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Old 16th May 2010, 13:04   #1 (permalink)
 
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New Airbus STALL RECOVERY procedure

No comments on the FOT Airbus issued this past week advising of a revised STALL RECOVERY procedure.?
FIREWALLing the throttles first has been the drill since primary training but now Airbus are saying to wait until the pitch has been lowered as it might even be necessary to reduce thrust to regain pitch authority. This seems to be quite a change to just throw out there with no forewarning or am I reading too much into it.

For the A320 fleet:

As soon as any stall indication (could be aural warning, buffet...) is recognized, apply the immediate actions :
- 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
- BANK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . WINGS LEVEL

• When out of stall (no longer stall indications) :
- THRUST . . . . . . . . . . . INCREASE SMOOTHLY AS NEEDED
Note: In case of one engine inoperative, progressively compensate the thrust asymmetry with rudder
- SPEEDBRAKES . . . . . . . . . . . . . . . . . . . CHECK RETRACTED
- FLIGHT PATH . . . . . . . . . . . . . . . . . . . RECOVER SMOOTHLY
• If in clean configuration and below 20 000 feet :
- 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.
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Old 16th May 2010, 13:41   #2 (permalink)
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The advice is fairly standard certification stall stuff - concerned with maintaining/recovering control rather than minimising height loss. Other than in situations near to terrain it makes real good sense. Many civil OEMs, and probably all military, will investigate other stall manoeuvres and recovery techniques to address other than simple certification situations.

Suggest you search some of John Farley's posts on stall recovery.

Two concerns with an immediate slam throttle input -

(a) the underslung engines will provide a significant nose up pitching moment as the RPM/thrust ramps up

(b) due to the high alpha, the change in airflow direction at the engine intake will provide a significant vertical force at the engine intake lip as the RPM/thrust ramps up, adding to the nose up pitching moment. This effect is seen to be critical most commonly in piston to turboprop conversions where the heavier piston engine is replaced by a lighter turboprop located further out to the front of the aircraft .. providing an increased pitching moment due both to increased engine power (usually) and the increased pitching arm from the CG.

A third possible concern involves gyroscopic precession as the nose pitches up which may provide some yaw .. which is not what we want at the stall ...

Perhaps Sean R's voice finally has been heeded by the OEMs ?
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Old 17th May 2010, 17:58   #3 (permalink)
 
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Not an AB pilot but wondering whether this is really a "revised" procedure or a "new" procedure inserted in recognition that even with its elaborate flight envelope protection an Airbus can stall.

The old "full throttles, etc..." thing applies to an "approach to stall/stick shaker" situation where stall has not yet developped and should still be valid.
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Old 17th May 2010, 19:46   #4 (permalink)
 
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in "normal law" you can not fly the Bus into a stall....
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Old 18th May 2010, 00:42   #5 (permalink)
 
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This FOT was prompted by several events in airbus aircraft (not only FBW) where high angle of attack situations were not handled optimally. At least one hull loss may well be attributed to this condition.

The previous stall recovery checklists did not have enough emphasis on the immediate requirement for a reduction in angle of attack.

The above comments regarding 'slam' TOGA thrust, particularly with respect to nose up pitch moments and the real possibility of a secondary 'g' induced alpha exceedance during the initial recovery process, also lend weight to the new procedure.

In FBW aircraft, where stall recovery would normally only be seen in an alternate law state (with reduced feedback protections at the sidestick) , this is even more relevant.
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Old 18th May 2010, 08:36   #6 (permalink)
 
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Hi ,

Where is this procedure writen?
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Old 18th May 2010, 08:52   #7 (permalink)
 
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i like this comment

in "normal law" you can not fly the Bus into a stall....


