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AF 447 Thread No. 12

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AF 447 Thread No. 12

Old 24th Sep 2016, 08:21
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Originally Posted by Goldenrivett
@ DozyWannabe. I seem to remember that you argued the AoA probes would be unreliable if the IAS indicated less than 60 kts despite being airborne.
Well, I'd imagine they'd be reliable if the vertical airflow in a stall situation was > 60kts, but on the other hand that's a situation that no-one in their right mind would want to be in!
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Old 24th Sep 2016, 21:07
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With respect, I remember it a bit differently. I think the consensus was that in theory it's a good idea, however in the case of this particular accident the crew missed so many cues from the instruments they did have that having an AoA indicator on top of those likely wouldn't have made much difference.
It is too easy to crucify the crew for "missing so many cues"
Instruments were providing confusing informations for the 3 min the airplane was fully stalled.
A simple AoA indicator would have told the true story with consistency from the highest point to sea level. Maybe just what was missing to both copilots and the returning captain to properly analyse the situation ...
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Old 24th Sep 2016, 21:17
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What's so confusing--nose above the horizon, altitude decreasing at a vicious rate means huge AOA problem. An AOA indicator, based on present training syllabi, wouldn't have helped them as they missed the huge clues, why would they have figured with one rather subtle clue?
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Old 25th Sep 2016, 08:24
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There is nothing left to milk the thread except perhaps having one last parting shot. Most have left. Those who are still there nothing will change for them.
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Old 25th Sep 2016, 10:14
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vilas, ' nothing more to milk'; depends what you look for, what you have learnt or are prepared to learn.
Any 'new' aspects may be far removed from the previous discussion on what happened or AoA displays.

However, there is one related aspect of AoA which the regulators / manufacturers may be considering.
Most commercial aircraft use AoA for stall warning and identification; a key area is where these functions are not available. Conventional warning and identification is not required in envelope 'protected' aircraft, but with the unavailability of that protection, the alternative warnings / alerts may not be as good as standard systems, e.g. stick shake / stick push are more effective than a voice call.
Whilst any of these systems might not be available during some extreme speed excursions, they are normally available during the approach to and transition from safe flight to an upset, i.e. the avoidance - preventative functions still work.

The particular issues in this accident were the 'immediate loss of protection', voice stall warning, and no equivalent stick push. These were compounded by trim interaction.
Safety solutions may consider retaining the protections longer during a malfunction, and/or strengthening alternative alerting; enhancements to speed awareness are already in place.

All of the above are preventative, - avoidance; whereas the recent suggestions to use pure AoA displays are reactive.
The reactive approach requires good situation awareness and recognition so that an appropriate course of action can be considered - use AoA display. Unfortunately, as in this accident, if crews have insufficient awareness or understanding to appreciate an audio stall alert or consider attitude to effect a recovery, then a new AoA display may not be any more effective.
Look for the assumptions in change proposals. Also see surprise and cognitive workload as discussed in Emirates 777 thread.

As for other lessons, look further afield. Every day CRM for storm avoidance, UAS checklist and training, methods of simulation, and as to why additional refresher training was required at all; what was the alternative.
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Old 25th Sep 2016, 18:41
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Originally Posted by GF
What's so confusing--
Yes, confusing informations :
  • Nose was also 10 deg below horizon
  • V/S showed also zero
  • And of course when "the PF made pitch-down inputs. In the following moments, the angle of attack decreased, the speeds became valid again and the stall warning triggered again."
It is simplistic to state "they missed huge clues" but you was not there.
If an AoA indicator had indicated they were all the time above 35 deg, I would not call that a "subtle" indication, especially for the returning captain.
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Old 25th Sep 2016, 20:43
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Whether jet-transport pilots should have an AoA indicator or not - and I must admit I'm inclined to think that they should, even if it is only to be used as a last resort for stall diagnosis in the event of loss-of-control following UAS - the issue remains of the perceived validity of AoA indications when the IAS is genuinely lower than that needed for sustained flight.

When the AD design team for Airbus FBW at Saint Martin-du-Touch (?) decided in the mid-1980s to opt for invalidating AoA data at IAS < 60 kt (assuming my memory serves), were they:
(1) just playing safe, i.a.w. normal engineering practice;
and/or
(2) influenced by the assumption that such an airspeed would only be indicated when the a/c was on the ground, and the vanes on either side of the fuselage would therefore be susceptible to crosswind and shielding effects (for want of a better description).

