SOBEPS [Vague d’OVNI sur la Belgique - WVT]. Did you find witness reports mentioning such speeds?? I didn’t read all the reports, but the vast majority (at least 50) of the Nov 29 and the Dec 11 sightings mention crafts that are immobile or move at very slow speeds, MUCH slower than the minimum speed of a Mirage V. Relating these sightings to Mirage V aircraft? Let’s be serious!

Regarding the lights that were seen by your friend on the Mirage V, he must have seen the aircraft in its final approach, or just after take off before gear retraction. The Mirage V has two lights side by side on the nose gear and they only function when this nose gear is down and locked. On landing, the pilot sees the effect of the lights on the runway in front of him once the aircraft is at 15 to 20 m above the ground. In normal flying conditions, these lights don’t function because tactical fighter aircraft don’t wander around with their gear down and landing lights on; they only do this for take off and landing. Flying around with the gear down is normally not allowed and makes the aircraft very difficult to manoeuvre; it has to fly much slower than its normal cruising speed, needs high power, consumes buckets of fuel and makes a hell of a noise.

The lights on the wing tips are the usual navigation lights which can be seen on any aircraft. Do these navigation lights correspond with the three individual bright lights which have been seen by multiple witnesses? Let’s be serious!

Referring to your question regarding publication on your website, please publish any information that you want, but make sure that it is correct. I had a look at your site and some of the information is NOT correct. This is not of my business; except if it becomes personal. Furthermore, I suspect that Colonel AMOND may have some remarks as well. I remember that he told me that he had spoken to Mr. PAQUAY and had given him all the details of his observation, including the fact that the craft came as close as 100 m, before Mr. PAQUAY made his calculation.

Major General (Ret.)
Lubbeek, Belgium

Our reply :

Our sincere thanks to Gen. DE BROUWER for his valuable and much appreciated input.

Below is, slightly edited, the point-by-point reply which CAELESTIA’s project coordinator posted on the forum of the European UFO Network on July 12, 2008.

1. True, but only if you accept Mr. AMOND’s statement that the object approached the car to within a distance of "100 to 200 m". The paragraph from which Gen. DE BROUWER extracted my statement referred to the early stages of our inquiries. At that time, Mr. PAQUAY and myself had to rely on a map that indicated that the distance between the parked car and the unidentified object was approximately 1,000 m. Considering a distance of 1,000 m instead of 100-200 m, the 270° turn would have been considerably less tight and the true speed of the object considerably higher than 20-30 km/h. Add to this that witnesses tend to underestimate distances at night, and it’s perfectly reasonable to conclude that the flight path described by the witnesses fits well within the manoeuvring capabilities of a helicopter. As pointed out in earlier correspondence, it was only recently that we learned from Mr. AMOND that the map we used was "NOT accurate" and that the distance between the car and the object was in the order of 100 rather than 1,000 m. But more about this at the end of this reply.

2. Well not in my case, and this despite the rural character of the site were my encounter took place. I never understood why I didn’t hear any noise (that is until the helicopter had already moved away to a considerable distance). One explanation I proposed was that the sudden confrontation caused some form of psychological shock, a state of paralysis or disassociation that blocked the normal workings of my senses. I explained as much in an earlier post and added that something similar had happened to me when a speeding car hit me two years ago, but these explanations were posted on the EuroUFO list before Gen. DE BROUWER entered the debate. With my own experiences in mind, I wondered if, perhaps, something similar had happened to Col. AMOND and his wife. However, when Martin SHOUGH called my attention to the fact that Mr. AMOND and his wife seemed very aware of what was happening (they stopped the vehicle, turned off the engine, opened the window and listened with "ears pricked), I abandoned that idea.

3. I never implied that the average BAF employee is incompetent, stupid and brainless. I was just trying to find out on which grounds exactly the BAF had concluded that aircraft could not account for the sightings. There were two options: (1) there simply was no low-level air traffic in the area at the time of the sightings, or (2) there WAS low-level air traffic in the area at the time of the sightings, but it was assumed that the shape and flight characteristics of normal aircraft could not explain the shape and flight characteristics attributed to the unidentified objects.

I hope Gen. DE BROUWER does not rank me among those who think that you should never believe a word the military say. In the aftermath of the Belgian wave, I received quite a few letters, emails and telephone calls from people (including reporters) telling me that "the Army" was clearly hiding something and that Mr. DE BROUWER either was used as a pawn or was knowingly a part of the scheme. When replying to these allegations, I always pointed out that this was not my view, and that Gen. DE BROUWER had always struck me as an honest and highly competent man (the general and I met on two occasions).

