AMR 587 Airbus Crash (merged)

[Flap 5]

fiftyfour,

Swept wing airliners certainly are controlable in the stall. It is one of the first things covered on any type conversion. From your description you appear to be refering to the problem of spinning an airliner.

High tail airliners do have a problem in that the high nose attitued causes the airflow over the tailplane to come directly from the disturbed air of the wings, this leads to a deep stall.

However your post has nothing to do with the topic under discussion which refers to the vortex wake turbulence incident of AMR 587 which became an accident after incorrect pilot control inputs of the rudder.

[Notso Fantastic]

54, you are, I believe, holding a few misconceptions. Airliners are designed so the last bit of the wing to stall is the wingtip. There is a discussion on this in TECH LOG-'Windshear Question'. You don't want the wingtip to stall first because it would give a powerful nose up moment at a disastrous time, and if asymmetric would turn you upside down. So you see design tricks on most aeroplanes to prevent the tips stalling before the wing:
1- reduced sweepback towards the tips
2- reduced incidence
The 747 most certainly remains very controllable in a stall- it wallows and behaves very well.

We are starting to chase our tails with this discussion, with a massive amount of irrelevancies being brought in! There was no stall. It was nothing more than a powerful wake encounter- something experienced by most professional pilots. It's a matter of technique.

[Raas767]

I have not been following the investigation of 587. Nor have I read all the threads speculating on one thing or another. I am not an engineer, nor did I fly in the military. I have, however, flown commercial jets for 11 years, turboprops before that and spent a few years instructing before that.
Never in my training or in any aircraft manual that I can recall did it mention any warning concerning rudder reversal. On the contrary, everything I have read says that bellow Va FULL use of flight control is permitted without overstressing the airframe. AFTER 587 we received all kinds of training and warnings about prudent use of rudder. That being said, perhaps the manufacturer never imagined a pilot using the rudder so aggressively. I certainly never would in a wake encounter and I doubt First Officer Molin did either. As a matter of fact the last thing I read about the speed of the rudder deflection would make it physically impossible for him to even move the rudder that fast. Coupled with the history of uncontrolled rudder movement on the A300 on two previous occasions involving AA aircraft alone I would suggest caution before we nail these two gentleman to the proverbial wall. I had the previlage of flying with both of them on separate occasions on the 727 and found them to be very competent aviators.

[Groaner]

Not meaning to hijack the thread, but this is an excerpt from the current issue of "The Economist" - usually a reliable magazine (in an article about counterfeiting):

At least as hazardous is the trade in counterfeit car parts, which may account for as much as 10% of the spare parts sold in the EU, according to a 1999 study. Even more worrying is the thriving trade in reconditioned aircraft components, passed off as genuine parts along with fake certificates of authentication. Last year, police raided three aviation-parts manufacturers in Rome, seizing more than $2m-worth of used parts—modified and repackaged to look as good as new.

Dodgy aircraft parts kill. In 1989, a plane belonging to Partnair, a Norwegian charter airline, crashed when its tail assembly fell off because of substandard counterfeit bolts holding it to the rest of the body. The CIB believes that the November 2001 crash of an American Airlines flight over New York may have been caused by the failure of counterfeit parts.

Has anyone heard anything about fake parts being used?

(Note to journalists: this is entirely hypothetical, and may well be a case of mistaken identity or similar)

The "CIB" they are referring to is the Counterfeiting Intelligence Bureau (CIB), part of the International Chamber of Commerce.

[Anthony Carn]

Raas767

..........everything I have read says that bellow Va FULL use of flight control is permitted without overstressing the airframe.

Va relates to wing stall before overstressing of said wing. It certainly does not include the use of full rudder.

If Va included full rudder useage at wing stall, then you'd be authorising FLICK ROLLS, on any aeroplane, provided you're at or below Va !

If that's your interpretation, then please let me know which airline you fly for and I'll avoid it ! (only joking).

I just could'nt let that one go, sorry if it's off-thread.

(Fundamentally, we need to agree here that full rudder useage is'nt something that's necessarily permitted or necessary, except for single engined operation and (in an extreme case) landing. Fins are "easily" overstressed.)

[Flap 5]

Raas I do not believe the pilots are being condemned on this one. According to the tv program it was the airlines procedures that were being criticised. They should have known better. But, as usual, the threat of litigation means that the lawyer heavyweights come out to protect the airline. The senior pilot in the documentary also made a strange statement where he stated he did not realise that full rudder deflections would cause excessive stress on the airframe. This statement must have been prompted by the concern by the company of litigation.

