I think D P Davies in his classic book "Handling the Big Jets" (written in the 1960s but still has some great guidance) states that the probability of an actual stall in commercial operations was one in ten million (or was it one million - would have to check?) but the probability of a stall warning was much higher at one in 100,000.

Obviously it is important that pilots know how to recover from a stall but far better to prevent the aircraft from stalling in the first place. Notwithstanding stall warning systems this requires a knowledge of the a/c performance and also correct monitoring of vital parameters such as pitch attitude, airspeed, power etc.

If you see ten degrees or more pitch up at cruising altitudes in a swept wing jet transport you better start making a correction before you get a stall warning.

Even before an a/c stalls and/or the stall warner operates (assuming from level flight or thereabouts) the first warning signs are low and reducing airspeed, high nose attitude and reduced control effectiveness.

One thing I dislike about the Brand A use of a verbal "STALL, STALL" (instead of a stick shaker) is that humans have a tendency to filter out aural inputs when concentrating or highly stressed. Meaning the STALL warning may not even be heard when it's most needed.
Problem is, I'm not convinced that a stick shaker is much better - I can think of at least two Brand B crashes where the pilot pulled back in response to an erroneous overspeed indication and stalled, then apparently dismissed the stick shaker as 'Mach buffet' due to the perceived overspeed.

In normal law not in an FBW Airbus.

silverstrata;

The accepted definition of the "deep stall" or "super stall" is that of Davies', which refers solely to the blanked T-tail designs.

Sorry, Austra, why?
Your statement as it stands is tantamount to an ad-hominem, and I don't like abuse. Please explain yourself further.

Icepack, quite!

Ummm... whilst your conclusion might be true, I am not so sure how well it would work with, say, a Stall Warning on takeoff?

"Stall Warning on Takeoff" is an A320 Memory Drill, and taking the power off I cannot recall as part of the drill :ugh: In fact, the complete opposite is the case ;)

Disagree - at the first hint of a stall, he just kept pulling back. As others have said, there is not much thrust / couple at cruise Altitude.

No.

A deep stall is any stall that cannot be remedied with elevators.



When it was identified in the 1960s that rear engined T-tail aircraft could enter a deep stall, stick pushers and shakers were added until it was almost impossible to enter that condition.

We now have a situation where underslung engined aircraft can also enter a deep stall, if the thrust remains at cruise or higher. And this applies to both Airbus and Boeing designs.

In normal law, an Airbus should never enter this state, but in alternate law it certainly can (as can Boeing twins). There is no reason why a stick pusher or a thrust reducer cannot be applied in these cases, where the aircraft is in alternate law. A thrust reduction at the point of stall, will lower the nose quite sharply (if the stick is neutral or forward of neutral) and make the exit of the stall relatively simple.

Aluminium shuffler, while I agree with you regarding thrust at high altitude, how can the following post by silverstrata be explained?

Is it a case of lack of sim fidelity or is elevator effectiveness reduced at high altitude by approximately the same amount as the available thrust is reduced?

Nigel the latest stall drill in the QRH states--


NOSE DOWN PITCH CONTROL APPLY
This will reduce angle of attack
Note:
In case of lack of pitch down authority, reducing thrust may be necessary.

Agreed, but then so would a stick pusher be inconvenient at that point in the flight - but that did not stop stick pushers being added to aircraft. And the last stick pusher I had was quite forceful - ten kilos of push perhaps? Anyway, it was nearly capable of taking the stick out of your hands if you were relaxed.

Likewise the stick shaker which I had go off on rotation, that can be disconcerting too (especially on a 2,000m runway). Am I at the right speed?? Gets the ticker ticking.

Besides, it is not beyond the ken of Airbus engineers, to put a 2,000 ft altitude limitation on the proposed power-reduction-at-stall protocol.

Two factors.

Firstly, this was a stalling demonstration in the sim, so the aircraft was very slow. We might have been back at .62 mach or so, or about 180 kts IAS at 39,000 ft. Remember that with underslung twins, the thrust can overpower the elevator at low altitudes. Yes, there is less thrust at altitude, but that thrust is still opposing the required elevator motion.

Secondly, it is not simply the lack of elevator authority, but the stick forces required (not Airbus). The force required to push the stick forward was surprisingly high and counter intuitive. Normally at altitude the stick is very sensitive, so the need to push with both hands was not usual for that altitude, and could be confusing.

And that is why we do these demonstrations in the sim.

Oakape, I have done the high altitude upset exercises several times in the 737 800 sim and not found any issue regarding flight control effectiveness. The force needed on the elevator will be large if trimmed nose up (for the reducing IAS prior to stall), but that is no different from at any altitude, but even without trimming, I didn't find any problem. I'm not a sportsman and never go to the gym, though I'm not a couch potato either - I just live an active lifestyle. So, a 5' waif may have trouble, but the average male pilot shouldn't have any issues. I can't speak for other types, though.

