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AF447 Thread No. 3

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AF447 Thread No. 3

Old 9th Jun 2011, 17:11
  #1681 (permalink)  
 
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@PJ2

You forgot the first rule of Pprune:

Never blame the pilot.
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Old 9th Jun 2011, 17:25
  #1682 (permalink)  
 
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Blame the pilot

Given PJ2's background, he's totally entitled to do so ... and he is doing it in a very honest and respectful manner.
Airbus' designers are not treated as well by some other contributors ...
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Old 9th Jun 2011, 17:27
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Stall warnings

Stall Warning

In normal law, given the protections available, the stall warning was designed to avoid its activation before those angle of attack protections and not to provide an additional protection. So, this warning is triggered in normal law as soon as the value of the angle of attack of one of the three sensors reaches 23 degrees in landing configuration, higher than the angle of attack associated with Vs1g

N.B.: For a given configuration, Vs1g is the lowest speed at which the aeroplane can develop lift equal to the weight of the aeroplane

In alternate anddirect law,this threshold is modied in order to allow the stall
warning to be set off at a lower angle of attack than that associated with Vs1g

(from Air NZ - Airbus A320-232 ,page 30)

Do these tighter AoA thresholds (in alternate law, along with turbulences) explain why stall alarms (going hand in hand with the revertion to the alternate law) were frequently observed: in 9 cases over the 13 past Pitot incidents ? (analysed in the 2nd BEA interim report).
In the Air Cara´be case, as far as I can remember, the stall warning was triggered for an AoA around 4.3░.
So we get:
-a variable meaning/sensitivity (thresholding) for the stall warnings (depending on the law/mode you are in),
-when the airspeeds become unreliable and when the ADR disagree (triggering the alternate 2 law), this tighter stall warning threshold seems to become a function of the airspeed (not in normal law),
-variable ways to handle the stall warnings (depending whether you read the ECAM messaging "risk of undue stall warnings" or the unreliable IAS C/L urging to consider seriously the stall alarms since they are based on the AoA)
-a stall warning supposedly independant from the airspeeds but inhibited when the IAS are no longer valid

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Old 9th Jun 2011, 17:29
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FE Hoppy;

I wasn't aware that there were "no-go" zones in this discussion. Are we under an informal rule or do we stay true to our craft?

The notion of "blame" is not in play in any discussion regarding the accident.

If people choose to read a discussion this way, that is beyond the control of the contributor who chooses to discuss all aspects of this accident.

Blame has no place in the discussion but examining the evidence available and positing notions and otherwise going where data and evidence and knowledge of the airplane etc lead, is a primary investigative principle, one which, I will add, is not honoured (despite their membership in ICAO), in many countries and in a number of accidents which have been discussed on PPRuNe.

The entire picture of course does not snap into focus - that's what "blame" does...attempts to snap things simply and leave it at that. Instead, bits and pieces are examined, placed aside for later consideration or placed on the table for closer examination or placed in what would be an extensive discussion of factors working in parallel.

That is the kind of discussion I would expect from those who want to "find out" rather than hand it off and "blame the ____".

As a pilot I am keenly aware of the dangers of "blame". I am a flight safety person, not some lawyer with an interest.
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Old 9th Jun 2011, 17:56
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Does a pilot really need a stall warning at <60kts/AoA > 35deg to tell him or her that the aircraft is stalled?!
FWIW:

If the airspeed indicator isn't working, and pilot is on instruments, a possible answer to that is "yes?" (Or, if the AS indicator is working, but the pilot thinks it isn't, and is on instruments ...)
You ask a good question: does that make sense as a design case?

But even if one accepts that as a possible reason to display AoA ... one is still left with an instrument scan, and all of the other cues, none of which are seat of the pants.

What is Attitude Indicator telling you? (Pitch & Roll, turn & slip)
What is Altimeter telling you?
What is VSI telling you?
What is the Thrust/Engine indication?
What is are your configuration display telling you (flaps, gear, etc)

I am still wondering, and will probably not get the answer to:

What did the PF see? Where was his scan taking him?

Hopefully, info from the CVR will eventually reveal what PNF's response was to the climb from FL 350 toward FL 380?

What did he see, what did he say?

EDIT: to make sure I understand correctly

Stall Warning is intended to sound/go off at an AoA less than stall AoA.

Point being (like stick shakers or rudder shakers on various aircraft) to cue pilot to act to prevent the stall. Stall warning would remain on until AoA goes below that value, to indicate either "you are still close to stall" or "you are stalled" either of which is a cue to do something to unstall the aircraft, or get away from the stall threshold. A simplistic way of translating Stall Warning is "change your AoA, it's too high" as noted in various posts in this and other threads.

