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The vital importance of high altitude stall recovery training in simulators

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The vital importance of high altitude stall recovery training in simulators

Old 9th Oct 2014, 02:09
  #41 (permalink)  
 
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There is no aeroplane in this picture

Huh?? What is your point?
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Old 9th Oct 2014, 02:37
  #42 (permalink)  
 
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@ glendalegoon and clandestino

And in that case (since you are both agreeing) what is unfortunate is that a whole generation has been, in effect, misled into thinking that their "approach to stall" recovery was the technique whenever the word "stall" was involved.

For those interested, there's a major revision to FAR part 60 in the works (there's a NPRM out for comment right now) which SIGNIFICANTLY changes the fidelity of simulators in stalls AND significantly changes the instructional tools as well.
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Old 9th Oct 2014, 03:38
  #43 (permalink)  
 
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mad flt scientist

I was not misled as my hand dandy Aircraft Manual indicates that considerable altitude will be lost in a high altitude stall recovery.

Doing a simulator check and the combo apch to stall recovery/windshear recovery is one thing...but

PUSHING THE CONTROL WHEEL FORWARD in a complete high altitude stall is always in my mind (not that I have stalled or even approached a stall at high altitude)....

ask the pilots of AF447 about being misled in stall recovery!
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Old 9th Oct 2014, 05:00
  #44 (permalink)  
 
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Clandestino...

It is not and was never taught this way as it is impossible to power out of stall for any aeroplane except for aerobatic ones of extreme performance (e.g. Su-31 and -35).
It has definitely been taught to power out of a stall event and it is definitely possible to do so in a number of airplanes.

A stall event is any condition where you have a stall horn, low speed buffet, stick shaker, or stick pusher. It is now supposed to be taught that you are to treat all cases as being equal. Meaning that the "approach to stall" exercise that is taught in training is equal to an actual aerodynamic stall.

That, however, is not the case with a number of airlines - mine included.

As for powering out of the approach to stall exercise, I can do it in a SA227 and not only not loose any altitude, I will CLIMB less than 4 seconds later! I can power out of that and climb too. When the stall horn goes off I am at 1.1Vs and decelerating. I'm less than 10% away from the stall when I do this maneuver. This is exactly what confirms some instructors 'feeling' or 'thoughts' that this exercise should be taught that you should maintain altitude on recover - because it's possible... with an empty airplane, at 10,000' feet, while slowing down at a steady rate and when the crew is anticipating the stall horn and ready to slam full power... oh and no ice. How does that replicate any sort of situation that a crew would find themselves in where they're so close to the stall that the stall horn goes off?

The issue is that instructors teach the approach to stall exercise as a "precision flying maneuver" instead of an emergency maneuver. Ignorance is huge in this area.

I'd recommend reading this AC on the matter: https://www.tc.gc.ca/eng/civilaviati...-700-1793.html

That AC acknowledges that current practice places an emphasis on minimum loss of altitude verses positive recovery from a stall event.

A couple quotes from the AC:

"This AC is consistent with previous TCCA guidance material (CBAAC 0247), which focused on eliminating a procedure which focuses on "powering" out of a near-stalled condition with an emphasis on a minimum loss of altitude."

"...although a successful recovery may be possible at low altitudes, this "powering out" technique may be totally inadequate during manoevering flight or during flight with icing contamination or at high altitude, due to the lack of excess thrust."

This is the most important quote from what I've seen:

"The standards which require training for recovery from an approach to a stall with ground contact imminent should not be interpreted to mean that an aeroplane should be powered out of a high angle of attack condition and any altitude loss avoided even though close to the ground."

