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-   -   New (2010) Stall Recovery's @ high altitudes (https://www.pprune.org/tech-log/417975-new-2010-stall-recoverys-high-altitudes.html)

s_bakmeijer 12th Jun 2010 13:33

New (2010) Stall Recovery's @ high altitudes
 
Any of you have received the new techniques/suggestions of high altitude (>25000') stall recovery training?

which trains to accept altitude loss by discon. AP/ATS and push nose down + advance throttles. But primary push nose down( to horizon).

--------
I just had my sim check-ride with this training,
Seems very effective, but contradict my core training and so my feelings.

you opinion please ! :ok:

protectthehornet 12th Jun 2010 13:44

high altitude stall recovery in the 4 transport jets I have flown (many certified in the 60's) have always called for loss of altitude in stall recovery or at least indicated that great altitude loss should be expected.

It sounds like you were misinformed prior to this.

and I will add that low altitude stall recovery (powering out) is only valid in a plane that is approaching a stall but NOT YET STALLED>

extending leading edge devices can also be part of the recovery

kenparry 12th Jun 2010 14:41

I agree the above. At high altitude, there is not enough thrust to recover using power alone.

Extract from the B767 FCTM (paraphrased a little):

If ground contact not a factor:
Apply max thrust
Smoothly decrease pitch attitude to approx 5 deg nose up
Level wings
Accelerate to maneuvering speed for flap position
Stop descent, return to target altitude
At altitudes above 20,000 ft lower pitch attitudes may be required to provide acceptable acceleration


The page I am looking at is dated 1 Jan 1996, so hardly new.

BOAC 12th Jun 2010 15:03


but contradict my core training
- maybe that was incorrectly taught or you mis-understood it. The aim is always to unstall the wings (assuming they are 'stalled' and not just the stick shaker) and achieve the minimum possible loss of height. That means that at 35,000' ft you can afford to lower the nose a bit (NB not a vertical dive!) and accept a few 100's or 1000's of feet loss but at 100ft try to avoid losing more than 100ft.

Centaurus 12th Jun 2010 15:32

In the simulator we practice stall recovery at stick shaker at 37,000 ft. The technique is to lower the nose to zero body angle while advancing the thrust levers to GA thrust. The aircraft will attempt to pitch up as speed is increased but it is important to prevent this natural pitch up tendency by maintaining zero degrees attitude until the airspeed has reached VREF 40 plus 100 knots. Typically at training weights in the 737-300 that is 230 knots.

Once that speed is attained, the aircraft is carefully levelled out. Usually 3000 feet is lost during this manoeuvre to reach 230 knots but that is the price of doing business. The VREF 40 plus 100 knots is the FCTM recommended speed for holding above 25,000 ft if speed is not available from the FMC and is also provides adequate buffet margin. The danger is where pilots try to recover with minimum loss of height and any premature recovery to attempted level flight often causes causes G buffet and more height loss. It is advisable to count on at least 3000 ft of height loss at these high altitudes.

s_bakmeijer 12th Jun 2010 16:09

exactly, i am practically new in high speed high altitude (jet) so, I was referring more at prop ops. where there are limits of about 150' of alt loss. but i think it was great this training.
and the approach to stall wasnt what i meant though,..
the part i meant was where you were past stick shaker and didnt correct accordingly... point where stick pusher kicked in.
it was a situation where an md80 crashed in south america where icing caused reduce engine power and these guys didnt act on anything letting the plane to stall completely where power was never applied.
something like that, im trying to find further info on it. if you have some, please inform.

what i had learned initially on jet is to discon.ap/ats accept alt loss where performance is limited, and lower nose + use lift improvement devices etc.

but now its initially nose-horizon, let that baby drop just to recover lift on wings..
good stuff !!!

PBL 12th Jun 2010 17:05


Originally Posted by s bakmeijer
what i had learned initially on jet is to discon.ap/ats accept alt loss where performance is limited, and lower nose + use lift improvement devices etc.

but now its initially nose-horizon, let that baby drop just to recover lift on wings.

I don't think that is quite what is going on. I take it you are speaking of an unaccelerated stall, at Vs1g. C_L increases right up to the stall break, but after a certain AoA it is likely that it increases only slowly (I don't know which specific airplane you are talking about, since you haven't said).

If you actually got the sim to Vs1g at altitude, you cannot necessarily expect it veridically to reproduce the behavior of the actual airplane.

PBL

BOAC 12th Jun 2010 17:37

NOT a good idea to go fiddling with flaps! :eek:. Ignore that one.

Boeing specifically prohibit it on the 737.

mad_jock 12th Jun 2010 18:52

These idea's about stall recovery in FAA turboprop pilots is quite common in my limited experence.

They will try and power out of it.

We had a flight upset on approach due to vortex wake from a 757 at Vmo and the rection of the FAA trained FO was to try and use full rudder to lift the wing. Thankfully the yaw damper was in so after the grunts and bulging thigh were spotted, I got it off him before he bent the airframe. But he was upset that I used Ailerons to correct roll.