In any case, the possibility of a large jet transport achieving a genuine IAS of less than 60 kt when airborne, even with the grossest mishandling, seems too remote to merit consideration. However, one would have to consider the reliability of the AoA vanes in conditions that had already caused UAS due to freezing of pitot-head(s).
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Old 26th Sep 2016, 07:33
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When the AD design team for Airbus FBW at Saint Martin-du-Touch (?) decided in the mid-1980s to opt for invalidating AoA data at IAS < 60 kt (assuming my memory serves), were they:
(1) just playing safe, i.a.w. normal engineering practice;
and/or
(2) influenced by the assumption that such an airspeed would only be indicated when the a/c was on the ground, and the vanes on either side of the fuselage would therefore be susceptible to crosswind and shielding effects (for want of a better description).

or
(3) abiding by the vane manufacturer's DDP which gave the limits on output validity for the vanes?
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Old 26th Sep 2016, 08:29
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Only thing I don't understand is how AOA display will prevent bizarre application of flight controls which created the need for all that? AF447 didn't have speed but five and half years later after learning everything about it in QZ8501 despite having everything the initial action that started the disaster and continued to the crash was exactly same. With introduction of BUSS you can survive without speed below FL250 provided you don't do something above 250 that makes BUSS irrelevant.
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Old 26th Sep 2016, 10:05
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Quote from Owain Glyndwr:
"or
(3) abiding by the vane manufacturer's DDP which gave the limits on output validity for the vanes?"

Thank goodness for the presence of an engineer to remind one of the obvious! In which case, perhaps the vane manufacturer might be politely asked to reconsider the DDP and/or review the design?

Hi vilas,
I entirely share your reservations about the chances of the AF 447 crew having benefited from an AoA indication that morning. The actions of the PF in making or allowing the a/c to climb from a stable cruise regime were so bizarre that the inclusion of another parameter to those currently available to him is perhaps unlikely to have improved his situational awareness. There remains a slight possibility, however, that the presence of an AoA gauge might have informed the captain of the deep-stall regime that was in force when he entered the cockpit during the descent. Whether there was sufficient altitude to effect a recovery at that stage, given the application of immediate and correct action, has been the subject of some speculation previously.

CONF_iture reminds us of the anomaly by which the stall warning is inhibited when the AD detects an IAS below 60 kt, which may or may not be false. That is something that needs to be addressed.

Another problem is that, on any type of a/c, the trouble with aural/tactile stall warnings is that they remain at the same intensity regardless of how much the stall AoA has been exceeded. I'm wondering if the sudden appearance of an AoA indicator showing clearly how much the AoA is above the stall might be useful.

In the case of AF 447, there would have been periods of stall warning activity where such an AoA gauge could have shown the crew that the stall AoA had already been exceeded by a very large amount. This MIGHT have finally alerted one of the pilots to the developing situation. Whether that would have resulted in his taking the correct recovery action is, of course, another matter.

Last edited by Chris Scott; 26th Sep 2016 at 10:24. Reason: Minor clarifications.
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Old 26th Sep 2016, 17:51
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When looking for possible improvements of the equipment we should look to future and not bring in AF447 because how an insufficiently trained crew would have used that enhancement is impossible to guess.
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Old 26th Sep 2016, 21:37
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With all respect, Vilas, training has almost certainly improved since AF447 data was revealed.

Instrumentation might also have been improved, but the basic cause of the crash was aircrew error. Control inputs were a factor. Stall recognition was a factor. The 'bus FBW degredation modes were a factor. It was a perfect storm.

The AvWeek thread about AoA is a lot less thoughtful than here.

I was and still am convinced that some AoA indication could have helped AF447 even if the sucker had a red flag saying it was unreliable. The jet did not instantly go into a deeply stalled condition, and apparently the AoA sensors were valid until the jet got very slow or the AoA was far in excess of what was designed.

As most here know, ya gotta use all the indicators and sensors you have available.

As one of the AvWeek references makes some good points about speed and AoA, I am here to add to his examples. I had a rainy night landing in my A-7D and once the flap handle was down and the speed versus AoA looked good I followed the AoA bracket and the indexers ( we had the Navy-style HUD). Bad news was that the flap handle had a "beep" function once "around the horn". So you could stop full deployment of the trailing edge flaps. Dunno why, but that night I inadvertantly bumped the handle and my trailing edge flaps were about half or less than desired. The AoA bracket looked good, and the leading edge flaps had deployed per the book. I was going maybe 15 or so knots too fast!!!

I had anti-skid cycling and finally lowered the hook to take the cable at far end of the runway. Lesson learned!!! Cross check all the gauges and there's no serious penalty for a "bolter" whether on a boat or a 9,000 foot runway.

I later flew the first fully FBW jet as most here know. Our AoA display was only there with the gear handle down, although the flight control computers used multiple AoA sensors to keep the pointy end forward all the time.

I really like the AoA for approaches once cross checking with estimate of speed for weight and such. My Sluf barrier exercise made that a rigid entry on the mental check list.