The Ancient Greek:

My guess at why several stalls have been maintained or exacerbated by pilots hauling back on the column/stick is that it is human nature when scared to grab and pull tight. However, it does show that these individuals and many, many more don't have the appropriate training or experience to overcome that primal instinct. I think removing spinning and aeros (or at least reducing the amount done) and reducing the stalling exercise amount in licence training (at all levels from PPL to ATPL) is a big mistake. I can't help feel that a large amount of training at the edge of the flight enveloppe would sharpen trainee's handling and hone the correct reflexes.

Tdracer - I understand what you're saying about the aural stall warning in 'busses, and agree. Unfortunately, its not possible to fit stick shakers in those crappy little side sticks. I like the idea of a side stick, but I'm horrified that they have no feedback of any sort from the autpilot or other stick. That is a lethal design flaw. I will always be convinced that it is a principal factor in both the relevant accidents and will kill more people yet because the pilot who understands what is happening to the aircraft doesn't realise what the other pilot is doing to the controls, assuming basic competence of not holding an ac in the stall.

Do bus pilots agree that given the amount of publicity hiven to these two accidents, that they should be able to identify and correct a high altitude stall?

Can further accidents of this type be prevented by vigilance alone?

@ physicus...
 

Thank you for that link on the Boeing/Airbus stall presentation it was very interesting.

I only wish we could have a similar presentation for T tail/aft mounted engine aircrafts (which I fly) to see the differences.

It was interesting to hear them say that under all stall condition a "lowering of the nose" was mandatory to reduce AOA, that you should not roll out and lower the nose of the aircraft at the same time (overstress the tail) but lower the nose first then roll out of the turn and finally not to increase the power but wait until establishes in the recovery prior to slowly increasing the power.

Finally it seems that Boeing with its 787 was moving toward Airbus' philosophy when it comes to FBW.

That statement of yours is imho misleading and does not reflect the correct procedure. A neutral stick in the bus commands a loadfactor of 1g, and would therfore force the aircraft in a decreasing speed environment due to power reduction in a higher AOA, the elevators and the THS may drive all the way nose up to achieve the commanded 1g. Same would happen with slight nose down input, as the increasing rate of descent in a stall would be felt by the sensors as less than 1 g, and the commanded g by a slight SS forward might be bigger, thus still the flight surfaces would be positioned for a nose up flight path. With such SS inputs the aircraft would be forced deeper into the stall and into high AOA. Bonin demonstrated how it would end. I'm not saying it might not drop the nose finally, but it might do it only in a very high stall state. And such a mistrimmed aircraft with the elevators and THS all nose up will be a definite handicap during recovery. It may even be the recipe for secondary stalls, as the increasing speed after a possible nosedrop could cause a pitchup again if not countered by manually trimming nose down and using amounts of SS forward to counter it.

So wy would you let this happen in the first place?

There is only one correct stick position as early in the stall as possible concerning the SS and especially in a flightpath stable aircraft like AB: Put the SS forward (and i would even say full forward) until the AOA is reduced to normal values and speed has reached flying airspeed.

We discussed that in the AF447 thread quite extensively, but this misjudgement of the effects of the flight computers under C* striving for the SS commanded g on the elevators and the THS trim from AB qualified crews is astonishing or even alarming.

1. Current simulator modeling DOES NOT give an accurate replication of jet airliner stalls, especially at high altitude. Both Airbus and Boeing say stalls in the a/c are more violent. They've recently agreed to a simulation model that works for n/b a/c (but not w/b's) that we might get to experience in a couple years.

2. You'll rarely see more than 5, or perhaps 6, degrees NU in an airliner above FL300. You need a v/s of greater than 2000-2,800 FPM to see pitch attitudes that exceed 5-6 degrees NU.

Stick Pushers and DP Davies
 

Davies did a long writeup on the certification requirement for stick pushers in T-tailed a/c.

The pushers were required in these a/c because the stall was unrecoverable.

Pushers are not required in a/c that can recover with standard pilot actions.

We are seeing high altitude stalls all the way to the ground and not just in Airbii - there's also at least one single engine turboprop I know of

To recover from a stall in an a/c certified as able to recover, you must first recognise it, then take appropriate corrective action.

Recognition becomes harder when the a/c settles into a steady state as with AF447 for which we do have data.

Certification requires the stall be recognisable. The nose drop has been superceded by aural warning, but as others have pointed out the human brain can shut down the auditory channel in high stress situations. I was in a simulator when the other pilot went inverted at 16,000' (white on black AH) and kept it there while I was shouting in his ear all the way to the ground.

What still bothers me about Brand A is that so far I have not heard of any test flights to determine stall behavior and recovery at any altitude.

Brand B seems to recover from high altitude stall events, but I have not come across any discussion that Brand B does stall test flights even though prevailing sentiment is that they likely do.

Would it, if the stab trim was wound fully back, the speed brought back to less than 100kts, with full power on and descending fast?