(Yes, pitch and power remain the basics).
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Old 9th Jun 2011, 18:06
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Without question, the role of bias is part of every investigation. It is a part of every human being who is not perfect. Better it should be established, and weighed (also with bias), than denied, whether naively or slyly.

Commercial carriage is a capital venture subject to the whims of market, but mostly to the realities of competition.

An example, an excellent example, is the Thales Probes. I will apologize for calling them "Junk", but only insofar as it may have offended a friend. Here, there is no argument in evidence that the research and performance were faulty, that these devices should be accorded a benefit of doubt, or other accommodation. They did not perform according to expectation, an expectation that was made with warranty, and involved the possibility of killing passengers. This is not proven. Instead, mitigation in the training of operators was devised, and approved.

How many are then guilty of at least poor judgment, if not criminal culpability? In hind sight, the proof appears stronger than than the "Defense".

"Blame" and "responsibility" are cousins. "Fault finding and Fact finding are brothers.

How distracting does it become that some would excuse the "discipline" by saying "we don't do this"? No one is excused, and if feelings are ruffled, that is a good thing.

People are dead, and thus far, it is becoming clear that no "Act of God" is responsible, and some may be responsible in some way for these terrible losses. In my opinion, it is a good argument that preserves the emotions in play here.

My bias is a matter of record. The worst thing that could happen is for this accident to fade. In its loss of currency and care would be the continuation of a way of "doing business" that is repugnant to those who care about people before profit.

Does this happen? Can we change it? I do not know. But if we give in to the pressure to keep the current methods in play, these souls will never forgive us.
 
Old 9th Jun 2011, 18:19
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Wolf

you ask.... ".....What did the PF see? Where was his scan taking him..."

BEA..... "...The PITCH progressed beyond ten degrees, and the a/c started to climb......" (emphasis mine)

I haven't seen data re: AoA just prior and just after a/p loss. Pitch and power, if accomplished would have established a Pitch of far less than Ten degrees, (more like 3.5). So Pitch was not, and did not become, compliant with UAS procedure.

That is it. BEA has the rest. The fifteen seconds on either side of loss of a/p are the meat, the rest is potato. Clearly, the danger to flying passengers has been determined to be within limits, if not the actual data of this accident?

Plenty of time for a measured and patient response from the authority, then?
 
Old 9th Jun 2011, 18:25
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Originally Posted by Lonewolf_50
What did he say?
As an answer to all of the posters insisting on the CVR content....

What would you have said ???

Unlike some well-known tennis players, yelling/shrieking at every stroke, I doubt the average pilot in such a situation would have punctuated his every action with yells and shrieks and expletives (except for maybe the occasional "putain" and "merde".....).

CRM does not always equate to being able to give an intelligble running commentary for your colleagues and the CVR... esopecially if you're confused yourself.
It's not tennis.....
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Old 9th Jun 2011, 18:30
  #1689 (permalink)  
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LW_50;

Regarding what the PF saw..., CONF iture asked the question a while back about whether the QAR would have the CAS parameter displayed on the F/O's PFD.

There is no easy way to answer the question for, as discussed in the post on data frames, QARs are different animals and are subject to more variations in what they record and how they record it (in terms of rates). The parameter is certainly available and, optimistically, I would think it would be on the QAR, which of course is primarily used for FOQA/FDM analysis by the airline's safety department. A lot of other stuff will be there as well and being solid state it may have survived even in water.

We can't say for sure whether the three airspeeds failed in the same way because we don't have the data. But I think they did fail the same way. I think it was gums posted an A300 manual's schematic page which showed very clearly what happens downstream and over a short period of time to airspeed indications when the pitot head or drain holes are plugged with ice or water. It is more difficult to imagine differences than it is similarities although until the data is available, it is possible.

What would cause the ADRs to read a higher speed and send it to the DMUs which display same on the F/O's PFD, that permits at the same time, the loss of airspeed on the Captain's display and the ISIS, and the uniform increase in AoA parameters to 16deg and beyond?

The questions concerning the attitude, sideslip, altimeter and IVSI are good ones, and we need to understand what else the PNF saw and perhaps said. None of us here expect that this release was not closely vetted.
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Old 9th Jun 2011, 19:07
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As a basic watch this or die type indication, something calibrated to the specific aircraft in the form of the old F4 indexer lights could be an answer to the crew getting swamped in a high stress situation.

