dinbangkok

First up - I'm a regular member of the SLF community. The closest I can claim to understanding the intricacies of what happened on AF447 other than as a layman is a psychology degree (from Manchester University when a certain Swiss cheese theory Jim Reason was at the helm of the Psychology Department). I've been following the discussions on here since the incident in 2009 - thank you for everyone, irrespective of what side of the fence you're on with regard to the unending man vs. machine automation debate. It's been illuminating, fascinating and reassuring to see the unfortunate event dissected and debated by professionals from all walks of life. One hopes that through debates like these, things can only get better.

So my tuppence for what it's worth... From my understanding of the report (which I think overall reads as thorough and even handed), clearly there were some issues in terms of BOTH crew resource management and ergonomics in times of high stress, but the thing that screams out to me as fundamentally wrong in terms of 'how can this be!', is on page 192 of the report: The copilots had not undertaken any in-flight training, at high altitude, for the “vol avec IAS douteuse” procedure or on manual aeroplane handling I find that fact absolutely terrifying - irrespective of how automated the plane is I would have thought that advanced manual airmanship skills should be mandatory for any commercial pilot, irrespective of altitude!. Indeed I can't help but notice a correlation between the well publicised potentially fatal incidents which have been averted, thanks to the fantastic skills and experience of the pilot. Notable of course (and a completely unrelated incident), is of course the one on the Hudson where the pilot was a keen glider. Everyone travelling on that flight was obviously very lucky to have that particular pilot at the controls, but surely we should be looking to reduce the role of 'luck'. But what do I know...

So my question for the pilots out there: Could airlines ever be persuaded to go back to basics and do more to boost the manual flying skills of commercial pilots, irrespective of the level of automation on a designated aircraft?... Indeed completely change the structure of training so that when training on a specific aircraft, pilots start 'manual', with automation added, layer by layer? (adding layers to the onion so to speak)... Ultimately, so that every pilot is confident (relatively speaking), and knows what it feels like, to fly said aircraft when controls / automation have gone t*ts up?

Excuse my ignorance and sorry for interrupting - I'll continue lurking for now. Many thanks again for everyone's contribution

HazelNuts39

There were substantive changes to that paragraph. It is entirely possible that deletion of the words 'througout the demonstration' was thought to be editorial, non-substantive. In any case, those changes had nothing to do with AF447.

Perhaps the condition that all three AoA values are NCD while the airplane is in flight should be considered a failure of the stall warning system:

henra

Hmm, I'm afraid you might be quite on the mark with this objection. This could very well be the reason why they implemented this less than ideal solution.
Circumnavigating the ADIRU in certain instances while going through it normally might open up new cans. (Additonal mini ADR required with possible discrepancies to main ADR's requiring redundancies and another Error Handling logic...)

From a boolean perspective a solution seems possible and even not too complicated but it might indeed conflict with their basic system design necessitating less than ideal workarounds causing other trouble.
Will be interesting to see if, when and how they can fix this.

I seem to remember that Boeing does have a similar logic of suppressing the warning if the speeds are too low. Anyone any idea if they are working on that topic as well?
Do they also calculate SW behind the ADR modules (which normally makes a lot of sense as you would otherwise need an additional mini ADR unit to convert the Raw data in a usable format just for the Stall Warning alone).

Peter H

infrequentflyer789

You can't just fix the SW logic, in any meaningful way.

I beg to disagree, see post #213

The input data simply isn't there in this scenario.

Yes, you do not have a meaningful value for AoA (here represented by a NaN), so cannot use it in a context-free rule to indicate if the stall-warning should be sounded.

You could maybe give the SW memory so it uses last-valid value, which would catch the 447 scenario - but that adds complexity and failure modes there.

As you say, remembering any previous sensor value (e.g. AoA ) leads to extra complexity and failure modes.

However holding the current state of the stall-alarm would not introduce such problems.


In "IEEE FP speak" my AoA_trusted and your AoA are related by: AoA_trusted = NOT(isNaN(AoA)).

Turbine D

Indarra,

IMO, the role of the accident investigation authority (BEA, NTSB, etc.) seems to be misunderstood at times. Their role is to investigate accidents with the sole objective of improving aviation safety. To do this they:
- Obtain and assemble factual information regarding the accident
- Analyze the factual information
- Reach a conclusion on findings of the cause or probable cause
- Make safety recommendations.

Now granted PJ2 and Dozy did some SIM work to look at whether or not recovery was possible (it appeared to be) and Owain Glyndwr did analysis depicted in graphical charts which indicated recovery was theoretically possible. However, this is not information that can be construed factual unless actual flight trials were conducted in an A-330-200 aircraft to support/confirm the theoretical findings of SIM and analysis. For example, the AA Flt.191 out of ORD went down in an asymmetrical stall shortly after liftoff. The NTSB never addressed if the plane could have been recovered satisfactory but concentrated, based on factual investigation how the accident got to this point in the first place. Afterwards, at least two university studies concluded the plane was recoverable. However, approximately 30 pilots when confronted with the problem in a SIM failed to recover the airplane. This is why speculative information or theory based information shouldn't enter into a failure report out, it could be right or it could be wrong.

Digital verses Analog - Well, take a look at the NW B-727 accident during climb out of JFK on December 1, 1974, also a stall accident. In this accident the analog altimeter didn't help either. In fact, I wonder if, at that time, digital altimeters were available, if some people would have concluded a digital altimeter would have helped.

Just some thoughts to consider....