"Reducing AOA is the only effective recovery action from any high AOA condition, even though a loss of altitude will most likely occur. Although thrust may supplement the recovery, thrust is not a primary control. Reducing AOA at the first indication of stall is more effective in minimizing altitude loss than attempting to power out and subsequently encountering a stall or aeroplane upset."
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Old 9th Oct 2014, 06:18
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To be fair, it would seem that when these exercises were created the only thing that was of concern was a low altitude stall leading to impact with terrain. Little or no altitude loss was of prime concern in order to try & avoid impact. These exercises were done in the sim at 10,000' in order to take a little of the stress out & ensure that impact did not occur, as that was considered negative training. Perhaps they should have been done at lower altitudes in order to create a realistic scenario & instil some respect for the seriousness of the situation.

However, this has now lead to these techniques being applied by flight crews across the entire stalling scenario spectrum, including high altitude stalls & upsets. Due to the lack of specific training in high altitude stalls, some pilots have fallen back on the only stall recovery techniques that they know.

The large range of operating conditions that are experienced by a airline jet pilot today means that there is not a 'one size fits all' for many areas of the operation. There are also differences between flying smaller, prop driven aircraft & jet transport aircraft. Flight crews need to understand that & be comprehensively trained in ALL aspects of the operation, including the differences in stalling at low & high altitude. D.P. Davies book, Handling the Big Jets, is a good start for those moving onto jet transport aircraft however, a lot of those who I fly with have never read it.

We have already had a good example of what happens when you try to use techniques taught when learning to fly on large jet aircraft when AA587 lost it's tail due to the F/O's excessive use of rudder in turbulence. It appears that he was using rudder to 'pick up the dropped wing', which is a technique I was taught when learning to fly. This technique was taught in order to prevent a further wing drop at the stall due to aileron input. When I first started flying jet transport aircraft, I remember reading somewhere that 'except for an engine failure, or when in the circuit area, the rudder pedals should be used as footrests only'.

D.P. Davies gives the following advice to airline pilots. -

"Know your aeroplane - and I do not mean only your system drills. References have been made in this book to all sorts of qualities that the aeroplane may possess and you should know the values of them all for the type you are licensed to fly. All this information exists. Go and dig it out or have it dug out for you. Under normal operating conditions of course you can live without a lot of the more exotic information; but when things go badly wrong then having this background information might make all the difference.

Do not become lazy in your professional lives. The autopilot is a great comfort, so are the flight director and the approach coupler. But do not get into the position where you need these devices to complete the flight. Keep in practice in raw data ILS, particularly in crosswinds. Keep in practice in hand-flying the aeroplane at altitude and in making purely visual approaches.

Airline flying really is money for old rope most of the time; but when things get hairy THEN you earn your pay. The demand of jet transport flying can best be met by enthusiasm. Personal enthusiasm for the job is beyond value because it is a built-in productive force, and those who have it do not have to be pushed into practice and the search for knowledge. Enthusiasm thus generates its own protection. This is the frame of mind which needs to be developed for the best execution of the airline pilot's task."


Perhaps a little more personal enthusiasm for the job is all that is required.
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Old 9th Oct 2014, 12:32
  #46 (permalink)  
 
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Originally Posted by glendalegoon
then we have never practiced stall recovery in any us simulator session in any plane I have flown.
Neither did I... up to my last type rating. Courtesy of AF447, training programme on 738 sim now includes fully developed high altitude stall. Drill was to decelerate with idle thrust towards shaker but stop trimming short of it and to pull when it fires until getting the stall break with nose drop. Despite expecting what was to happen and immediately applying corrective action, usual altitude loss was about 10 000 ft. If anything, it served as useful reminder to watch my speed and never ignore shaker.

Originally Posted by Mad (Flt) Scientist
And in that case (since you are both agreeing) what is unfortunate is that a whole generation has been, in effect, misled into thinking that their "approach to stall" recovery was the technique whenever the word "stall" was involved.
Alas! One needs look no further than this thread to see how true it is. It might be that low quality of high school science education leaves today's pilot unprepared to appreciate difference in aerodynamics and performance brought upon flying in thin air. Anyway, this just cannot be made into a case of one-size-fits-all. Low altitude stall warning recovery and high altitude full stall require somewhat different techniques. Using the wrong one has good chance of terminating one's lifespan prematurely.

