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AF 447 Thread No. 6

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AF 447 Thread No. 6

Old 29th Oct 2011, 02:33
  #1481 (permalink)  
 
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Devil

thermostat said:
You don't have to like my opinion, you just have to learn from it.
This will be my last post on the subject.
One can always hope!
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Old 29th Oct 2011, 03:03
  #1482 (permalink)  
 
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Thermostat, Having been a more than competent pilot, If you won't agree that there wasn't enough airspeed for the elevators to work, once AF447 was stalled, would you agree that the 3 pilots involved were incompetent?
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Old 29th Oct 2011, 09:13
  #1483 (permalink)  
 
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Simplicity

I've read most of the AF447 threads and I am quite surprised by one thing:

Regardless of complexity of the situation with crew been hit by many confusing alerts, flying in the darkness without visual reference, did they doubt about indicators of altitude and vertical speed? (I don't think so, CVR revealed it).

What else than lack of lift => lack of speed can cause falling that bird so fast from the sky? Did they believe that they are in a dive/overspeed situation?

It seems to me that flying modern a/c (plus training) went too far away from simplicity. There are some senior data applicable to airmanship and if they are forgotten then gross piloting errors are the result.

It seems to me that the very basic principles may be neglected in training and too much attention is given to various particular issues which are rendered unimportant once basic skills are out.
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Old 29th Oct 2011, 11:03
  #1484 (permalink)  
 
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"What else than lack of lift => lack of speed can cause falling that bird so fast from the sky? Did they believe that they are in a dive/overspeed situation? "

well, like by many times written above- basicly nothing other than a stall, with high nose up and this sink rate you can exclude a dive. basicly a PPL owner would answer this question.

one thing ist that it was night, possibly IMC and there was turbulence. they probably had not any visual reference to the natural horizon outside and maybe they did not believed the pitch indication on their instruments.

i think the big question we had at the day of the crash WHAT happened is fully answered, it may be of interest to read the thread no1 what kind of speculation there was made. the question WHY it happened will never be answered because the people who know why they pulled until impact will not tell you.
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Old 29th Oct 2011, 12:40
  #1485 (permalink)  
 
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On another tack, given the criticism leveled about the captain taking a break at that juncture, was it because he was especially tired and could that, exacerbated by the consequent very short sleep, have left him a bit dazed/sleepy headed ? Is the inquiry looking into the previous 12 hour activities ?
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Old 29th Oct 2011, 12:50
  #1486 (permalink)  
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the consequent very short sleep, have left him a bit dazed/sleepy headed
- in fact probably around 15 minutes between leaving the cockpit and being summoned back.
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Old 29th Oct 2011, 13:47
  #1487 (permalink)  
 
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Coagie,
Although Airbus could make some improvements, like having the aircraft default to a safe power and pitch, when the airspeed is unknown, I have to put the blame on Air France for not properly training it's pilots in the case of the AF447 crash.
I agree with you 100%. Since the day of the crash there has been endless speculation on why the A330 failed. From theories on the VS snapping off to uncontrolled dives to engine failure, computer malfunction/interface etc...
But as we know now the pilots were helpless in trying to figure out the situation they helped create. The blame is with Air France and there procedures...
This was the "perfect storm" scenario, the result of a chain of misguided decisions starting with flying through bad weather, the captain leaving the flight deck at a critical stage of the flight and leaving the least experienced pilot in control, the failed Pitot tubes (weather related) and then of course the pull back on the SS. It all wreaks of poor training and procedures...
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Old 29th Oct 2011, 13:54
  #1488 (permalink)  
 
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I guess the selective CVR out-takes should advise caution but there seems an odd lack of energy and activity about the whole thing. Hardly a time for quiet contemplation and one would expect the Cptn to become suspicious (rightly or wrongly) of the PF actions when things didn't go as expected and then forcibly intervene. No evidence of heads down activity as computers are re-configued or re-booted, not even a distracting light-bulb failure, so what were they doing - sitting largely in silence ? Were these men exhausted ?
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Old 29th Oct 2011, 14:27
  #1489 (permalink)  
 
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Stability and Control at high AoA and post stall

Bit off-topic but related to discussion on stability and control of transport aircraft - have recently seen presentations and videos related to recent research between NASA and University of Illinois.

A pretty impressive remote control model:-

The remotely-piloted Airborne Subscale Transport Aircraft Research (AirSTAR) generic transport model
NASA AirSTAR Testbed - YouTube
Nasa - AirSTAR (HD) - YouTube

and safe way of testing approach to stall and recovery

Video highlighting testing of an L1 adaptive controller developed by the University of Illinois and University of Connecticut flying on NASA's airborne subscale transport aircraft research testbed (AirSTAR) testbed during a 3-day flight test campaign at Fort Pickett in Blackstone, Virginia from 2-4 June, 2010.

The video shows how the L1 controller makes the aircraft controllable through a mormally divergent roll oscillation and a post-stall region.