Not the dual bulb shoot light on the right

OR



OR



Something simple and mounted away away from a confusing/failed/corrupted lcd display.

just my 10p worth, nomex applied.

Last edited by glad rag; 9th Jun 2011 at 19:28.
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Old 9th Jun 2011, 19:34
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gladrag, isn't that AoA indexer only activated when the gear is down? (Memory faulty on that one ... maybe that depends on aircraft model ... )

Bear:
Wolf
you ask.... ".....What did the PF see? Where was his scan taking him..."
BEA..... "...The PITCH progressed beyond ten degrees, and the a/c started to climb......" (emphasis mine)
bear, I didn't ask what the FDR recorded, I asked what the pilot saw. Not necessarily one and the same. I am asking what had his attention. A scan can turn into a boresight under stress.

ChristiaanJ
What would you have said ???
Hard to say. Were I a copilot, and I saw the pilot climbing, and we were at a phase of flight meant to be straight and level, and he hadn't told me he was going to climb, I suspect I'd have said: "You are climbing." Maybe "Do you mean to be climbing?"

Even more likely, had I seen the climb, (and assuming AF SOP is similar to an old outfit of mine), I might have said, "Two hundred feet high and climbing" since assigned alt was FL 350 ...

But that's a guess.

I don't know what PNF was looking at. I've no idea what cue first caught his attention of something in the flight profile being "not quite right."
Unlike some well-known tennis players ...
I was thinking more along the lines of some standard CRM and copilot functions, not a Hollywood style set of emotive statements. Nor a grunt. (PS, pet peeve of mine, all that tennis grunting ...)
CRM does not always equate to being able to give an intelligble running commentary for your colleagues and the CVR... esopecially if you're confused yourself.
It's not tennis.....
I know it isn't tennis, having flown in mutiplace aircaft. I am not asking for running commentary. I am keenly aware of how little one says when one is catching up to an aircraft. (Been there) Maybe he said almost nothing.

I am interested in what cues he did, or didn't, respond to in executing copilot duties in support of his pilot.

What he said (as recorded on the CVR) may give a clue at which things in the cockpit he was looking at, and which things he brought to the attention of the flying pilot.

Or not. (You make a very good point! )

PJ2
LW_50;
Regarding what the PF saw...,
The parameter is certainly available and, optimistically, I would think it would be on the QAR, which of course is primarily used for FOQA/FDM analysis by the airline's safety department. A lot of other stuff will be there as well and being solid state it may have survived even in water.
Yes. My question includes "of all the things in front of him, what most caught his attention, or what group of things did he pay attention to?" He may or may not have communicated to his copilot what he did or didn't see, or what was his main concern, beyond "alternate law" and comments on the speeds that have been released ...

I have myself, while on instruments, had the whole instrument panel in front of me but had my world collapse into a form of tunnel vision where all I could "see" was attitude indicator, airspeed, VSI and Altitude ... barely heading ... I had to force the scan around ... as I fought vertigo. You could have asked me power setting and I'd not have been able to tell you, as I wasn't seeing it, it was where I had left it. You could have asked me AoA and I'd have had no idea.

The questions concerning the attitude, sideslip, altimeter and IVSI are good ones, and we need to understand what else the PNF saw and perhaps said. None of us here expect that this release was not closely vetted.
Aye.
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Old 9th Jun 2011, 19:58
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Cool

Hi,

PJ2

the airplane was stable before the event and, doing nothing while the airspeeds return will keep the airplane stable. Move it, and you've moved the one "known" in the equation that you had and you've taken yourself into no-man's land with no way back, without a great piece of luck and skill.
This does not seem to be the case so I just re-read the note from the BEA.
And my doubts were founded.
When the autopilot disengaged (for any reason whatsoever) the aircraft banked to the right.
What happens if the pilot does not correct this inclination?
The aircraft was stable before the autopilot disengaged:
Sure .. the aircraft was stable .. but why ?
Because the autopilot was making the adjustments necessary to maintain stable flight of the aircraft (his duty)
When the autopilot disengaged .. it was the pilot duty to maintain a stable flight of the aircraft ...
The aircraft banked to the right .. so ........ hands off ?
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Old 9th Jun 2011, 20:22
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My inclination is to say that the a/c was likely not well trimmed, and was only "seemingly" in stable flight, perhaps "hunting" a good deal. Whatever the cause of a/p quitting, UAS or turbulence, the a/c itself made the decision it was not "stable", nor could it be stabilised (by the a/c). This makes a comment like:

"...the airplane was stable before the event and, doing nothing while the airspeeds return will keep the airplane stable. Move it, and you've moved the one "known" in the equation that you had and you've taken yourself into no-man's land with no way back, without a great piece of luck and skill.."

quite patronising, and dismissive of a very likely reason for not "sitting". Also, perhaps a bit biased in favor of the "Platform".
 