Originally Posted by Tee Emm
Huh?? What is your point?
That while I'm aware of instances of structural failures, powerplant failures and loss of control followed by diving into ground after entering thunderstorms, the only case of stalling in CB I can recall is Pulkovo 612 and entering the CB was only an accessory.
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Old 9th Oct 2014, 13:06
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These exercises were done in the sim at 10,000' in order to take a little of the stress out & ensure that impact did not occur, as that was considered negative training. Perhaps they should have been done at lower altitudes in order to create a realistic scenario & instil some respect for the seriousness of the situation.

Negative training - rubbish. The best low level stall recovery training is on short final at 800 feet on a coupled approach then close both thrust levers to simulate autothrottle system failure. That is basically what happened in the Turkish Airlines crash at Amsterdam. The airspeed rapidly bleeds off and the stab trim works overtime trimming back to hold the coupled glide slope. The stick shaker sounds about VREF minus 30 knots. It is best demonstrated first by a competent instructor, because things happen so quickly.
On go-around from VREF minus 30, thrust increase gives a strong pitch up already exacerbated by almost full back stab trim at the time the stick shaker operates. This is not a play fun exercise but deadly serious and it takes several attempts before recovery technique is refined. This is exactly what simulators are for.


But to conduct landing configuration stall recoveries at 5-10,000 ft in a simulator in order to avoid someone's idea of "negative training" is ridiculous.
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Old 9th Oct 2014, 15:13
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To be fair, it would seem that when these exercises were created the only thing that was of concern was a low altitude stall leading to impact with terrain. Little or no altitude loss was of prime concern in order to try & avoid impact.
The training requirement has been this way for a long time: 1) approach to stall with ground contact imminent, and 2) approach to stall with ground contact not imminent.

The only difference I see between the two is tighter margins when contact is imminent. When ground contact is imminent, you first need to ensure the aircraft is not stalled - usually by pitching down to reduce the angle of attack - then you need to establish a climb without delay. That last part is where you're performing with tighter margins (closer to the stall) because you're pulling out of the nose down attitude earlier; at a lower speed.

As far as it not being imminent, you're doing the exact same recovery except that you allow the airplane to pick up more speed before gently easing out of the nose low attitude.

But that's not how a lot of instructors see it.

They want you powering out of the stall event and they will argue that you are not stalled so you can power out and you can do it in the plane so how can you argue with that, right?

Well I strongly disagree. You can power out of a low speed scenario - 1.15VS or 1.2VS... but when you get any indication of a stall you MUST treat it as an actual stall. As I pointed out here, power must be applied after stall warnings have ceased. If it's just the warning and you haven't actually stalled, the warnings will cease almost immediately after you move the control column forward and you may apply power when the warnings do cease. However, if you are actually stalled, applying power before the airplane has recovered can easily put the plane into a severe upset, possibly a spin, due to the possibility of asymmetric thrust. A lot of transport and commuter category airplanes are sensitive when stalled - especially with swept wings. A little bit of yaw could be all that it takes to flip the airplane and put it into a spin.

However, this has now lead to these techniques being applied by flight crews across the entire stalling scenario spectrum, including high altitude stalls & upsets. Due to the lack of specific training in high altitude stalls, some pilots have fallen back on the only stall recovery techniques that they know.
This is perfect proof that you will revert to your training when in a bad situation. When you're trained to recovery from stalls when you're not actually stalled, when you are actually stalled you'll kill yourself if you did the same thing.

These approach to stall exercise were made decades ago. They were designed as approach to stalls instead of stalls because most airplanes didn't have a flight simulator that was easily accessible. Most companies were doing training in their aircraft. Understandably, most instructor pilots didn't want to be stalling a transport category airplane on a regular basis. Now that virtually every single commuter, transport, and business airplane has a simulator, there is no reason why they shouldn't be mandating actual stall training in the simulator.

This technique was taught in order to prevent a further wing drop at the stall due to aileron input.
This is a bit of a tangent but related to this statement.

