Revised stall procedures

[Exadios]

This is what the big boys have decided to do in the future. This seems like a no brainer to me - why would you want to waste time playing with the engines when you are near, or in, a stall?

[Exadios]

So basically they are now using the recovery technique that we have been using in the light aircraft for a while now, reduce angle of attack, that is?

Specifically, reducing the the angle of attack by pushing the nose down.

 

 

[Guest ozzie]

Hells bells, makes you wonder don't it. Lower the freaking nose. Simple and only cure for that situation.

 

 

[Exadios]

Surely they wouldve been taught it in their basic training when they first learnt to fly... If all else was failing, they couldve atleast given it a shot.... I dunno...

My impression is that airline pilots do not do enough "real" flying and loose proficiency. I suspect they would benifited by an annual trip down to their local flying club or school and spending half an hour in the air with an instructor practicing stalls etc.

 

 

[facthunter]

This stuff relates totally to airliners operating at high altitudes. The margin above stall is only about 9 knots., depending on how close you are to "coffin corner". With airplanes that have underwing engines, ( the majority) applying extra thrust will cause a pitch up which may not be able to be controlled by the elevators, so the plane, if it isn't already, will become well and truly stalled. In this instance. It's not a question of proficiency at anything like normal stall recovery, but analysis and recognition of a situation that has only recently been assessed and understood. In search for efficiency, the limits are visited more and more. The air is very thin up there. At 18,000 feet half of the molecules of the atmosphere are below you. at about 40, 000 feet it would be around 80%.. You're talking of true airspeeds of 480 knots and a stall speed about 6% or less, below your cruise speed. You are in an environment where the plane could not do a 5 degree banked turn without getting a stall burble. You get a bit fast and you get high speed buffet. (Separation because of the airflow over part of the wing becoming supersonic). Nev

 

 

[Bandit12]

Fascinating info there Facthunter - makes perfect sense although I had never thought of the margin over stall as reducing that much due to altitude.

 

 

[Guest ozzie]

Hmm what you trying to say FH? I just read your post and then went back and reread the link. Yep it says what i thought "emphasis on reducing AoA". IE normal stall recovery. Their past training was trying to power their way out of the stall. now they are doing it the way we have always done . reduce AoA.

 

you talking about 'coffin corner'.? Even at that height just reducing AoA will get the aircraft under control again. Strikes me that if you are going to do anything with the power it will be to reduce it during the lowering to stop overspeed. Once control is gained reset power to cruise.

 

 

[Exadios]

This stuff relates totally to airliners operating at high altitudes. The margin above stall is only about 9 knots., depending on how close you are to "coffin corner". With airplanes that have underwing engines, ( the majority) applying extra thrust will cause a pitch up which may not be able to be controlled by the elevators, so the plane, if it isn't already, will become well and truly stalled. In this instance. It's not a question of proficiency at anything like normal stall recovery, but analysis and recognition of a situation that has only recently been assessed and understood. In search for efficiency, the limits are visited more and more. The air is very thin up there. At 18,000 feet half of the molecules of the atmosphere are below you. at about 40, 000 feet it would be around 80%.. You're talking of true airspeeds of 480 knots and a stall speed about 6% or less, below your cruise speed. You are in an environment where the plane could not do a 5 degree banked turn without getting a stall burble. You get a bit fast and you get high speed buffet. (Separation because of the airflow over part of the wing becoming supersonic). Nev

You have lost me. If you are only only 9 knots above stall why would you want to pull back on the stick or rev up the engines? And, with the lack of reliable air speed measurements and autopilot why would you want to climb to a higher altitude where the squeeze between Vne and stall speed becomes worse?

 

A stall is a stall at any altitude.

 

 

[Exadios]

For interest, here is what the BEA have released so far. Down near the bottom is:

 

"the inputs made by the PF were mainly nose-up".

 

 

[Yenn]

Talking to ex Airline pilots at Old Station, the quality of new airline pilots was discussed and the general concensus is that they are afraid to fly by hand, and leave it all to the autopilot. If the autopilot plays up they have little ability to look after the plane.

 

Reading the accident reports and news info confirms that opinion. For the moment stick with Qantas. [Moderated.]

 

What height do you have to be to run into the area with stall and overspeed very close together. I have been told that 42000' is perfectly manageable.