Old 9th Jun 2011, 20:27
  #1694 (permalink)  
 
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Originally Posted by jcjeant
When the autopilot disengaged .. it was the pilot duty to maintain a stable flight of the aircraft ...
The aircraft banked to the right .. so ........ hands off ?
Yes, would probably have been the better choice....

It is hardly conceivable that this roll momentum would have been so violent that they would have ended upside down within seconds.

And then a more careful reaction (with less potential for over-reaction) would have been to trim the rudder to compensate for the roll. Especially since a rudder mistrim is a premier candidate for being reponsible for the roll in the first place. A strong fuel imbalance would be really strange. That normally does not happen. At least not without a prior warning of a pump failure or similar. And that you would have found on ACARS. So I would consider that highly unlikely.

Knowing that it is really hard to fight the urgency to do 'something' if something unexpected occurs.

Edit:
@PJ2: Thank you very much for your rational and well balanced and informed posts !!!

If one wants to learn something from this tragedy it is vitally important to keep an open mind. Even if it would mean that the Pilots in this case made Errors that mainly caused this accident.
And if it was that way it must be allowed to say this here otherwise it is not worth the discussion.
As PJ2 and others have said: This is to improve safety and not to put blame.

Last edited by henra; 9th Jun 2011 at 20:39.
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Old 9th Jun 2011, 20:33
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(From PJ)
The FWC [Flight Warning Computer] activates the audible stall warning. All other aural warnings are inhibited if a stall warning is in progress.
Design point to consider with this in mind: if airspeed is unreliable, or if AoA is on the fritz, other warnings (engines, for example, if icing is the condition driving airspeed awry) would be useful and even necessary. Establishing a heirarchy makes sense if you are to avoid sensory overload in the cockpit.
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Old 9th Jun 2011, 20:49
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Wolf

I am not persuaded that the A330 needs additional design work. This accident is I believe, more basic than a hugely anomalous glitch might infer.

I don't think BUSS would have made much difference, nor the addition of steam gauges as "back-up".

Credit where due, this a/c did climb with X energy, and reached X-y somewhere near the apogee of a long curve to the Ocean.

I truly believe that the answers are few, easily connectable, and straightforward.

I honestly don't believe BEA parsed the data to "set-up" the pilots.
There is sufficient responsibility available for all, and eventually, it will out, to a very fine accuracy.

I think what we have here are Blunders, not cheese holes. If, in identifying these shortcomings, a new and improved way of driving the Bus (and other a/c), is proposed and accepted, fine.

I also believe that underneath the Blunders will be some of the less attractive aspects of Human behaviour, not limited to Flight crew, by any means.

The Bus was built by humans, and flown by humans. So, not necessarily PE, but H-E.

I would not want to inhabit the moccasins of those responsible for making this horrible crash likely, rather than remote.
 
Old 9th Jun 2011, 21:05
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Laws, functions, protections, limiters

Sorry if I appear to harp on "too many" laws. It comes from reading and examining all the Airbus manuals I have gotten courtesy of this forum. And I thank you all.

I am gonna take a pic of the FLCS ( flight control system) I flew with back in 1979 and you will see many "laws". Will post it soon. The "laws" were those small graphs of impact pressure versus control deflection, body rate limits, AoA limits, etc.

I am also gonna show my problem with all the "modes" and "laws" and "protection". Let's face it, I flew a very simple jet and it had vastly different operational requirements.

That being said, we never used the word "protections". We used "limits". Maybe it was psychological to provide we dweebs some reason that our piloting skills were relevant, but it worked. Heh heh.

Before I take the pics and upload them, I am compelled to comment upon the THS mechanization. I know, one mo' time Gums, when will you let go? Nevertheless I feel it is more important than the pilot action to correct a roll after the AP disconnected.

With unreliable airspeed (think impact pressure, dynamic pressure, CAS/IAS), I look at some of the alternate laws and still see clues that the confusers are trimming the THS. So without airspeed, the jet is still trimming to maintain one gee. It does not care about the pilot aft stick input other than to keep the stick deflection about the same angle regardless of speed. How does it do this? It uses the accelerometers that are the major players for the basic control concept of a gee command versus an AoA command system. You don't need airspeed for the accelerometers to work. Same for body rates. Saw this on one of our accidents when a pelican wiped out pitot tubes, hemispherical air data gizmo and AoA vanes.

