Minibus (A320) Stall Recovery

[TSIO540]

Hi folks,

I've searched the forums, but can't find discussion on my particular query.

For the A320, can anyone shed light on why:

if in clean configuration and below 20,000ft, select flap 1

is considered only AFTER:

flight path, recover smoothly

Surely selecting flap 1 after the fact is a bit moot..

[compressor stall]

It's not to get out of the one you were in, rather to stop you getting into it again.

[Fly3]

Flap 1 will reduce Vls considerably and hence aid the stall recovery. Could even make stall recovery unnecessary.

[vilas]

Fly3
stall is an angle of attack phenomenon so recovery is to be effected through pitch down and subsequent thrust increase. So flaps are to be used only after recovery as compressor said.

[stilton]

I thought the Bus was stallproof

[ok45]

Slats effect

Extension of slats will let you stall at a higher angle of attack. So IMHO it will help on the recovery as well as not getting into a secondary stall. Of course the primary method to get out of stall is to reduce the AoA. Hence it comes first..

[tom775257]

I suspect there is an aspect of almost muscle memory with this also.... you hear STALL STALL STALL you lower the nose. Then after that you can have a think about what comes next including your altitude, what was the flap altitude limit etc.. which will take a few more seconds to think about.

[EGPFlyer]

I thought the Bus was stallproof

Only in normal law. In alternate/direct law you can stall like any other aircraft

[CaptainProp]

Oh dear, here we go agan....

EGPFlyer, stilton was being sarcastic and I think he knows something very important, that you (?) and many others seem to have misunderstood - The airbus can stall, in any flight control law, in any configuration, at any altitude.

It's an aircraft. Aircraft have wings. Wings can stall. End of.

[subsonicsubic]

I fly baby planes. They only have trailing flaps - no leading edge droops.

But surely setting flap 1 in a 320 will immediately reduce the angle of attack.

Feel free to "attack" me if my supposition is incorrect.

[vilas]

Capt prop
"It's an aircraft. Aircraft have wings. Wings can stall. End of". Sorry it's not end of it at all

[CaptainProp]

Yes it is. At least as far as commercial aircraft like the Airbus, Boeing, Embraer etc goes.

The airbus control laws provide early warning and limited protection against high load factors, AOA, high speed etc etc.

The flight control laws do not make the aircraft immune to stall.

From the Airbus Flight Crew Training Manual:

Protections are intended to:

• Provide full authority to the PF to consistently achieve the best possible aircraft performance in extreme conditions
• Reduce the risks of overcontrolling, or overstressing the aircraft
• Provide PF with an instinctive and immediate procedure to ensure that the PF achieves the best possible result.

Not immune to stall.

Here, a fully serviceable airbus 319 stalled:

Chaotic CRM blamed for Chinese airbus a319 stall incident during approach

Whatever anyone tells you, it can stall in normal law, all it needs is to be misshandled or get a little "help" from a wind shear or downburst just as you reach a-max/a-floor.

[vilas]

Capt Prop
You are not contributing anything to the original question. I read the CAAC report. Since stall is AoA phenomenon, rapid changes due severe environment can do anything with any aircraft but aircraft response is not the same in Boeing and AB. In AB FBW aircraft computers act towards recovery. Stall recovery cannot be practiced in normal law by mishandling or any way.

[rudderrudderrat]

Hi TSIO540,

Surely selecting flap 1 after the fact is a bit moot..

Your first actions must be to get out of the stall "(no longer stall indications):" by reducing the AoA.

The other actions are listed to aid recovery to your original flight path and are done sequentially and without any significant delay.
If you received a stall warning at 2,000 ft (say whilst trying to intercept the ILS) then you must recover without contacting the ground. Selecting F1 will aid in minimum height loss whilst avoiding any "stall stall" caused by the +ve delta g you will need to pull (which is not felt in the sim) in order to change the trajectory.

"THRUST
SPEEDBRAKES
FLIGHT PATH RECOVER SMOOTHLY
• If in clean configuration and below 20 000 ft:
FLAP 1 SELECT
Note: If a risk of ground contact exists, once clearly out of stall (no longer stall indications), establish smoothly a positive climb gradient."

[TURIN]

I'm getting worried now.

Are there still pilots out there that think an Airbus cannot be stalled?
In any control law state?

Really?

After everything that has happened over the last few years?

[CaptainProp]

Vilas, the problem is that "qualified" and experienced airbus pilots are flying around thinking the aircraft is immune to stalls.

With regards to selecting Flap 1, and as already mentioned by previous posters, the FCOM only recommends selecting Flap 1 When out of stall.

From the FCTM:

STALL RECOVERY - The immediate key action is to reduce AOA: The reduction of AOA will enable the wing to regain lift. This must be achieved by applying a nose down pitch order on the sidestick. This pilot action ensures an immediate aircraft response and reduction of the AOA. In case of lack of pitch down authority, it may be necessary to reduce thrust.

Simultaneously, the flight crew must ensure that the wings are level in order to reduce the lift necessary for the flight, and as a consequence, the required AOA. As a general rule, minimizing the loss of altitude is secondary to the reduction of the AOA as the first priority is to regain lift. As AOA reduces below the AOAstall, lift and drag will return to their normal values.