I like the idea of an aural warning of the AoA, but seems the 'bus has a lotta aural stuff already, ya think?
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Old 26th Sep 2016, 23:41
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Originally Posted by Clandestino
Originally Posted by Jimmy Hoffa Rocks
Interesting to note that the FAA places more emphasis on jet upset recovery than in the EASA and in Europe.
Because you say so or you have references?
The FAA mandated upset recovery training in 2010. EASA decided to expand their requirement in May 2015. Article linked below accessible for subscribers describes the recent stall requirement differences between the two regulators.

EASA Opposes Full Stall Simulator Training Upset Training - Aviation Week

Discussed to some degree here.

For those interested in implementation standards and practices:
IATA - Guidance Material and Best Practices for
the Implementation of Upset Prevention
and Recovery Training
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Old 27th Sep 2016, 19:59
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@all

nice to see you guys back, I actually missed you all!
And nothing has changed concerning the individual assesment concerning AOA!

Keep happy!
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Old 27th Sep 2016, 23:53
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Ah yes, flame out the tail, he's in burner; flames out both ends, he has suddenly became very predictable and a target.

Yes, the G6000 with Collins has a small AOA gauge on the PFD, I use it but most guys wouldn't know much about it as the AFM gives zero guidance on recommended AOA readings for specific regimes. I watched the AOA on the C-5 like a hawk in the pattern or when in any unexpected situation, say holding for the tanker at max formatting altitude. I was Board President for the Diego Garcia crew.

Rapidly unwinding altimeter, without a corresponding nose position should be a big clue. Regarding the 60 knot stall warning cut-out, I believe that is pretty common, it is in all Bombardier planes.

OK465

Did you post something on the reaction if an Airbus put into a steepish climb, watch the THS roll nose up and see how it reacts in the sim?

Last edited by galaxy flyer; 28th Sep 2016 at 00:41.
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Old 28th Sep 2016, 07:52
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Without knowing the crew's thoughts, it's almost impossible to understand why the crew acted as they did; any other view is supposition.
However, generic answers might be identified by taking a wider view. We normally act as we see a situation, where perception is an amalgamation of sensed information and that stored in memory. Thus actions can be influenced by how something is sensed and what we have experienced before; this is the basis of training, - how to influence behaviour for future activity.

Thus we might improve our understanding of accidents by identifying potential contributory factors.There is no certainty that these were influential in this accident, but by considering possible effects, then other events might be avoidable.
In this accident. What was simulated, how; how checklists are formed and used, and threat knowledge.

Did UAS simulation just remove the airspeed display; or were all the effects of an ADC system malfunction on other systems accurately represented - the surprise factor - no simple clue to the problem.

Did the checklist have a condition statement before memory items; 'if an emergency then memory items', if not, read the followup actions. An 'emergency' is subjective according to experience.
If the checklist was drafted to differentiate the dynamics of a situation - takeoff, climb, descent, cruise, then the cruise condition would not require memory action, only the followup items. Had that aspect been trained, was the training related to the real threat (ICI), did the crew, simulator, operator know.

Did operational procedures require the Captain (P1) to handle the aircraft in an emergency; thus the basis of the PM's experience was only by reading the check list. Were the followup items considered; shortage of simulator time, handling more important than reading lists. Would a PM gain sufficient experience to qualify as a relief PF, enabling judgement of an emergency, and in handling the aircraft with abnormal feel.

It is difficult to answer these questions based on what has been reported about this accident, but we can look at current activities to learn about what happens now, and perhaps avoid similar incidents.
It is also essential to continue questioning, to consider any other influencing factors.
Why require refresher training for UAS; the threat was ice crystals. It would be more logical to train avoidance of CBs - ICI, radar handling, calculating larger miss distances, threat knowledge; opposed to reactive actions for UAS, which should have already been trained in basic training.

None of this requires AoA; except a gauge of how we think about accidents.
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Old 28th Sep 2016, 09:02
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I was surprised to read in airbus Safety First December 2007 issue a detailed discussion about Unreliable Speed, exactly one and half years before AF447. It included Effects and consequences in the cockpit, Identification and handling of UAR situations, Procedures and BUSS. It didn't seem to have caught anybody's fancy. The crew that night was simply ambushed. It is amply clear that they didn't have the knowledge or training to identify what was happening and apply appropriate procedure. UAR is very serious situation to identify and correct and in my opinion something that was not going to happen by accident. In a habitat that is not human confronted with a situation you feel inadequate can trigger extreme fear leading to hyperventilation which can wipe any semblance of rational thought. What difference another instrument would have made is impossible to predict. Airbus did give a thought to AOA indicator but didn't consider favourably. In a conference in 2010 airbus had stated the following:



Even if the AOA is the key parameter, we do not intend to equip our aircraft with AOA indicator for 2 reasons: first this would require a specific training, and second the stall AOA varies from low to high Mach number so that it is not a constant value.
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Old 28th Sep 2016, 13:19
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AF 447
This was done to me recently in the SIM. I did not know what was coming or what to expect. I probably should not admit to it, since it reveals several mistakes on my part, but for the greater good, here we go.