4. I am most grateful to Gen. DE BROUWER for sending us these long anticipated specifications. They are a serious blow to the helicopter explanation and to Renaud LECLET’s work in particular (for Gen. DE BROUWER’s information: Renaud LECLET was the first investigator who studied the possibility that helicopters were responsible for some of the key sightings of the Belgian wave).

5. This is painful. Had we obtained all of the above information back in 2002, it would have saved us a tremendous amount of work. (Jus for the record, I still have a copy of the 2002 letter in which I asked Gen. DE BROUWER if he would be willing to assist in verifying the helicopter explanation for the Ernage sighting.)

6. Gen. DE BROUWER says he never claimed that "no aircraft were in the air" and asks me if I can tell him where I saw that statement.

Apologies are in order here as I misphrased this completely. My remark should have read: Gen. DE BROUWER’s reply seems to imply that there were no aircraft anywhere near Ernage in the evening of December 11, 1989, nor anywhere near Eupen on November 29, 1989.

Next, Gen. DE BROUWER emphasizes that "There are permanently aircraft in the air over Belgium!" and asked if I was claiming that the Air Force "should have provided a full radar picture of all air traffic over Belgium".

I regret we were not more specific in wording our Parliamentary question. For example we could have asked for the position, flight direction and altitude of every civil and military aircraft within a well-defined radius around the sighting location and within a well-defined time frame. In the months that followed the first series of sightings, normal aircraft (especially helicopters and airliners) caused numerous reports of triangular objects equipped with bright white lights and a red flashing light. It is not uncommon for people to mistake normal air traffic for UFOs. So yes, it was important to have specifications regarding all the aircraft that were in the area at the time of the sightings.

As for the statement: "None of the four Belgian radar stations had registered any traffic that could have caused this phenomenon", Gen. DE BROUWER says it may be meaningless to me, but will be "very clear language" to the other participants in this debate.

I personally think most participants will agree that this statement DOES leave room for interpretation. Going by this one sentence, there was still a possibility that one or more helicopters were in the area that night, but that their presence was considered irrelevant because a helicopter didn’t match the descriptions given by the witnesses.

With regard to Gen. DE BROUWER telling us that "The recordings were analysed by professional radar controllers who were highly motivated to find an explanation for these mysterious sightings" and that he "fully trusted the assessment of these controllers and sees no reason why this should be questioned". I wish to repeat that I wasn’t questioning anyone’s skills. I just wondered how the BAF reached its conclusion that no air traffic could have caused the phenomenon.

As for the "good memory" of the person who observed the Mirage jets in the vicinity of the airfield of Bierset, I informed the general that the witness to these events was none other than Roger PAQUAY himself. Mr. PAQUAY had written down what he had seen only a couple of days after the incident. He is absolutely certain about the date and remembers the evening very well.

To Gen. DE BROUWER’s question what the relevance of all this is, I replied that this seemed rather obvious to me. After all, these military jets were operating only 40 km west of the sighting location at exactly the same time the unknown objects were spotted. Certainly, this raises some pertinent questions, such as: - Did any of the pilots report seeing anything unusual in the sky during these manoeuvres? - Did they observe the luminous display over the lake of Gileppe which lasted about one hour and allegedly involved two lights which repeatedly moved away from a central light over a distance of several thousands of metres? - Where the pilots interviewed at all? - What was the nature of these manoeuvres? - How close did their flights take them to Eupen? Probably not VERY close since none of the Eupen witnesses reported seeing or hearing jet planes that night. Still, I think there are plenty of reasons why the presence of these Mirages can be relevant to solving our mystery.

Gen. DE BROUWER points out that "The lights on the wing tips are the usual navigation lights which can be seen on any aircraft" and asks "Do these navigation lights correspond with the three individual bright lights which have been seen by multiple witnesses?"

I never wrote, nor insinuated, that the Mirages were responsible for the sightings reported from Eupen and surroundings! Mirage jets are, of course, too fast and too noisy (same reason why we ended up rejecting the F-117A explanation). One exception perhaps: the small lights moving left and right of the white ball that was seen over the lake of Gileppe. Could those have been distant jets flying in circles in a horizontal plane? Just a thought.