AirSTAR was developed in part to help define and augment the control properties of large transport type aircraft in unusual attitudes or post-stall orientations, upsets that have led to numerous loss-of-control accidents, but which are not tested on real aircraft for the obvious safety reasons.
NASA AirSTAR full stall with subscale large transport - YouTube

NASA AirSTAR testing L1 adaptive control for post-stall control - YouTube


In none of the tests I have seen was there a stable post stall, but maybe due to scale it was just beyond the ability of the auto controls/remote pilot?

Last edited by sensor_validation; 29th Oct 2011 at 23:11.
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Old 29th Oct 2011, 14:45
  #1490 (permalink)  
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I think the stability of a swept wing fully stalled airliner has amazed many. Most of us would have expected a departure, I'm sure.

Last edited by BOAC; 29th Oct 2011 at 15:08.
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Old 29th Oct 2011, 15:39
  #1491 (permalink)  
 
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I should imagine some of you will be surprised to read these excerpts from an RAeS Upset and Loss of Control document.

A full stall is recoverable if resolved early in the stall. A prolonged stall condition can lead to an unrecoverable deep stall or a developed spin.
A simple swept and tapered wing will tend to stall first at the wingtips because the high loading outboard, due to taper and is aggravated by sweep-back. The boundary layer outflow also resulting from sweep reduces the lift capability near the tips and further worsens the situation. This causes a loss of lift outboard (and therefore aft) which produces pitch up. A lot of design sophistication is needed, including the use of camber and twist, leading edge breaker strips, fences etc., to suppress this inherent raw quality and cause an inboard section to stall first, so that the initial pitch tendency is a more desirable nose down. However, when a highly developed swept wing is taken beyond its initial stalling incidence, the tips may still become fully stalled before the inner wing in spite of the initial separation occurring inboard. The wing will then pitch up.
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Old 29th Oct 2011, 15:51
  #1492 (permalink)  
 
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Mr. Optimistic.

"An odd lack of energy..." You have concluded what BEA have assumed all would conclude. These are not ill informed boffins who do not know how to create a foundation in the public for conclusions that support a pov. The MEMO was at the behest of Airbus. Foundation for a PR from the company that exonerated the a/c of any "new" fails.

Feigned inexperience at Press functions is de rigeur here. Selected and parsed data is a calculus, my friend. Are you not curious as to why BEA will not release more information? Lack of funds? Fear of creating the wrong impression? "It's too soon...." Why, exactly, would that be?

Why does the Judge demure at further release of FDR? Surely, more data is in the public interest? It is, and that is why it is not released. The Public Interest is not the driving vector, here. Nor is safety, at least the kind that costs money and shows Principals as criminal in their lack of mitigation of current problems.

Spread your wings, my friend, and partake of public buzz elsewhere. It is a battle, ther one trying to access, the other trying to prevent.

In which condition is the lack of disclosure predominant?

Financial, or Criminal? Erm, Both.
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Old 29th Oct 2011, 15:57
  #1493 (permalink)  
 
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Lord Spandex Masher.

And hence, unrecoverable. I follow. I have been gifted with some Airbus data re: THS. Who's up for a discussion? It seems there are other conditions that defeat autotrim beside Overspeed. Some other conditions that subsequently reinvigorate it are included.
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Old 29th Oct 2011, 16:00
  #1494 (permalink)  
 
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BOAC

Define STALL. Then define FULLY. Thanks.
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Old 29th Oct 2011, 20:27
  #1495 (permalink)  
 
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Departure

BOAC
........ Most of us would have expected a departure, I'm sure.
Sorry to object here.

Imho with the term "departure" we adress the point, where the aircraft leaves the region of controlled flight (i.e. departs the flight regime).

There is no doubt, that the aircraft was outside this controlled flight region, was uncontrolled and therefore had departed. It stalled and departed with a high sinkrate and some minor roll oscilations.

Unaccelarated stall and departure like we had here (1g-stall) is less liable to violent maneuvers / g-loads / rolls/ oscilations and therefore hard to discover from the aircraft behaviour alone (without reference to the instruments or to the outside). First sign might be a gentle nose drop in a conventional aircraft, but not in AF447 case, as the FCPC´s where acting to maintain the demanded load factor. This stall has besides the AOA problem (AOA too high) also a speed problem (speed too low for 1g flight). To recover it is necessary to reduce the AOA and increase speed up to flying speed again.

Accelerated stalls (normal asociated with turning) are more sudden and more violent. The flow separation over the wings is not equally distributed and therefore yaw, roll and pitch changes in any random combination are induced. There is a primary AOA problem (g-induced too high AOA) but lesser or no speed problem (speed too low for acelerated flight, but not for 1g flight) and relaxing of g-load does the trick to solve the problem.

