BOAC

Just so I do not cause unnecessary obfuscation on this thread - I am NOT suggesting that somatogravic illusion contributed to the accident - I just do not know - I am merely trying to help HN39 understand the phenomenon in view of the comments he/she has placed.

HazelNuts39

BOAC,
Right, like I said, applying brakes changes the perceived acceleration (GIA).

EMIT,
Thanks. I know all that.

EDIT::
Imagine a person swinging on a swing, eyes closed, moving rigidly with the swing, ignoring the wind and air resistance, what does he feel? He feels the rotational movement of his body (the somatogyral effect), he feels the GIA changing in magnitude, but the direction of the GIA relative to his body does not change, until you start braking the free movement of the swing. He could be standing upright without falling off.

EDIT2::
I am primarily responding to rudderrudderrat's post which dealt with the situation prior to stall. I'm not ruling out somatogravic illusions after the stall due to the dramatic increase of drag resulting from the stall.

BOAC

- if you said "A somatogravic illusion can also be a false sensation of acceleration that results from perceiving as vertical the direction of non-vertical gravito-inertial acceleration or force" we'd be there!

PS A simulator has no wheelbrakes.so "applying brakes changes the perceived acceleration" just cannot happen. How else do you think you can "change the perceived acceleration"?

HazelNuts39

BOAC,

Are you being serious? Applying brakes on a moving airplane after landing changes the perceived acceleration. Since the simulator is stationary and has no wheel brakes, it changes the perceived acceleration by tilting the cab. Is that better?

BOAC

Yes, much better. So you accept that a pitch attitude can produce a sense of acceleration - I began to think from your previous that you didn't.

In relation to "are you serious?" it was your post that made ME wonder and I think it was also Why disagree? You have just agreed!

HazelNuts39

I've never disputed that, nor have I disputed that somatogravic illusions can occur. What I'm arguing is that the combinations of pitch attitude and longitudinal accelerations that occur in maneuvers at more or less constant total energy (or at quasi-constant rate-of-change of total energy) - e.g. the swing analogy - do not result in somatogravic illusions.

roulishollandais

PNF inaction : I found very strange that crew :

1 former Steward as CPT
1 former Air Traffic Controler as PNF
1 cadet as PF...

As the Controllers are not allowed to "suggest" actions to pilots, and that was his position for some years, when he got a pilot would he have been shy to "suggest" some actions to the PF ? (just an idea)

BOAC

.....not a lot 'odder' than any other explanation we have so far, Rouli. I do, however, feel that the preservation instinct would kick there and over-ride such 'structuring'.

Personally I don't think PNF had a clue what the a/c was doing. I also wonder about the interpretation of the CVR where he says " you are climbing, go down" - did he meant that but had not seen the altimeter going up to oblivion or did he actually mean "your nose is pointing up, put it down"? Until very late there seemed to be no recognition that despite the nose being in 'Climb' mode, the a/c was actually in 'Descent' mode. It appears, unbelievably, that these two, and make that three eventually, believed that a high nose attitude was all you needed to go up.

Clandestino

No, but you keep on talking about unloading, maneuvering with respect to Gs and all the other neat stuff that works very well on high power, high drag machines with low aspect ratio swept wings that are used to bomb the out of the opponent or shoot down his aeroplanes. While some of it are applicable on high power loading, cruise efficient and not very maneuverable machines we use to transport passengers from, A to B, training airline pilots in them would be utterly superfluous as there are already proven and taught procedures to deal with just the stuff that was thrown onto AF447 crew. They did nothing resembling them.

Aeroplane was stalled by then. There are significant differences in flying qualities between stalled and unstalled aeroplane.

FBW Airbi are flightpath stable in any altn law so the effect of the changing thrust on pitch is automatically canceled and at the computed airspeed at the time stall warning went off the second time, flight controls authority would be pretty sufficient, especially as the difference between TOGA and cruise power at altitude is minimal. Powervise, there is a world of difference between same N1 at cruising level and at sea level - and concomitant pitch moment.

Graph shows right stick to be most of the time in the nose up area, confirming BEAs finding that aeroplane behaved as commanded.

So "run out of speed" shouldn't be misread as: "...and then stalled" but as "...and then got so slow to activate stall warning that made CM2 pull and consequently stall the aeroplane." I apologize for misunderstanding your post.

Your interpretation. Incongruent with busting the level by couple of thousand feet subsequently.