On discussing other bits of his training it transpired this power out of clean stall with firewall power is the way they teach it. On questioning about if the procedure was the same for single engine work, it apparently was. The concept of Vmca apparently only apply's for engine failures on takeoff.

This was from an Emery Riddle grad who is quite a good operator on normal sectors. And he has apparently done advance flight upset sim courses in the sims in DC. But when you start digging deeper into some of the emergency handling stuff it is a bit different to what we get taught in the UK.

So if your a JAR pilot its well worth discussing these things if you head out of europe to lands of license converstions.

Willie Everlearn 13th Jun 2010 00:45

I'd just like to add the following.

All simulator data packages contain NO valid data beyond the "g" break. It was never required by Regulation or Certification. Beyond that point, the simulation software has no idea what to generate. So, once you pass the "g" break your experiencing the unknown and best advised to disregard what you get.
Your aeroplane will most likely behave quite differently.

Stalling a T-tail beyond the pusher into a fully developed stall will most likely be catastrophic in the actual aeroplane.

Willie :ok:

Pugilistic Animus 13th Jun 2010 01:10

Stalls always have the same exact cause, too much alpha and the main reason behind the thrust increase is to flatten the flight path and guard against height loss....but increasing the thrust also decreases the alpha by reducing the vertical component of thrust

guiones 13th Jun 2010 05:05

Stall vs Approach to Stall
 
Do not mistake the procedure with approach to stall, this "new" procedure is a remainder of the stall recovery, no matter how much one would like to not loose altitude, when in a stall, there is no choice; AOA must be reduced, the wings must have enough air flow and power alone will not do it; not on any commercial a/c no matter the weight or altitude.
There is an FOT from Airbus out after extensive Flight and Sim Tests, there will be procedures along the same lines from Boeing and the other mayor manufacturers.

Approach to stall recovery techniques are irrelevant actual stall recovery.


G

PBL 13th Jun 2010 11:29

Yes, let's indeed not confuse stall with approach to stall. Here is an example of such confusion:

Originally Posted by s bakmeijer
and the approach to stall wasnt what i meant though,..
the part i meant was where you were past stick shaker and didnt correct accordingly... point where stick pusher kicked in.

If you have a stick pusher on your airplane, then you are doing approach-to-stall recovery, because the pusher is there to stop you stalling the airplane, either because somebody didn't like what they saw in the wind tunnel, or somebody else decided there wasn't enough data about it.


Originally Posted by guiones
Do not mistake the procedure with approach to stall, this "new" procedure is a remainder of the stall recovery, .....
There is an FOT from Airbus out after extensive Flight and Sim Tests

You think people have been going out doing stalls in Airbuses to see what happens?

The aerodynamic characteristics of a modern commercial jet are determined in wind tunnels, mostly for certification purposes. The wind tunnel work determines how the wing behaves, not the whole airplane. It determines at what point lift drops off sharply, and so forth. There is a lot of data, but there is by no means everything. The point of "stall" is not necessarily defined as being where the lift drops off sharply; it is more often defined by a degree of buffet (I refer to the regs).

"Sim tests" cannot help anyone with stalls. Simulators are only veridical at most up to the point of defined-stall (which may be at lower AoA than lift-break). So anything you can do in a sim is an approach-to-stall procedure.

As far as I know, this is a result of the recommendations following the Colgan Air crash, during which the PF reacted inappropriately at approach-to-stall, at stick pusher.

PBL

Tankengine 13th Jun 2010 12:58

I hate to state facts here!:E
but
There is a new procedure from Airbus for the 330 [newly arrived at my airline anyway]

It basically states to lower the nose [with a note that this may need a reduction in thrust] then start to smoothly increase thrust while accelerating and to go flaps1 [LE devices] if below 20000' [sorry BOAC:ouch:]

Underslung engines may create more pitch up at low speeds/high AOA than elevator can pitch down!:eek:

Centaurus 13th Jun 2010 13:05


and the reaction of the FAA trained FO was to try and use full rudder to lift the wing.
FAA trained or not, it is a fact that using rudder to lift a wing is commonly taught in flying schools in Australia. Judging also by the questions that appear in the Pprune Instructor Forum, it happens elsewhere as well. It seems to be handed down from generation to generation of young flying instructors who in turn once they achieve Grade One instructor status teach new instructors.

It has proved impossible to completely eradicate this technique throughout many general aviation flying schools. But you would think when type rating courses are conducted this erroneous teaching would soon be discovered and rectified.

FullWings 13th Jun 2010 13:17

I think guiones has it right. Reality is just being restated. As you fly higher, the reduction in max. thrust available means that the speed at which you "fall behind the drag curve" increases, possibly to well above the stalling speed. At that point you have no choice but to descend (the aeroplane will do it for you), either by maintaining the same IAS and waiting for the thrust to come back :ooh: or by reducing pitch (and drag) and trading some potential energy for kinetic (height vs. speed) to get back earlier to a thrust>drag regime.