Ever tried snapping aileron full deflection in a C172 at the point of stall? Which way will it go?

Theory says it'll go opposite the deflection (and it's correct) but in the Cessna it'll happily roll in the direction of the deflection.

It's good to teach and I recommend teaching it but it's virtually impossible to demonstrate to your student haha. "Hey Johnny, you don't wanna put aileron in at the stall because it'll roll the other way and might put you in a spin. Watch this!.... oh... it rolled in the direction of the deflection... hmm... well don't do it anyways!!!"

The reason for that is the outboard wing on the Cessna (due to washout) is generally not stalled when you stall the airplane. The whole point of washout is to provide roll control at speeds around stall speed. Not all airplanes have this which is why it's still a good practice to teach, regardless of being able to demonstrate it!

And as for picking up a wing... forget that! Pitch down and recover from the stall. There's a lot of simultaneous things happening during a stall recovery but pitching down is first, dealing with the wing drop is second.

D.P. Davies gives the following advice to airline pilots. -
That was an excellent excerpt! I fully agree... pilots do need more enthusiasm. Too many lazy pilots out there that don't take pride in doing their job well.
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Old 9th Oct 2014, 21:52
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The whole point of washout is to provide roll control at speeds around stall speed. Not all airplanes have this which is why it's still a good practice to teach, regardless of being able to demonstrate it!

Minor qualification - maintaining reasonable roll control is a Design Standard requirement and will apply to all conforming Types other than those of ancient design.

See, for instance, FAR 23.201(d).

If you play in the FAA website and have a look at superseded Regs .. you'll find this goes back a long ways ...
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Old 10th Oct 2014, 00:23
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Good point, John! Thanks for that reference.

That is talking about roll control up to the point of stall. I haven't seen a requirement for positive roll control after the point of stall. My reference to the C172 included flight after the point of stall. I tried many times and could not get the airplane to roll opposite the aileron input.

Due to the very forward CG limit and the Cessna wings being built to be quite stable, I'm not surprised. In a Cirrus with a CG towards the aft limit, I would not be surprised if you could get the airplane to roll opposite the aileron input after the stall.
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Old 10th Oct 2014, 04:39
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That is talking about roll control up to the point of stall

Yes, para (a) talks about that ....

Now, suggest you have another read of the words in the para cited ...
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Old 10th Oct 2014, 05:18
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IGh. Many thanks for all the very useful links. Really appreciated
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Old 10th Oct 2014, 08:36
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John,

I read paragraph (d). If the airplane doesn't roll more than 15 degrees, why would there be a need to move the ailerons from neutral?

If the airplane is consistently rolling left when stalled then a stall strip that is properly placed on the right wing will ensure the airplane stalls evenly and complies with paragraph (d) without any deflection of the ailerons from neutral. Or a stick pusher could be installed to ensure that the roll does not exceed 15 degrees.

I don't think paragraph (d) guarantees that you are able to use ailerons after the point of stall without the airplane rolling opposite to the aileron deflection.
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Old 10th Oct 2014, 12:17
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If the airplane doesn't roll more than 15 degrees, why would there be a need to move the ailerons from neutral?

Ah, but the devil is in the detail. The Reg indicates -

(d) During the entry into and the recovery from the maneuver, it must be possible to prevent more than 15 degrees of roll or yaw by the normal use of controls .. (my emphasis)

The inference is that (for some aircraft certifications, quite aggressive) normal control use may be required to prevent roll/yaw excursions.

For instance, one commuter category Type with which I am involved required very energetic control inputs for the certification compliance stalls to prevent excess roll divergence.