Gen. DE BROUWER writes that some of the information on our site is "NOT correct". We would appreciate it a lot if the general could tell us where exactly we went wrong, so that we can set matters straight as soon as possible.

One final remark with regard to Col. AMOND’s claim that the unidentified object approached his car to within a distance of 100 to 200 m. Gen. DE BROUWER asserts: "I remember that he [Mr. AMOND] told me that he had spoken to Mr PAQUAY and had given him all the details of his observation, including the fact that the craft came as close as 100 m, before Mr PAQUAY made his calculation".

This is incorrect. CAELESTIA received Mr. PAQUAY’s calculations of the spotlight’s diameter on October 27, 2007. Col. AMOND mailed Mr. PAQUAY his own map with the object’s "correct" flight path only on February 28, 2008. There were several contacts between Mr. PAQUAY and Mr. AMOND, but as far as I know, none of these took place prior to February 2008.

Already in previous correspondence I pointed out that, in 2007 Mr. PAQUAY worked with the only map available at the time. This map is very detailed and was made with the help of a printed map (even azimuth indications are given for the different phases). Prof. MEESSEN explained to us that this map was actually based on another map, one that was part of an investigative report compiled by "a mathematically minded" SOBEPS investigator who interviewed Col. AMOND and his wife shortly after the event. It was only in recent correspondence that Mr. AMOND pointed out that the map we used was "NOT accurate" and that the details in the SOBEPS report that deal with distance, altitude, trajectory and size do not match the information which he provided to the SOBEPS investigator. In short, if this map published in Vague d’OVNIs sur la Belgique and in Inforespace is inaccurate, one should blame SOBEPS for publishing a sloppy document, not Mr. PAQUAY or myself for having considered it a useful tool.



 Received : 07/14/08  Helicopters noise - 4 / Banking angles - 1   Joe McGONAGLE   

I don't claim to have the detailed aeronautical experience of General DE BROUWER, but during my own military service, I did have some exposure to helicopters as a passenger and as an observer from the ground.

I have had the privilege to fly (as a passenger) in several different models including the Lynx, Scout, Wessex, Puma, Sea King and Chinook during my army service. Of course, I had the opportunity to observe far more than I actually flew in. I have often come across circumstances where I could see a helicopter clearly, but was unable to hear it (possibly due to the prevailing wind direction) yet in many other cases, I heard them some time before I was able to locate them in the sky (or before they appeared from behind trees/hills/etc.). On a few occasions, the sound seemed to come from a different direction than the helicopter was actually in - I'm not sure if this was a ducting effect, or if I was hearing an echo, but not the original source.

As for the banking angle, I think it always looks steeper than it really is. On one flight in a Lynx, I am sure the pilot was deliberately trying to frighten a female passenger (it was a night flight under exercise conditions) and he threw the a/c around more than I have experienced before, though I don't think we actually banked more than 20 degrees at any point.

However, I never flew upside-down in a Lynx as in this image.

Although perhaps just of academic interest, I found the following in relation to helicopter bank angles :

"Airspeed during the turn does not affect load factor, because for a given bank angle the rate of turn decreases with increased airspeed, resulting in no change of centrifugal force. Note that for a 60 degrees bank turn, the load factor for any helicopter is 2 G regardless of its airspeed (Figure 6-2 refers). This means that a 3000 lb helicopter in a 60 degrees bank turn will, in effect, exert 6000 lbs of force on the helicopter structure. Bank angles of up to 30 degrees will produce only moderate increases in load factor that are acceptable under most flight conditions that you will encounter. The load factor rises at an increasing rate at bank angles over 30 degrees, and may produce unacceptable disk load depending upon the helicopter gross weight and the prevailing flight conditions.

The standard rate turn is a turn at the rate of 3 degrees per second. The rate at which a helicopter turns is determined by airspeed and angle of bank. At a given airspeed a specific angle of bank will provide a certain rate of turn. A simple way to estimate the angle of bank required for a standard rate turn at a given airspeed is to take 10% of the airspeed (mph) and add 5 to the quotient or add 7 to the quotient if the airspeed is in nautical miles (kt). For example, at 100 mph, (10 + 5) = 15 degrees of bank; at 80 kt, (8+7)= 15 degrees of bank."