 

 

[Exadios]

Talking to ex Airline pilots at Old Station, the quality of new airline pilots was discussed and the general concensus is that they are afraid to fly by hand, and leave it all to the autopilot. If the autopilot plays up they have little ability to look after the plane.Reading the accident reports and news info confirms that opinion. For the moment stick with Qantas or an airline using "round eyes" as pilots.

What height do you have to be to run into the area with stall and overspeed very close together. I have been told that 42000' is perfectly manageable.

"Round eyes", such as French, for instance?

 

The squeeze between stall and Vne depends on wind loading and the Vne for a particular plane. For instance, gliders up to 100,000' have no problem. On the other hand the US U-2 aircraft has about 10 knots between the two at 75,000'.

 

 

[facthunter]

Exadios, I am not discussing Af447. Where did I say pull back on the stick? I said that adding power in an aircraft where the engines are underslung will cause a pitch up that may not be resisted by the elevators. There are new training techniques used by Boeing currently that have reviewed the use of power, of which there is generally not much extra available at height. The amount of height lost is considerable in doing the new procedures safely. Of course reducing the AoA is a critical factor, because it is what is causing the stall. You also get a reduction of induced drag immediately because you are momentarily reducing the requirement for lift, One negative of lowering the nose is that the thrustline does not have an upward component. Nev

 

 

[Exadios]

Exadios, I am not discussing Af447. Where did I say pull back on the stick? I said that adding power in an aircraft where the engines are underslung will cause a pitch up that may not be resisted by the elevators. There are new training techniques used by Boeing currently that have reviewed the use of power, of which there is generally not much extra available at height. The amount of height lost is considerable in doing the new procedures safely. Of course reducing the AoA is a critical factor, because it is what is causing the stall. You also get a reduction of induced drag immediately because you are momentarily reducing the requirement for lift, One negative of lowering the nose is that the thrustline does not have an upward component. Nev

Sure, but what you are saying just calls into question why would the stall recovery procedure be be anything else than to push the nose down since playing with the engines just makes a bad situation worse.

 

The thrust vector may help by reducing the wing loading but that's a (advsrse) square law relationship where as airspeed is a linear realtionship.

 

 

[Powerin]

So that means airliners at cruise altitude are operating at a very high angle of attack?

 

 

[facthunter]

All aircraft have a higher angle of attack as they approach their service or absolute ceiling. At the absolute ceiling if you slow up you stall and lose height, if you speed up you lose height, but don't stall. A stall is always an angle of attack.

 

Powerin, at the highest possible cruise height (which would not be safe in turbulence, or for manoeuvering) and sensible pilots keep away from, the airliner IS flying at a high angle of attack.

 

Exadios , it's a balancing act. Adding power can cause a pitch up which is just what you don't want, but the more power you have on the less height you will ultimately lose to effect a safe recovery, because all things being equal and making sure that good control is maintained, the less nose down pitch required and the lower the maximum rate of descent achieved. Once you establish a steep nose down attitude and high ROD the more chance of structural failure due overspeed or entering another dynamic stall if level off is too rapid Nev

 

 

[Exadios]

All aircraft have a higher angle of attack as they approach their service or absolute ceiling. At the absolute ceiling if you slow up you stall and lose height, if you speed up you lose height, but don't stall. A stall is always an angle of attack.Powerin, at the highest possible cruise height (which would not be safe in turbulence, or for manoeuvering) and sensible pilots keep away from, the airliner IS flying at a high angle of attack.

Exadios , it's a balancing act. Adding power can cause a pitch up which is just what you don't want, but the more power you have on the less height you will ultimately lose to effect a safe recovery, because all things being equal and making sure that good control is maintained, the less nose down pitch required and the lower the maximum rate of descent achieved. Once you establish a steep nose down attitude and high ROD the more chance of structural failure due overspeed or entering another dynamic stall if level off is too rapid Nev

I see your point but, at the altitudes where the two speeds come together, who cares about minimizing altitude loss?

 

Assuming that the plane has not been flown to the altitude where the two velocities intersect (and I certainly hope that would not happen) there is a nose attitude, not too much different to the attitude at which incipient stall occurs, at which the plane will fly. My point is that it is not necessary to go into a dive in order to recover from an incipient stall.