Owain Glyndwr

100% with you

Hazelnuts
As I said, it maybe just me, and it's certainly not worth a lot of discussion, but regardless of whether they intended it to be just editorial, for me, as a one-time designer, that editing changes the S/W duration requirement from conditional [i.e.linked to a prescribed demonstration technique] to mandatory without explicit or implicit time limits. But as I said its not worth an argument.

I don't really see why the logic that AoA vanes are not reliable below 60 kts should have any effect on problems with untoward stall warnings near lift off. Unreliable AoA signals because of dynamic effects yes, but that is a different problem.

With my interpretation of CS25 if it is flying you believe the AoA signal(s) and latch the S/W until the AoA comes back below the threshold and is confirmed to be so. Airbuses have a logic that changes the laws from ground to flight modes, so why are people debating complicated 60 kt and WoW combinations?

Lonewolf_50

Turbine D: Well said!

mm43

Just as a matter of interest and to get away from the WoW debate; does the AoA < 60 KT actually represent unreliable AoA vane angles at sea level or maximum service ceiling? I have feeling it may well be the latter.

Any takers?

PJ2

Turbine D, Re, "Also 100% with you!

Re your earlier comments on the differences in our own sim stall exercise and the way AF447 was handled, yes, ours was a far more brisk pull-up and the comments you and BOAC offered ring true.

Lyman

mm43. Are you saying that the actual AOA may have been greater than 45 degrees? Perhaps much greater?

Diversification

In one of the the preliminary reports it was hypothised that this msg was caused by an attempt of the pilots to shut down one or both of the affected computers.
"02:11:55 - .1/FLR/FR0906010210 27933406EFCS1 X2,EFCS2X,,,,,,FCPC2 (2CE2) /
WRG:ADIRU1 BUS ADR1-2 TO FCPC2,HARD
"
Now the data should be available to either refute or verify this assumption, but I have not found anything about it in the final report. Did I miss it?

Regards

Machinbird

Just a reminder that way back, I did a test with an airline type AOA vane using the hand out the window trick in my car. It came alive at less than 20 mph!

They really don't take much wind speed to activate. 60 Knots might relate to reliable airspeed measurement issues. The key issue is that AOA data is valid in its own right and should never be controlled by airspeed as to whether it is considered valid.

As we see with AF447, they had well over 100 knots airspeed on the way down, it just wasn't being directed into the pitot tubes.

NeoFit

Machinbird

With all respect due, your "hand out the window" AoA car vane test was'nt done witht a -50 degre TAT.

However, I agree.
It's seems to me that AoA vanes effective range is plus or minus 50 degre
(AFAIR).
(and I am sorry coming back with Tarom 1994 event: the plane was stalling with a quite vertical attitude, but the recorded AoA was 'only' 45 degre. Sure, real AoA was out of range).

Best regards

HazelNuts39

It may be more a question of accuracy than of reliability.

mm43

Or is it the angle at which valid CAS is no longer calculated?

Machinbird;

Thanks for reminding us about your experiment. I know the original reason given for the AoA vane invalid @ < 60 KT was to prevent spurious SW in the approach and departure regimes, but it has now been demonstrated to be confusing when the envelope gets "extended".

HazelNuts39

Say again???

mm43

I certainly cocked up that question!

I actually meant that when CAS of < 60 KT was calculated, the ADRs deem that the AoA vane angle can no longer be relied upon. In other words I answered my own question.

HazelNuts39

Lyman,

At the end of the recording the flight path angle relative to earth was -45.2 degrees, and the pitch attitude was +16.2 degrees. In still air those values would correspond to an AoA of 61.4 degrees. With a tailwind component of 24 kt the AoA could have been about 70 degrees.

bubbers44

Does everyone agree that at FL350 when they lost airspeed and autopilot they should not have pulled up to a 14 degree deck angle and stalled the airplane? If they hadn't done that and had done what any experienced pilot would do and hold attitude and power and get appropriate UAS check list we wouldn't be discussing this now.

If they did stall at 38,000 any competent pilot could recover from a stall and not crash unless for some strange reason he thought holding full or almost full back stick would help him recover. Please tell me no pilot here would do the same thing they did.

john_tullamarine

If they .. had done what any experienced pilot would do and hold attitude and power and get appropriate UAS check list we wouldn't be discussing this now.

Probably we are all agreed on that point.

any competent pilot could recover from a stall

One might hope that such would be the case.

However, there is, at least, one caveat (and I note I have no background on the Airbus flock).

While some of our number have had the opportunity to experiment in sim exercises with an indication that recovery might have been possible, we note that the beloved sim is a computer not an aeroplane. The observed sim characteristics are only as good as the aeroplane model programmed and this in an area of the envelope where the model would be expected to consist of extrapolations rather than hard FT data.

There remains the question of just what real world (stability) characteristics the particular aircraft might have had in the circumstances, hand flown at high FL without the computers' assistance. The CG was fairly aft at around 29% (as I recall) and recovery from a deeply stalled situation may have presented a crew with some unusual or unexpected problems. While many may censure the crew and the particular operator's training systems for getting to the stalled situation in the first place, it may be appropriate to cut the guys in the hot seat some slack so far as "oh dear (or words to that effect), what do we do now ?" might be concerned.

Different matter for an experienced experimental TP but we are talking about two line F/Os who (so far as I am able to divine) had no broader experience. Indeed, there are some very experienced TPs who frequent this place and, with any luck, we may get some pertinent comments from those good folk.

Ultimately it will be interesting to see if AB provides useful guidance on the matter ?