Unfortunately the litigious society of the US does not encourage the revealing of the truth. It is also going that way in the UK too now, which is a great pity to say the least.

[Raas767]

I just did some thumbing through my old college text books. Not a very thorough search but I did not find anything warning about rudder reversal. When I was in Europe converting my ratings I do not recall being specifically warned about it either. I am not surprised that one of our chief pilots claimed ignorance. If anyone at the training acadamy or at the manufacturer knew then they certainly did not tell us. Other line pilots have said the same thing. Military pilots with engineering backrounds seam to be the exception.
Like I said, For the pilots to have moved the rudder as fast as the FDR suggest it would have been a super human feat. I still maintain that the rudder malfunctioned.

One more thing. Not that any pilot that I know spends anytime dancing on th rudder pedals, I do remember a post here a few months ago regarding something in the A300 manual. I think there was a PROCEDURE there to move the rudder back and forth in order to get the gear down if there was a malfunction. I am not positive about that but maybe someone that flies the jet could check it out.

One more thing. Not that any pilot that I know spends anytime dancing on th rudder pedals, I do remember a post here a few months ago regarding something in the A300 manual. I think there was a PROCEDURE there to move the rudder back and forth in order to get the gear down if there was a malfunction. I am not positive about that but maybe someone that flies the jet could check it out.

[fiftyfour]

Flap5 and Not so Fantastic.
If you know the B747 can be stalled and then 'wallow down' in the stall due to the good aerodynamic features like washout etc etc, that you mention, then I stand corrected.
Thanks.

[Flap 5]

Raas,

The 'book' on any aircraft will say many things that do not translate into real life flying. They are often written by engineers. I have many years and thousands of hours of airline flying and one thing I have learnt is that when the 'book' comes up against common sense, common sense wins.

Indeed there may well be a procedure to get the u/c down by moving the rudder. However the person who devised that one clearly was looking at trying to dislodge the u/c by some means. As the pilot you have to consider how kicking the rudder will effect the rest of the aircraft. You don't just do it because 'the book says'.

[Wino]

And Flaps 5

you don't get to make up a procedure or deviate from one just because you think that ain't right.

I am trying to get a copy to post here of what both Airbus and Beoing sent out to all AA pilots. The differences are EYE opening.

That is MORE dangerous.

Cheers
Wino

[fireflybob]

>you don't get to make up a procedure or deviate from one just because you think that ain't right.<

Wino, I don't think Flaps5 is saying that you should do either of these things.

What he is saying is that there is nothing wrong with applying "airmanship" and good judgement - not that I am implying that the crew of AA did not do so.

[Wino]

Fireflybob,

The Airbus manual called for "rapid alternating sideslips" after extending the gear manually untill a 3 green indication is reached.

He is saying that he shouldn't do that, even though the manual clearly instructs it. So if he had the gear collapse after a manual gear extention because he didn't do the alternating side slips then you can bet your ass airbus would be looking to fry him from deviating from their procedures.

While I also have known about doublets, the manual clearly indicated their was a time and a place for them. If you are saying that the manual is incorrect or that it was lost in the translation, then you have a certification issue on the aircraft right there. If the French cannot produce a manual in plain english (the language of aviation) that is both correct and understandable, then they should not be permitted to certify their aircraft for operations outside of france.

Cheers
Wino

[cwatters]

Sorry to go back a bit but...

Has there actually been any research into how humans cope with nonlinear controls (eg like that found on the rudder)? I tried a web search but didn't find anything that lept out at me. It would seem to be important as we are about to get speed senstitve steering in our cars.

Being English and living in Belgium I am used to driving on both sides of the road. I've been living in Belgium for the last 4 years and feel 100% converted to driving on the right - so why did I swerve to the wrong way recently?

Isn't it possible that a pilot faced with a sudden upset might respond automatically and apply rudder travels normally only used at lower speeds?

[Notso Fantastic]

<I've been living in Belgium for the last 4 years and feel 100% converted to driving on the right - so why did I swerve to the wrong way recently?> You're looking at it wrong. You swerved the right way- if they will persist in Europe, along with the Americans, at driving on the wrong side of the road, then it's their fault. You were on the right side of the road (which is the left side), they were all on the wrong side. They'll come around one day.
Pilots having to make large movements on the controls will always have an idea of their speed and the relative safety of large control inputs. Nobody at high speed is going to slam full deflection on unless absolutely essential. Full deflection of the pedal will not produce full design deflection of the control.
.......we go back around in circles in this topic!