 

 

[facthunter]

At those altitudes and encountering circumstances of speed reduction, turbulence, and what you describe in your last para. where you would have more drag and hence a situation where you are losing speed, you MUST lose height as you may get into more trouble applying power, (nose up pitch) and you do not have enough energy to accelerate the plane without using height loss. The amount has been found to be much more than has been thought when this situation was assessed in the past, (easily up to 6,000 + feet, to safely recover .Nev.

 

 

[Exadios]

At those altitudes and encountering circumstances of speed reduction, turbulence, and what you describe in your last para. where you would have more drag and hence a situation where you are losing speed, you MUST lose height as you may get into more trouble applying power, (nose up pitch) and you do not have enough energy to accelerate the plane without using height loss. The amount has been found to be much more than has been thought when this situation was assessed in the past, (easily up to 6,000 + feet, to safely recover .Nev.

So the plane drops from FL350 to FL290. No problem. Still seems to me that the correct proceedure is to move the stick foward and then play with the power - as the change recognizes.

 

 

[facthunter]

Except that is the minimum if you do it right and there could easily be traffic under you. It pays to use the power but the technique has to be right with underslung engines. The older technique was just to add power, but the situation has been the subject of intensive analysis, which I think is good. Nev

 

 

[Exadios]

Except that is the minimum if you do it right and there could easily be traffic under you. It pays to use the power but the technique has to be right with underslung engines. The older technique was just to add power, but the situation has been the subject of intensive analysis, which I think is good. Nev

I imagine that these are profesional pilots so they are not going to do it incorrectly. Actually, I find your assertion regarding the 6000' a little hard to believe. These planes are not that bad at flying.

 

The problem with using the engines is mainly to do with the fact that they take a long time to respond and do not have much top end. When using the stick to increase speed there is one lag - proportional to the mass. Using the engines adds another lag. This logic applies to small planes as well (although the engines are more responsive).

 

In any case the decission has been made to use the stick first so the authorities cannot be too concerned about height loss.

 

 

[facthunter]

Jet engines ONLY take a long time to respond when they are doing it from idle. At high power settings it is almost instantaneous. The underwing placement of the engines is the issue, requiring the technique and care.

 

Whether you find my assertion hard to believe is not the point. It is straight from the current (latest) Boeing training and checking procedures. It's an energy available and increasing drag thing, not inertia only. Nev.

 

 

[djpacro]

I imagine that these are profesional pilots so they are not going to do it incorrectly.

That was indeed the problem. This article helps to explain the background to the "new" procedure.This is the new briefing by Airbus.

 

 

[Exadios]

Report reveals cockpit chaos in Air France crash.

[kaz3g]

All this talk about stalling heavy metal is interesting but not very relevant to what we do.

 

I recall completing my PPL in a brand new Warrior II after a background in gliding including a lot of time in motor gliders. The very experienced instructor had only very recently relinquished his grip on the school's Airtourer.

 

On my first lesson with him, Pat filled the tanks to the tabs only and away we went. Climbed to about 4000' near Benalla and we did a few stall recoveries. He didn't like my efforts which comprised lowering the nose promptly to restore flying speed before recovering from the dive. So Pat took over the controls.

 

He picked up a bit of speed downhill then stood it on its tail and chopped the throttle just before the stall calling: "Your aircraft!"

 

I kicked the rudder hard over, did a pretty fair stall turn and recovered from the dive.

 

WRONG!

 

Pat asked me how much height had been lost and I answered truthfully that I wasn't sure but probably around 300-400'.

 

He then demonstrated a powered recovery from the same extreme stalled position. Simply apply power and fly away with virtually no height loss at all.

 

He said survival was all about using all of the tools at your disposal. A functioning engine is a very effective tool when used correctly.

 

kaz

 

 

[facthunter]

Been recommending that for years. The way stalls are generally taught, is all wrong. You don't sse the one coming that gets you. Most of the real situation occurrences are while turning, often near the ground.(below 1,000 ft) and if you don't use the right technique you will be below the ground before you would recover. Most students, (and not just students) are scared of slow speed flight and doing stalls. A healthy respect is ok, but if you know exactly what you are doing then you shouldn't fear it. Nev