For other than ancient certifications, providing that the airframe complies with the TC (ie it hasn't been overly bent and twisted in use) control application must be normal in response. This is not to suggest that Captain Bloggs, line pilot, ought to be playing test pilot .. only that the typical worries about unexpected control responses are quarantined to older certifications (or unduly bent or twisted airframes ..)
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Old 10th Oct 2014, 12:50
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Imho it is not prudent to use aileron or rudder when in a stall (not stall aproach). There is no guaranteee how the jet will react to the input and there is no time to find out. Stall is a AOA problem and AOA is reduced by equaling pitch angle close to flightpath angle (the difference between both is AOA). The pitch must be changed, and bank up to 45° should have no negative influence for reducing AOA, it might even help to bring down the nose faster.

Take a look at the animation of AF447 event, link below.: From 02:11:33 until 02:12:15 the SS command was permanently full left, and the aircraft continued to bank right. At 02:11:56 FL 330 the pitch had dropped to -10°, AOA was 38°, 30° right bank, a good chance for recovery by forward stick and care about the bank later when AOA is reduced and the effectiveness of the ailerons is restored.




Reconstitution des 4 dernières minutes par les experts du 2ème rapport d'expertise
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Old 10th Oct 2014, 20:26
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John,

I think I found a more definitive source showing that you are correct.

The Part 23 Flight Test Guide says this under 23.201:

(3) Pilot Determinations. During the entry and recovery, the test pilot should determine the following:

(i) That the stick force curve remains positive up to the stall (that is, a pull force is required) (reference § 23.171) when the trim speed is higher than the stall speed.

(ii) That it is possible to produce and correct roll and yaw by unreversed use of the rolling and directional control.

(iii) The amount of roll or yaw encountered during the recovery.
RetiredF4,

I completely agree. The aileron control discussion was only to do with certification and I wasn't condoning usage of ailerons during a stall recovery - I teach to nose down first until pitch aligns with flight path, coordinated use of flight controls back to wings level, smoothly add power and ease out of dive.
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Old 11th Oct 2014, 11:27
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In all cases the ACs provide the expanded story of what the FAA thought its rules meant ie the recommended practices. In general, one follows the AC suggestions to minimise arguments and difficulties ..

To save others having to dig up the references ...

(a) heavy FTG is at AC 25-7C

(b) lighties FTG is at AC 23-8C

.. happy reading.
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Old 12th Oct 2014, 16:01
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For what it's worth, when I did my 737 TR in July, we practiced both "AF447" and "Turkish at Amsterdam" stall scenarios. In the case of the high-altitude stall, the recovery method we were taught, and that worked very well, was to get the nose well down, apply full thrust, and let the speed build to VREF40+100. We were also taught to use 230KIAS as a ballpark figure. Do NOT start pulling up until the tip of the speed vector touches 230, at which time you gently recover back to level flight. This method worked really well. We tried pulling up earlier, and most of the times this resulted in a series of secondary stalls and a massive altitude loss until you got down to thicker air. Nevertheless, we lost 7-10 000ft from FL400 before recovering, even with the correct procedure.
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Old 13th Oct 2014, 00:39
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Vref 40+100 is also a generic speed for minimum speed above FL250.
Below FL 250 the generic speed is Vref 40+80.


Given the gross weight changes the Vref 40+100 would be - 220 KIAS light and 250 KIAS heavy for above FL250.


Below FL250 the speed range would be closer to 200 KIAS light and 230 KIAS heavy.


None of these speeds are G adjusted - pulling G's changes the minimum speed.


Rules of thumb are good starting points but the reasoning and logic behind them is also part of the equation. 230 KIAS is a medium weight speed. Heavier would require more speed, and lighter less airspeed, if the technique agrees with Boeing's recommendations. Lower speed would require less G's, higher speed would allow more G's.
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Old 13th Oct 2014, 02:02
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We were also taught to use 230KIAS as a ballpark figure. Do NOT start pulling up until the tip of the speed vector touches 230, at which time you gently recover back to level flight. This method worked really well
While the above figures will get you out of immediate trouble, and depending on what weather conditions, if any, caused the high altitude stall problem in the first place, continue accelerating in the descent to severe turbulence speed before levelling out, will provide high/low speed margins in severe turbulent air.
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