The entry into the stall of AF 447 was very smooth, as the speed decay below the stall speed occured in the timeframe, where the PF tried to correct his pitchup by some ND input (g load around 1 g). But the mass of the airframe in combination with the pitch upward vector smoothed the airframe close to the stall (second stall warning). It was initially no AOA problem, but a speed problem (running out of speed in the climb with not enough power applied). At that point speeds where already unreliable. The aplication of TOGA at that critical phase delayed the departure and held the AC in the pitch and in a little bit of climb (for further 500 feet) while further shedding vital speed. But finally the AC just departed by picking up a high descent rate and some roll oscilations.

The slowing during the climb might also have caused some SI (if you slow, you feel tilt forward) and induced doubts about the validity of the pitch information, as airspeed was unreliable already. That would also explain the missing ND inputs (as he felt already ND pitch) and the thinking of the PF at some point later, that they where fast and thus descending fast (not believing the pitch information), not falling / stalling downward fast.

All three pilots saw their problems obviously in the roll oscilations not in speed and AOA. Otherwise primary concern should have been the reduction of AOA and rolling wings level later on, when AOA reached an non stalled value.

Later on when it came to their mind that they are not in some high speed descent, that commanding climb with the SS did not work, they couldn´t get their mindset squared to "being stalled" and the apropriate recovery procedure.

Last edited by RetiredF4; 29th Oct 2011 at 21:11.
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Old 29th Oct 2011, 21:03
  #1496 (permalink)  
 
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Alternate Law 2 - Reduced Yaw Stability

After reading and re-reading a number of A330 documents and checking the FDR traces (p.112), I have tentatively deduced that the aircraft's tendency to a RH roll was directly related to the rudder Yaw Damper inputs.

It seems to me that the Yaw Damper applied left rudder as a LH roll was being recovered and contributed to the next RH roll.

The PF started applying RH rudder at 02:13:03 and over the next 45 seconds kept a RH bias on the rudder which helped to reduce the roll amplitude and the RH roll bias. In the last 40 seconds he left the pedals alone and the RH roll bias returned. It also appears that PF pedal inputs (up to the maximum allowed by the RTLU) were algebraically added to the Yaw Damper inputs.

Airbus documentation indicates that the Yaw Damper is probably compromised in ALT-2 outside the Normal Flight Envelope, and it seems that most of the fight with the rolling could have been prevented if the Yaw Damper was OFF. With low IAS, the lateral stability was undoubtedly compromised.

@CONF iture; I've not been able to find any documentation that indicates that the Outer Ailerons are unavailable in ALT-2, but it certainly appears to be the case.
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Old 29th Oct 2011, 22:26
  #1497 (permalink)  
 
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Thanks mm43 for your research, I was expecting some inputs from Svarin A33Zab PJ2 takata ... but none of them seem to be around lately.

There is still so much to analyze on the little FDR data we've been given ...
Is it possible, the captain, after suggestion from the PNF, did switch OFF both PRIM and SEC 1 ?
Was it done in an attempt to force Direct Law or something ?

The other, you did post something of interest from the Instructor Manual ... By any chance, would you have a link for that manual ?
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Old 30th Oct 2011, 00:58
  #1498 (permalink)  
 
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CONF iture;

Thanks for your comments.

The following link to the A330 Instructor Support Manual will provide some more insight into the design/operational criteria additional to the FCOM.

The on page Search facility in the document works well.
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Old 30th Oct 2011, 01:18
  #1499 (permalink)  
 
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I have been reading something on AOPA online that may relate to what the PF on AF447 experienced.
AOPA Online: Technique: The 'Panic Pull'
The main goal of unusual-attitude training is breaking the deeply ingrained and nearly universal “panic pull” reflex that causes pilots to haul back on the stick or yoke when bank angles exceed their comfort levels.
A multiyear study by Aviation Performance Solutions LLC (APS), an Arizona firm that offers a range of upset recovery courses, found that the pull reflex is especially strong—and particularly perilous—at low altitudes, and it afflicts new pilots as well as seasoned pros.
“An alarming 90 percent of pilots without previous upset recovery experience ‘pull’ when faced with an overbank situation beyond 90 degrees,” according to an APS report. “A full nine out of 10 pilots, regardless of experience level, will most likely pull into the ground in a wake-turbulence upset or cross-controlled stall when faced with the situation for the first time.”
I would expect any pilot who has never flown a slow roll might easily succumb to this reflex. (Not referring to barrel rolls here.)

It might not take a very extreme roll on a black and turbulent night to trigger the pull reflex in an already surprised and anxious pilot.

I don't expect everyone to embrace this concept immediately. Just an idea to kick around.
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Old 30th Oct 2011, 08:57
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Mbird - what is more deep-rooted and more difficult to eradicate is the natural instinct to pull back hard when you see the ground/altitude zero rapidly approaching. Sometimes it works and sometimes.....................

AF447 never got to really 'extreme' bank angles and the 'pull' was rooted in a different mental process.
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