It was night time. There were no clouds or any weather visible from the cockpit. There was no moon or stars or horizon. The Captain actually got out of his seat; saying he was "going to the loo". After he had gone, I was given a climb from FL350 to FL370. I initially declined the climb, since REC MAX on the PROG page was only showing FL370, however, they insisted, so for the purpose of whatever it was they wanted to demonstrate, I complied. As the aircraft climbed, the airspeed very slowly increased. I thought odd - perhaps an Auto-thrust or speed control fault? Both speed tapes were showing exactly the same thing however, I thought odder still.

I was starting to think about unreliable speed when the over-speed warning went off. I tried to ignore the warning and work out what was happening. Both speed tapes were still identical and steady. The Airbus overspeed warning is extremely loud, extremely insistent, and does not stop (and I forgot how to cancel it). After a few moments of apparently being in overspeed, and the very loud, very insistent warning going, I deployed the speed brakes to no avail. I then pulled the thrust levers to idle. Soon after that, the nose dipped. I thought ah, now I know what they are doing to me; Abnormal V alpha prot. So I followed the OEB for V alpha prot and turned off two ADRs.

This did not help and they froze the SIM with a V/S of -14,000'/min showing.

Now, you are probably all way ahead of me here, but there I was holding full back stick and descending at 14,000 a minute and not understanding what was going on. Sound familiar?

Once they explained what had happened, they released the SIM, and I pitched forward to unstall the wing, added power and safely levelled off.

I was very shaken by this demonstration, in particular how I had ended up holding full back stick having stalled the aircraft.

Several points and recommendations:

1. I did not recognise unreliable speed, or the fact that both the Captain's and F/O's pitots had frozen up simultaneously during the climb. I did not follow the unreliable speed drill.

2. I did not recognise that the aircraft had stalled. This was in the SIM, and there was no airframe vibration or reduction in external wind noise to give clues about reducing airspeed. Nevertheless, I did not recognise the stall, despite the sudden nose drop.

2a. When they froze the SIM so we could see what was going on, I agreed with their diagnosis but said, 'but the audible "stall stall" did not go off'. They said "yes it did". So it was sounding but I literally did not hear the audio saying "stall stall".

3. I, like many at the time of AF447, said that I would never be stupid enough to hold full back stick. But that is exactly what I did - thinking I had a V alpha prot problem.

4. Unreliable speed does not necessarily manifest itself as one wildly fluctuating or stuck speed tape while the other one moves normally - which was the only demonstration of unreliable speed that I had previously been shown.

5. The over-speed alarm is far too strident. It blocks the brain, preventing sensible thought. It should not be a continuous repetitive chime. Overspeed of a few knots is not going to kill anyone, or even damage the plane actually.

6. If the aircraft stalls, there needs to be haptic (vibrating) feedback from the side-stick, like a stick shaker, and all other audio needs to be suppressed except just the "stall stall".

~ According to human factors research, our hearing is the first sense to shut down when we become overloaded. So there needs to be a physical vibrating feedback to alert the pilot, and the amount of audio alerting needs to be kept to a minimum - only the most important thing at any point should sound.

7. It is high time and extremely important that a method of measuring airspeed is urgently developed that is not susceptible to interference or incorrect reading under icing conditions.


I made mistakes during this SIM demonstration and missed cues and clues that I probably should not have missed. But in my defence, I have never seen them in the form they were presented to me. It is one thing to read about failures in a book, but one should really experience the most safety threatening failures. I am not proud about this but I am hopefully a better pilot now. In future, if anything on the PFD ever looks unusual, (or even impossible !), I will take out the autopilot and the auto-thrust and set 2.5 degrees up and around 83% N1 (in the cruise). This will keep us safe and flying normally while we work out what has gone wrong.

I take back anything I might have said about the crew of AF 447.

Last edited by Uplinker; 28th Sep 2016 at 13:29.
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Old 28th Sep 2016, 14:18
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Vert interesting Uplinker, and thank you for sharing.

Originally Posted by vilas
Even if the AOA is the key parameter, we do not intend to equip our aircraft with AOA indicator for 2 reasons: first this would require a specific training, and second the stall AOA varies from low to high Mach number so that it is not a constant value.
1- They still provide some aircrafts with the BUSS that should also require a specific training ...
2- Whatever the Mach, at 30deg of AoA, you're stalled, Top Priority is to urgently reduce it !
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Old 28th Sep 2016, 14:20
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Very enlightening to someone not on the 'Bus. I have a much better understanding of what might have happened that night now and you have removed my prejudices of the plane and crew.
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