At progressively higher altitudes, stall recovery moves steadily towards the technique you would use in an unpowered aircraft, compared with lower down where minimum height loss is more important. The training doing the rounds at the moment may be because previous exercises concentrated more on low altitude mishaps?

guiones 13th Jun 2010 14:40

PBL, that is exactly what I am saying.

Airbus EV (Flight Test) did extensive stall behavior test on actual aircraft and then it compared it to the Sim behavior before they published the FOT.

G

guiones 13th Jun 2010 14:42

Tankengine, that is the FOT I mentioned in my posts.

The reduction in power is "you may" if you need it to regain or maintain pitch control.

G

Mansfield 13th Jun 2010 14:54

AC 25-7, Flight Test Guide For Certification of Transport Category Airplanes, Chapter 8, Para 228(b) states the following:
Some airplanes require artificial stall warning systems, such as stick shakers, to compensate for a lack of clearly identifiable natural stall warning to show compliance with the stall warning requirements of § 25.207. Similarly, some airplanes require a stall identification device or system (e.g., stick pusher, automatic inboard slat segment retraction, auto-trim, etc.) to compensate for an inability to meet the stalling definitions of § 25.201 or the stall characteristics requirements of § 25.203.
The stick pusher does not function as a stall warning device; that is the purpose of the stick shaker. The pusher is a stall identification device. It represents exactly the same thing as CLmax, and is used when CLmax either cannot be clearly identified or when the stall characteristics around CLmax are particularly unsatisfactory.

With respect to stall testing, the manufacturer does indeed conduct stall testing in flight, including at altitude. I have appended additional excerpts from AC 25-7A below. This language may give a better understanding of the issue from the authorities point of view.

I suspect that any new material on this topic from the manufacturers is a result of a rather extensive effort being put forth in the industry to understand loss of control accidents. I believe it would be a mistake to assume that it originates solely with the Buffalo accident.

AC 25-7A, Chapter 2, Section 6 – Stalls.

b. Explanation.
(1) The purpose of stall testing is threefold:
(i) To define the minimum inflight airspeeds and how they vary with weight, altitude, and airplane configuration (stall speeds).

(ii) To demonstrate that handling qualities are adequate to allow a safe recovery from the highest angle of attack attainable in normal flight (stall characteristics).

(iii) To determine that there is adequate pre-stall warning (either aerodynamic or artificial) to allow the pilot time to recover from any probable high angle of attack condition without inadvertently stalling the airplane.
(2) During this testing, the angle of attack should be increased at least to the point where the following two conditions are satisfied:
(i) Attainment of an angle of attack measurably greater than that for maximum lift, except when the stall is defined by a stall identification device (e.g., stick pusher).

(ii) Clear indication to the pilot through the inherent flight characteristics or stall identification device (e.g., stick pusher) that the airplane is stalled.
(3) The airplane is considered to be fully stalled when any one or a combination of the characteristics listed below occurs to give the pilot a clear and distinctive indication that he should stop any further increase in angle of attack, at which time recovery should be initiated using normal techniques. The stall speed is defined as the minimum speed reached during the maneuver, except for those airplanes that require stall identification devices (see paragraph 29b(3)(iv), below).
(i) The pitch control reaches the aft stop and is held full aft for two seconds, or until the pitch attitude stops increasing, whichever occurs later. In the case of turning flight stalls, recovery may be initiated once the pitch control reaches the aft stop when accompanied by a rolling motion that is not immediately controllable (provided the rolling motion complies with § 25.203(c)).

(ii) An uncommanded, distinctive and easily recognizable nose down pitch that cannot be readily arrested. This nose down pitch may be accompanied by a rolling motion that is not immediately controllable, provided that the rolling motion complies with § 25.203(b) or (c), as appropriate.

(iii) The airplane demonstrates an unmistakable, inherent aerodynamic warning of a magnitude and severity that is a strong and effective deterrent to further speed reduction. This deterrent level of aerodynamic warning (i.e., buffet) must be of a much greater magnitude than the initial buffet ordinarily associated with stall warning. An example is a large transport airplane that exhibits “deterrent buffet” with flaps up and is characterized
by an intensity that inhibits reading cockpit instruments and would require a strong determined effort by the pilot to increase the angle of attack any further.

(iv) The activation point of a stall identification device that is a strong and effective deterrent to further speed reduction. Paragraph 228 of this AC presents guidance material for demonstrating compliance of stall identification systems with the regulatory requirements of Part 25 of the FAR.

BOAC 13th Jun 2010 15:02


and to go flaps1 [LE devices] if below 20000' [sorry BOAChttp://images.ibsrv.net/ibsrv/res/sr...ies/shiner.gif]
- no apologies needed my reply was to a post about high-level stalls where deploying LE devices will probably put you on your back.

Centaurus - let's not confuse folk here please! The use of rudder to lift a stalled wing is ESSENTIAL and correct and MUST be taught. Use of aileron on a fully stalled wing will merely increase the wing drop (basic aerodynamics?) and will probably cause a spin.

Above the stall (ie stick shake) it is fine to use aileron.


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