[Few Cloudy]

Long Thread - lost comments - conclusions.

What you say about going in circles is correct Not so Fantastic. I have just taken the trouble to go through this complete thread - God knows what the phone bill will be - but one thing is for sure - most questions and comments coming at this stage have been handled earlier on.

However three thoughts repeatedly occured to me as I did this scan.

The first is that training for jet upsets is creative training to deal with a worst case situation - including tricks to save an aircraft from a hopeless attitude/speed/rate combination. Was this really the situation in which the Airbus found itself? If it wasn't, then the trained upset inputs were inapropriate in this wake turbulence encounter. Whose fault this was we can't say. Training programes have a habit of being taken on board differently and applied differently by different pilots. Let us learn this lesson when writing future programmes.

The next thing is that use of rudder to correct wing drop is only appropriate in a stalled situation. The reason for it is that use of aileron increases the effective angle of attack on the dropping wing, thus in theory stalling it even more. Depending on the design of the aircraft (washout - tip sweep reduction ) and where and to what extent precisely the wing is stalled, this may or may not be the case. Using the rudder simply to right the ship when the wing is NOT stalled, however, has to be bad advice.

The third thought concerns design. Even the DC-9 family had a rudder limiter, consisting of a horn shaped interference pin fitting into a gap on a traveller directly attached to the rudder. The pin was operated by pitot (dynamic) pressure and was there to allow only appropriate rudder inputs for the engine failure case. If you get the chance, reduce thrust on an engine in cruise to idle and you might be surprised what a very small effect this has on yaw at cruise speed. Thus only a small deflection is required - apart from the fact that the rudder effectiveness increases with speed. The designer was being cautious in giving the pilot the rudder authority he NEEDED to deal with engine failure. It may well be that this authority in certain flight modes would suffice to damage the aircraft if mis-applied in an oscillating sense, for which neither the empennage, nor the rudder has been designed. Again - let us teach our pilots what such use may cause, which is the real reason large jet pilots are not taught, as light aircraft pilots may be, to use rudder in all turn manaoevers.

[Notso Fantastic]

Agreed, especially the 3rd. para. I think it fair to say all pilots who have flown T-Tails give extra care and attention to rudder handling. You want to look after your empenage 'cos there ain't a lot you can do without it! I cannot think of a valid reason for rudder reversal. Certainly not rapid, ever! If you push wrong rudder on in an engine failure scenario, then pushing it the other way is the only conceivable time. The change in sideslip will have to be very carefully handled, even doing it slowly.

The lessons have now been learned........haven't they?

[cwatters]

> .......we go back around in circles in this topic!

Not quite my intention. I too have been back through all 16 pages.

I wanted to know if anyone had seen any research on how well (or how badly) people are able to use variable sensitivity controls. Can people adapt or do they react badly when something unexpected happens? I spent some time looking for papers on the web but couldn't find anything.

I suspect that when someone is "surprised" they subconsiously revert to using controls in a way that represents the sum or average of their lifetime experience, rather than how they are behaving at that particular moment.

Jshg wrote..

>I recall a cross-wind approach some years ago when
>the PF reverted to his previous turboprop type and
>applied rudder in the last 500'.

Wino also made the point..

>You will see that Sten used no more than 1/3rd or so
>of the available rudder travel to keep the plane
>rolling down the runway. When the wake encounter
>happened, those same inputs are now FULL TRAVEL inputs.
>There is no way in 40 seconds or so he could adjust to
>the increased sensitivity,

I suggest that even if he had adjusted to the increased sensitivity he may have been powerless to prevent himself "reverting" when suddenly surprised by the wake encounter.

A common design issue with all systems that contain feedback is the need to maintain stability and avoid conditions that cause the system to oscillate. Anything that adds a time delay in the loop usually makes this harder to achieve. This paragraph I found on reaction times might be relevant..

http://www.visualexpert.com/Resources/reactiontime.html

>Psychological Refractory Period
>
>Following a response, people exhibit a "psychological
>refractory period." During this period, new responses
>are made more slowly than if there had been no previous
>behavior. For example, suppose a driver suddenly steers
>lefts and then right. The steer-right response will
>occur more slowly because it immediate followed the
>steer-left.