I have already posted that successful succumbing to somatogravic illusion requires higher levels of acceleration - such as a TOGA kick. That's what made Air Transat crew succumb to it, not average acceleration. Popping the speedbrakes on the very fast jet might lead to similar Nx values in deceleration sense but I think we have already established that such an equipment was not used on the AF447 route. Now it is possible that mere deceleration of climb can make the pilot succumb to somatogravic illusion and perpetuate the climb into the stall but anyone proving it will open a whole new chapter of aeromedicine.

Suddenly realizing that instruments are not infallible and losing all faith in all of them? Any rational thought abandoning them for good? What difference does it make if they succumbed to this or that illusion anyway?

...yet the average was nose up.

IBEAHO:

There is a picture that goes with it. Also one on the page 97 of the French report (fig 64) - very ugly stuff.


Probably we wouldn't be discussing AF447 at all if it were the only thing they didn't appreciate.

...in military. Civvies have it mostly as pitching down in go-arounds as the low drag, cruise optimized designs just can't produce enough deceleration for it to be really dangerous.

RetiredF4

Sorry that i wrongly assumed, that changing g loading, thus reducing or increasing AOA and thus changing flightpath is understood by civvies and also by yourself. Finally it i nothing less and nothing more than a result orientated change pf pitch and has nothing at all to do with the military, although the used terminology is more present there.

For you and the others who didn´t understand:
unload = reduce g= normal acceleration from present value to a lower desired value, usually performed by a nose down flight control input, using the available pitch steering device (Stick, sidestick yoke, trim....).

You agree, that it can be done also by all aircraft with wings on it and would have been the necessary means to keep AF447 within the flight envelope and prevent the stall, when properly performed?

Clandestino

Unloading would save the AF447 but it is far from being only possible solution. Other ones: not pulling in the first place, not disregarding the stall warning, returning to assigned altitude instead of merely reducing the RoC from humongous to merely excessive, etc...

Unloading is the most effective on highly aerobatic, very powerful and draggy designs, such as Su-26 or Su-27.

Old Carthusian

Hello again everybody
Can anyone tell my why after the official report there are 35 pages of debate about what is a fairly clear sequence of events and set of causes? I have no inclination to read these thirty five pages but really gentlemen and ladies the cause is known. We can speculate about the motivations behind the cause but these lie in the area of psychology not technology.

HazelNuts39

... not counting 74 pages in thread no. 9 ...

CONF iture

I have, but as you was, in a way, questioning his opinion, my reply was to support or justify his opinion.

RetiredF4

Not pulling in the first place would have prevented the the whole event, as would have functioning pitot tubes. It is self explanatory.

Returning to the assigned altitude, there starts the problem, if you refer it to the part after initial pullup. This returniung to the altitude was imho exactly what the PF tried, smooth and easy and no coffee cups on the floor and no passenger complaint. But he f**d up badly in the pullup and a normal return to the assigned altitude like in day to day flying with easy initiation and all doing nicely worked not out as planned. The speed decayed unobserved due to failed pitots and unnoticed due to lack of common sense concerning aerodynamics and energy management near the service ceiling of the aircraft. The necessary recovery action was time critical.
In this situation returning to the assigned altitude has to observe those specifics and the primary focus has to be angle of attack reduction and speed conservation. The normal parameters for changing altitude or regaining altitude like a special pitch change, a special change of vertical speed, a known SS input might not work in the time available.

I referenced the amount of change to the normal load factor value, as that one is documented in the FDR. I´m well aware that afaik neither AOA nor normal loadfactor are readily displayed in the cockpit.

Unloading can be performed in any aircraft and is done during any approach to stall recovery. On which aircraft it is most effective is of no relevance to the discussion here.

My post has nothing to do with a special maneuver, what i´m saying is that an early recovery atempt before SW2 was made, documented by the normal load factor in the FDR, computed by HN to be +.87 in the average, but that it was not agressive enough.

HazelNuts39

It would have been sufficient, had it not been terminated too early. Why the PF reverted to pulling the nose up remains the biggest mystery of all for me. The report mentions the return of the flight director, the fixation on overspeed, training exercises at low altitude ...

P.S. What strikes me in the various 'level bust' incidents, and in the pitchdown of QF72, that pilots react instantly to an overspeed situation, but are remarkably relaxed when the airplane climbs 3000 ft towards its stall ceiling.

rudderrudderrat

I know you have. What's your source of information, or is it something you just make up?

Please see slide 24 of Operator s Guide to Human Factors in Aviation or somatogravic%20illusion.ppt

According to my maths, accelerating from 170 to 200 kts over 10 seconds is about 3 kts/sec.
The graph of AF 447's ground speed shows a deceleration rate of about 3 kts/second during the climb from FL350 to FL 380

If an acceleration can produce a sensation of 9 degs nose up, why can't a similar deceleration produce a sensation of 9 degs nose down?