- The secondary action is to increase energy:

When stall indications have stopped, the flight crew should increase thrust smoothly as needed and must ensure that the speed brakes are retracted. Immediate maximum thrust application upon stall recognition is not appropriate. Due to the engine spool up time, the aircraft speed increase that results from thrust increase, is slow and does not enable to reduce the AOA instantaneously. Furthermore, for under wing mounted engines, the thrust increase generates a pitch up that may prevent the required reduction of AOA. When stall indications have stopped, and when the aircraft has recovered sufficient energy, the flight crew can smoothly recover the initial flight path.

Here some comments on the subject from two very experienced guys, an interview with a Terry Lutz, airbus experimental test pilot and Boeing deputy chief 777 test pilot Van Chaney, last year in Flight Global:

.....pilots have been incorrectly trained for years to concentrate on maintaining height. "You must be willing to trade altitude,"

Pilots need to identify the risk of stall at high altitude, he says, recognise the onset of buffet and memorise appropriate pitch and power settings. But they must also know how to break the stall, with nose-down input, and - crucially - be patient. "Airspeed build slowly. Altitude must be traded for airspeed," he says, adding that engine thrust might be ineffective.

Chaney says thrust demands particular attention, particularly during low-altitude recovery. "I caution our pilots to be very careful with thrust application," he says. Restoring normal pitch and roll, he stresses, are "of secondary importance", particularly in a turning stall, for which he advises a two-step recovery - lowering the nose before smoothly rolling back to the horizon as airspeed increases. Simultaneous dual-axis recover is "not desired", he says, because it risks higher tail loads and reduces the effectiveness of control surfaces, delaying recovery.

"You fly into the stall, and fly out of the stall," he says, cautioning that rapid reduction of the angle of attack risks dropping the horizontal stabiliser into the wing vortices.

[stilton]

'Are there still pilots out there that think an Airbus cannot be stalled?
In any control law state? '



There were three on AF447.

[Genghis the Engineer]

Joint Boeing / Airbus view on the subject...

Royal Aeronautical Society | Aeronautical Journal | Stalling transport aircraft

I can read it where I am, although some IPs may not.

Just picking a useful paragraph from it...

Typical stall characteristics of transport aircraft in 1g non-accelerated flight (ref FAR Part 23.201) begin with the onset of initial buffet. This is best described as light airframe buffet which begins a few knots prior to stick shaker. As the aircraft approaches CLmax the level of buffet generally increases and can become severe to deterrent in nature. It is not uncommon to see buffet with a repetitive load factor of ±1g in the vertical direction and ±·5g in the lateral direction (see Fig. 20). It feels similar to driving an automobile across railroad ties. Buffet on large aircrafts tends to be much greater than experienced in smaller aircraft. This is due to wing airflow separation and turbulent airflow vortices which produce a strong excitation forcing function on the wing. This excites the fundamental frequency of the fuselage leading to large vertical and horizontal deflections. It can be very evident on the flight deck, where anything not securely tied down, such as an errant water bottle, can get hurtled into the air.

Stall identification is deterrent buffet for most recent models in the clean wing configuration. With flaps down, however, stall identification is either full column deflection to the control stop for two seconds, with no further pitch increase, or a nose down pitching moment that cannot be readily arrested.

Followed a bit later by..

Recovering from a stall is straight forward and is in fact nearly identical to that used in general aviation aircraft. First and foremost the angle-of-attack must be lowered using elevator. During recovery the buffet level can momentarily increase, however, this tends to be transitory in nature. Engine thrust can also aid in stall recovery but, the timing of its use is absolutely critical. If thrust is added too soon, the upward pitching moment of under wing-mounted engines may cause an increase in the angle-of-attack. Under certain conditions it may even be necessary to reduce thrust to prevent the angle-of-attack from increasing (Ref. 3). Regardless of when or if thrust is used, the altitude cannot be maintained and should be of secondary importance to reducing the angle-of-attack with the elevator (Ref. 2). Also, of secondary importance, is the restoration of normal pitch and roll attitudes. Flight testing has shown that a properly conducted stall recovery at low altitude using the elevator as the primary control typically results in minimal altitude loss.

[vilas]

Now there is Stilton who has no idea what is he talking about and yet would like to comment. In normal law this aeroplane has been designed to avoid stall in average circumstances and pilot cannot override them. But if it encounters environmental factors beyond those parameters surely it can. Yet those protections make the aeroplane safer than those without it, no mistake about it.

[Microburst2002]

Airbus "don't stall" in normal law because its FCS is designed not to allow that to happen. A different thing is that Airbus FCS is failure proof or perfect.

By the way: What happens if you fly at VLS at level flight, stick loose, with CONF 3, and then you select flaps zero? clac, clac. Ooops!! Seriously. What will happen? Will the FCS pitch the a/c down to get the AoA to alpha prot? Will it just switch to ALTN law, or abnormal attitude law. If still in normal law, Will you get the stall warning or will it be a "silent" stall?

Of course airbuses can physically stall.

The stall recovery procedure is very old. It used to be hidden in the SUPs, then things happened and it was promoted (embarrassingly) to the "front page", that is, the QRH.