Which seems to imply that when you are trying to damp out oscillation your reaction times are reduced. "Heavy" forces would also add a time delay.

Whatever the true position, it appears the pilot in 587 felt the plane was oscillating and applied several rudder reversals to try and stop this.

(and yes I have read the posts that say he shouldn't have used rudder anyway).

[Notso Fantastic]

I think we are digging into obscure academic areas and chasing our own tails again. It's been talked to death. Variable sensitivity controls are discussed in several previous posts, not least 3 posts before yours.

It's not unusual for pilots to 'cheat' by tweaking a bit of rudder, usually on approach at low speed. Different types have very different responses at this stage. They had a severe wake encounter, full control reversal inputs were applied either automatically or manually. The fin separated. At low flap retraction speed, it is more acceptable to apply full rudder than at cruise speed. It was the reversal that did the damage. Rather than discuss to death the principles of pilot input, I think we should satisfy ourselves that this is not some system error. If it is pilot error, we should all learn by it.

[hobie]

please excuse me if my technical term "Fast Data Recording" is not strictly correct .....

my question ......

"Fast Data Recording" is employed to routinely monitor Pilot/aircraft performance/procedures on large passenger aircraft and to highlight deviations from standard practice or identify "Bad Practice" etc ......

I "almost" get the impression that the PF on this flight may have been the first pilot to have ever used his rudder in the "Aggressive" way that he did (I appreciate that malfunction has still to be ruled out) ......

surely routine data recording would have highlighted over time that Rudders were being used excessively and that load limits etc were being exceeded? ..... or is this almost a "One Off" ? ....

cheers .... hobie ......

[OVERTALK]

In Daze of Yaw

Not much is being said about AA587 since Airbus imposed its will upon the last hearing. The pilot error theory

is being supported by the NTSB and endorsed by the FAA. The glitch is more likely (IMHO) to be in the original

design (or introduced later by a software patch)._

And I still like my original theory (below):

So, (in part) addressing these selected quotes:
A. "A good look at the DFDR data does not show rudder movement consistent with a mechanical problem." and
B. "Even the AA flight 903 incident occurred in violent weather and an inflight upset that may have been a stall

or may have been something else."

In Daze of Yaw
The AA587 explanation may be as simple as water getting into the pitot-static lines every time an A300-600

aircraft is washed (or is parked in torrential rain) - and introducing a pressure change damping effect that

cannot be accommodated by the CADC’s pneumatic “expectations” (particularly in yaw). Why would that (i.e.

trapped water) make a difference? It’s not as if it might freeze in the lines and cause glaring static errors

(in airspeed, altitude and rate of climb). The errors might be much more subtle than that. In fact, in normal

flight they might be hardly noticeable. But in strongly yawed flight it could be entirely different. Why would

that be?

Explanation

_The input to the CADC’s is (ideally) purely pneumatic pressures being mildly differentiated by height and/or

speed variations. The CADC as a sensor is capable of picking up very minute pressure changes and rates of change

of pressure variation (as well as temperature increments of course). It feeds the resolved heights, rates of

climb and (of particular interest and significance) current airspeeds to a range of systems – including the yaw

damper and rudder limiter. _If _water is inadvertently introduced into the static lines (say) you then have a

damped and laggard hydro-pneumatic response in all the variables that feed pressure changes into the air data

computers (which will in turn misinterpret these “damaged” inputs and thus apply incorrect outputs). Normally

there will be four or more static ports (holes) – with a couple each side (of the airplane) to guard against

blockage (of a singular one). The siting of those holes is designedly where, in normal symmetric flight, the

smallest PEc (pressure error correction) requirement is generated. Some aircraft have the static ports right up

the front on either side of the nose and some aircraft have them way down back, just forward of the empennage.

Being thus located either well forward or well aft of the aircraft’s vertical (i.e. yaw) axis, the effect of

yawing needs to be cancelled out (and that’s why you have the ports uniformly on the port and starboard sides of

the fuselage). Works well, but how will water trapped in the lines affect the sensed pressures?


When the aircraft yaws due to turbulence (or pilot-pedal input) any airflows injected dynamically into the

static lines are self-canceling because the port and starboard static ports are Y-pieced together. Net effect on

the CADC’s sensed pressures? Not a lot, although extreme yaw can cause airspeed indications to fluctuate wildly.