So a constant, even a small aft stick, that is commanding maybe 1.1 gee could result in the confusers increasing the THS angle to maintain the same stick angle for the commanded gee. No air data required. This might explain the THS increasing angle.

REMEMBER: The pilot is not commanding an AoA or pitch rate or attitude. The final command to the control surfaces utilize some of those inputs, but the primary output is related to gee. Clever addition of AoA, speed, body rates and such can make the jet "appear" like the last one the pilot flew. But down deep, the control laws are very different.
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Old 9th Jun 2011, 21:33
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Bear
I am not persuaded that the A330 needs additional design work. This accident is I believe, more basic than a hugely anomalous glitch might infer.

I don't think BUSS would have made much difference, nor the addition of steam gauges as "back-up".
1. If you are referring to my post on why you'd clip an AoA input, it was a defense of clipping AoA signal, as currently done, based on the audio warning heirarchy that PJ2 pointed out. This is a different tack than my earlier "why is AoA clipped below a given speed?" query. It made no sense to me to clip AoA signal below a given airspeed. (I suspect that discussions on that point were non trivial in the design process). The warning heirarchy provides some of the reasoning behind that design decision. There was doubtless other reasoning involved.

2. BUSS seems an interesting approach to a problem. No skin in that game.

3. Would an AoA gauge (steam or digital cockpit display) have been incorporated into the scan in this particular instance (and when would that have been practiced in the training syllabus?) ... my guess is that at least one scan got narrow pretty quickly ... but there's something more basic here.

If you don't train for a stall recovery on instruments (for reasons previously explained, to include sims that can't replicate it), what does a pilot finding himself in a stall have in his training background and experience to draw on in order to redirect his scan. His task chain requirement at that point, when stall is identified, is to change his instrument scan from
"flying and getting this bird to the airspeed and altitude I want" scan
to
"recover from stall in the goo" scan
to
"recover from unusual attitude (unstalled)" scan
to
"get back on course, speed, and altitude" scan.

The first scan, not trained, has to be made up on the fly.

Some of the folks here have for two years pointed out that you train to prevent a stall. There are some good reasons for that philosophy, given training limitations. The pitch and power refrain has been sung, like the Hey Jude chorus, since about June 2, 2009.

Considering what training can't be done, see sim limits, that song is number one on the hit parade of the remedy concert to be performed in due course ... but it won't be the only song to be sung.

Still chewing over gums' point on using g to direct control surface positions.

Last edited by Lonewolf_50; 9th Jun 2011 at 21:47.
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Old 9th Jun 2011, 21:51
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I'll show you mine, you show me yours

Sorry for poor pic, but I don't have a scanner and didn't wanna drive down to the UPS store.

The graphs at top are the "laws", or functions. lower right are stick pressures versus gee or roll rate.

I can do it better if anyone cares, but I would really like to see a similar graphic for the 'bus in any of the "modes" or "laws".

Note that in the upper middle we have the "standby gains" for when air data was deemed unreliable. So those values were applied to many functions for control surface movement and rates. I see no such concept/implementation for the Airbus. Why is that?

The left side of the page I used has much more detail, but I need to get a good PDF scan to show how all the functions are added/divided/integrated etc.

We didn't have all this in our operating manuals. I only have it as I was the Chief of Academics for the first training squadron and had to answer questions from the dweeb students, heh heh.

enjoy,

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Old 9th Jun 2011, 22:03
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Originally Posted by Lonewolf_50
Heh. Given that landing speeds of most transport category aircraft are well in excess of 60 knots (A330 looks to be 135-145kts, depending on weight and other conditions) an aircraft in that class with a stall warning at 60 kts below 1000 feet has been in deep manure for too many seconds, and has most likely been gettting stall warnings since long before that ...

Which makes me understand why clipping it at sixty might seem to make sense in the design process, but that seems to indicate a design assumption:

That stall will be triggered at low speed and low altitude? (I may not have successfully reverse engineered the thought process on that one ... )
That's why I'd NOT turn off the stall warning of there is no weight on the wheels. I'd add an altitude test if there's a reliability problem with only using weight on wheels.

Then it may be wise to enter the inertial reference's output into the equations at least for short term stall warnings. Then maybe train in a 10 second or 15 second wait before acting on stall warnings at cruise altitudes.
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