Stoke-on-Trent, UK

[Though his interest in UFOs was sparked in the 1970s, Joe McGONAGLE didn't become an active researcher until 1999, when he set up an Internet email list for people interested in UK ufology. In February 2007 the list had in the order of 100 registered members, including some well-known authors, investigators, and researchers (the list can be joined at ufologyinuk, registration is free). One of Joe’s main areas of focus is the history of British ufology and in particular the role of the MoD in it.]


 Received : 07/14/08  Helicopters noise - 5 / Banking angles - 2   Martin SHOUGH   

Thanks for your input Joe. Yes, clearly it can happen that when the conditions for sound propagation and other witness circumstances are unfavourable people can fail to hear helicopters. Your and Wim's experiences attest to this.

The issue in this case seems to be as Wim said that the propagation conditions we can measure or infer, and the circumstances of the witnesses, all appear to have been favourable for hearing sound.

I can add anecdotal evidence from a friend whom I credit who has worked in aviation all his life - from managing cargo and passenger airlines to commentating airshows all over the world. I asked if he had ever failed to hear an approaching helicopter in similar circumstances. He responded "I have never been in the situation you describe. All helicopters in my experience would make a hell of a racket".

Your experience with the Lynx helicopter would tend to support Gen. DE BROUWER's statement that a slow manoeuvring helicopter "will not take any significant bank; otherwise it would fall out of the sky".

But estimation of bank angle by witnesses on the ground might well be exaggerated, as you also suggest. Witnesses seem to generally overestimate all types of angle. And Wim's point is also valid : a helicopter several times as far away as Col. AMOND's new testimony indicates could be flying several times as fast as his new testimony indicates, and could accommodate more bank. This could fit his original testimony.

But we come back again to the several other interlocking arguments that make a silent helicopter difficult to defend in this instance, to Gen. DE BROUWER's explicit report that BAF radar experts ruled out the presence of a helicopter, and to the context of other analogous reports in the same time frame describing a similar unexpected absence or near-absence sound.

At least, that last point is my impression from reading some of the summarised accounts of the wave. It would be interesting to see that quantified and applied to the hypothesis that special or 'freak' conditions applied in a number of quasi-independent sightings of helicopters in different environments at different times and dates.

Strathconon, Scotland

Our reply :

As pointed out in our reply to Prof. MEESSEN’s response of July 26, CAELESTIA has agreed to put the helicopter theory to rest, at least temporarily. The various assessments that have been made, and in particular the fact that no sound was heard, the fact that no flight plan was introduced and the fact that no helicopter was detected on any of our country’s radar screens, seem to rule out an "ordinary" army helicopter like a Puma or a Seaking.

So, is it possible that the unidentified object seen at Ernage was an advanced stealth helicopter from a foreign military testing our Belgian radar system? We have no way of knowing, but considering that the first test-flight with a helicopter of that type (the US Army Comanche RAH-66) occurred on January 4, 1996 (, i.e. more than six years after Col. AMOND’s sighting, we don’t think this is a very likely alternative.

With the helicopter now in the fridge it is perhaps time we got the blimp out again (we put it on ice in 2000 when our efforts to consolidate this possibility proved a dead end - see page 2 of our article Triangles over Belgium). Of particular interest in this regard is the news item below which contains images of an illuminated blimp flying over houses and trees in the Boston, Massachusetts, area in the Summer of 2007.

The advertising blimp that can be seen in this clip and which, according to the reporters on duty seemed to have been flying around without a flight plan, prompted concerned residents to call local 911 operators. Upon viewing these images one will note three lights forming an isosceles triangle, a red blinking light underneath the gondola plus the trapezium-shaped front windows flanked with smaller windows. Try to imagine what this would look like with three white lights (instead of one white, one red and one green) and with the lights inside the transparent envelope turned off and the light inside the gondola turned on!

Also, blimps are capable of performing complete turns. They can raise or lower their nose and fly very close to the ground, thus avoiding radar detection. The sound these motorized balloons produce is much more soft than that of a helicopter and is more easily masked by passing traffic (Col. AMOND stated that he not only saw a train pass by at the moment of the sighting, but also heard the regular noise of traffic on the N4 highway). The sound produced by a blimp is also comparable to the sound reported by other UFO witnesses that night (and which has been described as a very faint "dull, humming sound"). And last but not least, some of these witnesses also claimed to have spotted a big, round mass on top of the three white lights.

So it seems that we may have found ourselves a "new" candidate explanation for the sightings of December 11, 1989.


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