But what if water has collected at a low point in the static lines – perhaps before the port and starboard

pickups are Y-pieced together?? (even if only on one side). In a sharp yaw to port any water in a starboard line

would tend to flow aft (and water on the port side would tend to flow forwards). What will be the effect of that

on the air-pressures sensed by the CADC and, more importantly, its outputs? At this point I should also

acknowledge that some modern systems (but probably not the A300) do incorporate air pressure transducers that

convert what is sensed to a digital signal that then goes to the CADCs. But whether those signals were valid or

not would depend on the location of those transducers. Because the CADC senses both quantum change and trends,

there will be at least a lag and more likely a contrary signal generated by the adverse flow of water affecting

the line pressures. Any correction fed to the rudder actuator by the yaw damper might then be inappropriate in

both magnitude and direction. So where is this error headed? Will any initial wake-induced yaw be damped out or

magnified by the yaw damper in this scenario? Will the erroneous CADC signal cause an initial significant yaw to

overshoot equilibrium and, in fact exacerbate the L/R yaw cycle? (i.e. "set the ball rolling" for some

rudder-supported extreme yaw cycling).


My theory says that YES, if the initial externally-triggered yaw is large enough, it could do that. If an

inappropriate correcting rudder deflection is commanded because of water trapped in the static lines and the

wrong airspeed being sensed - and the yaw correction consequently overshoots significantly, then we are into a

rudder-inspired undamped phugoid around the yaw axis. And beyond that “threshold of significant external yaw”,

because of the great stabilizing influence of the large vertical fin, any out-of-phase rudder control inputs

would be amplified and rapidly approach the point where something has to give (structurally). And that is what

I’m guessing may have happened in AA587. It might explain why much anecdotal evidence of tail-wagging is quite

irregular – possibly because static line water trap drains are cleared out on (just guessing) each C service (or

might be even more regularly)._ Then the aircraft's unalarming (but irritating) tail-wag phenomenon would

disappear overnight without comment. That would explain why particular airframes don't get (and keep) a bad

reputation.


So the theory really says: "You'd need to unluckily combine a waterlogged static system and a wake turbulence event (with

its large amplitude yaw “kick-off”) to end up generating an AA587 event".


In my scenario is there any scope for pilot complication or compounding of the wildly yawing initial scenario

(prior to structural failure)? The easy answer is: “Of course”. No pilot is going to sit there and allow the

airplane to swing wildly from side to side. He will at least attempt to counter the yawing with judicious rudder

pedal inputs (at least I would). But whether he could be successful (or just get out of phase himself and

exacerbate the situation) is the real quandary. Would the other pilot be aware of any such intervention on the

part of the PF (pilot flying)? Not really – and the whole thing would happen so fast that there’d be little

chance for anything further than the gasped expletives heard on the AA587 CVR.

How could you test this theory? The easy answer would be to “water” an A300-605 and go out and see whether

atmospheric disturbances or pilot pedal input could bring about any strange unexpected yawing responses. Another

approach would be to monitor the static-line water-traps across the fleet, measure the amounts of water found

and note whether aircraft washes (or heavy rinses) increased this amount.

Addenda
To specifically address this input by ALPA: (particularly the observation in blue)
<<"As I understand it, the A300 -600 was being hand flown at the time of the upset._ So the autopilot

would not have been engaged._ The A300 is not a fly by wire airplane._ It is conventional hydraulic controls so

the FCS electronics would be very limited._ The yaw damper would be active but the rudder

swings far exceed the authority of the yaw damper (it is mechanically limited)._ So, based on the DFDR, I do not

see any airplane issues based on flight control malfunctions.">>

Apart from the sampling issue with the AA587 DFDR meaning that the number and size of AA587's rudder deflections were not determinable, you

would not need max deflection rudder authority for a yaw-damper-actuated rudder to achieve large yaw amplitudes.

It's the timing of the actuator inputs that would be critical. I used to do a low-level jet aero display that

incorporated extreme yawing cycles on a flyby. Rudder authority was such that the last thing you wanted to do

was to stall the vertical fin - so you needed a keen sense of timing when "walking" the rudders somewhat

gingerly so as to achieve peak yaw in each direction. It is quite possible to achieve extreme yawing angles

(talking about > plus/minus 30 degrees here) by just getting the timing right. In addition to that, do not

disregard my opinion above - that any pilot (PF) would instinctively intervene (and perhaps disastrously) once

an identifiable cyclic yaw was underway.