See Operators Guide to Human Factors in Aviation.

The difference is it may explain why two qualified pilots made those errors that night.

HazelNuts39

Taking its definition literally, a pilot is under somatogravic illusion anytime he is flying on instruments but believing his bodily sensors rather than his instruments. Since that is contrary to basic instrument flying training, there must be some extraordinary combination of circumstances for this to happen. Is a deceleration of 3 kts/sec sufficient explanation by itself, for two qualified pilots at the same time?

It can, but when it is caused by the attitude being actually 9 degrees nose up, the sensation would be that of level attitude.

Clandestino

I have repeatedly warned against trying to build advanced theories while having no firm grasp on the basics. It was a win-win proposal for me.

Folks listen to me, bandwidth wastage gets reduced.

Folks disregard, I'm kept entertained.

For those unable to take subtle hints: anyone proving somatogravic illusion played a role in AF447, or for that matter that the illusion of pitch down due to deceleration in any airliner incident/accident, would make such a breakthrough that he would stand a good chance of winning both Collier trophy and Nobel for medicine. Good luck with it and don't try to do it with G-CPAT incident, it was pitch-up illusion. Basic aerodynamics folks. Lift to drag. Trust to weight.

Oh and thank you for providing very interesting link, rudderudderrat - the one with very vague and general description of somatogravic illusion during takeoff and landing. Applying lessons "learned" from it to instance of UAS in cruise would have been heavy work, leaning heavily on imagination. Anyway:

...cracked me up. Maybe if one is flying Dauntless and opens split flaps in one go. Airliner flaps are a) not so draggy b) never lowered full in one step. Makes me wonder at what operator
was that presentation aimed.

It has to do something with human factors. I mean regarding to posters, not the crew.

First, that's not the way it works in the real life because a) pilots are trained to put safety before comfort b) other similar incidents have shown a) is observed in real life for most of the time by most of the crews. Second, CM2 warned FAs about possible turbulence ahead four minutes before UAS, therefore chances of coffee being a factor were nil. Third, calling sidestick movements recorded on FDR smooth and easy is not something I'd do but then it could be my level 2 English.

True, but it was not even initiated.

In F-4 Phantom. Is it so hard to accept that airline pilots are not trained in ACM so their procedures, while still working as supposed, are not leaning heavily on maneuvering part? Even if they went to Climb thrust/5° pitch at the apex of their climb, aeroplane would stabilize at alpha slightly above 5° and perform gentle driftdown to 5° alpha ceiling.

It is not as important to know the reason and principles involved in procedures as it is important to perform the procedure timely and precisely when required. Now, I'm not saying that detailed knowledge of aeroplane, HF and air is useless, just that many a pilot had successful and long flying carrier while being oblivious to some basic flying facts.

Here we go again:

Pushing the stick full forward on Airbus gives you -1G clean (and fast enough, about which there was no doubt when second stall warning went off). That's enough enough. Now watch the ignorant bite on this one.

Because they are absolutely inessential in transporter! We might install them one day when we go seriously about the business of air combat in A330 but I can't see it happening anytime soon.

No, but is as convenient to derail discussion as is composite fin of AA587, NDB identifier regarding the AA965, core lock of Pinnacle 3701, or who-knows-what-not at Habsheim. Same stuff on anonymous internet fora every time Caucasian (minus Russians) crew stuffs it up. Lesson from worldwide spread of accidents is there are no American/Chinese/Russian/Somali/Graustarkian aerodynamics or physics and flying does not care a little bit about pilots' cultural background, it's just some cultures are more prone to rejecting the traditional and embracing the pragmatic - essential for aviation. Instead of understanding it, what we have on the PPRuNe is a lot folks mistakenly believing that they know something about aviation and gloat about how their cultural circle has better "safety statistics" than some other one. So then comes AF447 and dreams of immanent aeronautical superiority are shattered and we get thread upon thread of nonsense coming from those wounded by their Aeroweltanschauung suddenly shown to be false.

jcjeant

Answer "a la clandestino" (fair enough)
Anyone proving somotogravic illusion not played a role in AF447 would make such a breakthrough that he would stand a good chance of winning both Collier trophy and Nobel for medicine

clandestino
It is certain (for clandestino at least) that AOA is truly one of the less important data
However when this data is outside that prescribed for the airplane ..this airplane become an iron mainly subject to the Newton law ....