browsing thru FCTM regarding protections in normal law, we have high pitch protection, low energy protection, high AOA protection, Alpha Prot, makes me wonder if this FBW airbus do reach actual stall condition... but if u are in low speed, high pitch (approach phase) and flying into build ups, u can actually be in a stall situation if there's very strong updaft in a few seconds towards the front part of the aircraft. the current recovery actions are to reduce the pitch as to reduce the AOA, wings level, and simultaneously apply full power till u are out of stall and once the speed builds up, u can reduce the power, or re-engage the A/thrust if Alpha Prot became active previously, and return to your original path (miss approach if in approach phase). height loss will be minimal.
but if u are up there at 40'000 feet, in clean config, and suddenly u hit a severe CAT, i think it is more practical to unstall the surfaces, ie. to reduce the pitch and AOA, and wings level, before u apply power to increase the speed. height loss is not a primary concern in this situation. furthermore, at high altitude, a sudden increase in power demand might choke the engines, resulting in engine stall, plus unneccessarily firewalling the engines that added to the maintainance cost.
from my opinion, they should come out with stall recovery on approach/near terrain as well... separate the recovery procedures so that pilots will be clearer on the actions to be done in different situation.
my 2 cents....i might be wrong, and open for better explanation...
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Old 18th May 2010, 09:59   #8 (permalink)

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nnco

Quote:
FIREWALLing the throttles first has been the drill since primary training
I think the clue to answering your concerns is in your own words above. What is taught in primary training is naturally relevant to (and optimised for) the sort of aircraft used for primary training as well as the pilots experience at that stage.

I would see the advice you are concerned about as emphasising what experienced pilots should already appreciate when flying aircraft with a low thrust line and not as something new.
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Old 18th May 2010, 10:39   #9 (permalink)
 
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not quite agree with u there john... training should be of level standard regardless of your level of experience. thats why we have SOP..
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Old 18th May 2010, 16:19   #10 (permalink)

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syedo

I had always viewed SOPs as an aid to standardising pilot actions in respect of a particular type of aircraft across a range of pilots.

They may also be used by an employer to allow multi-crew operations to be standardised from entering the cockpit to leaving it so that two pilots who may never have flown together before feel completely at home.

The idea of writing an SOP (about any topic or phase of flight) that is optimum for a single piston trainer as well as for a large multi engined airliner strikes me as a little unusual.

JF
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Old 18th May 2010, 17:00   #11 (permalink)
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strobes on

" In FBW aircraft, where stall recovery would normally only be seen in an alternate law state (with reduced feedback protections at the sidestick) , this is even more relevant. "

This may be a fine point, but you equate "FBW" aircraft with Airbus "programming". Sequencing Thrust/Pitch is not necessarily applicable across other types, but is type specific, no?
 
Old 18th May 2010, 22:13   #12 (permalink)
 
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Quote:
in "normal law" you can not fly the Bus into a stall....
AFAIK the bus CAN be also flown into a stall in Abnormal Law (a flawed Normal) where the airplane enters an unusual attitude allowing pilots to "manually" get out of it. As a consequence of the plane sensing something gone wrong, the following changes happen in the law during the recovery:
- Pitch becomes Alternate (Load Factor protection, no Autotrim)
- Roll becomes Direct (mechanical yaw control)
- No reversion to Direct after LDG Gear extension
After recovery:
- Pitch stays Alternate without protections but with Autrotim
- Roll becomes Direct
- Yaw becomes Alternate

As you may suddenly get into Abnormal at any time, I've reason to believe the FOT is referred to this condition more than Alternate, Direct and MECH BCK, where the crew is well aware the plane can stall.
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Old 20th May 2010, 15:35   #13 (permalink)
 
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bear

Yes - I was referring only to Airbus FBW aircraft. Should have made that clearer.
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Old 20th May 2010, 17:13   #14 (permalink)
 
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A very good document from British CAA that has a lot in common with the new procedure:

Applicability: RETRE, TRIE, TRE, SFE, TRI, SFI
Effective: Immediate
STALL RECOVERY TECHNIQUE
1 Recent observations by CAA Training Inspectors have raised concerns that some instructors (both SFIs and TRIs) have been teaching inappropriate stall recovery techniques. It would appear that these instructors have been encouraging their trainees to maintain altitude during recovery from an approach to a stall. The technique that has been advised is to apply maximum power and allow the aircraft to accelerate out of this high alpha stall-warning regime. There is no mention of any requirement to reduce the angle of attack – indeed one trainee was briefed that “he may need to increase back pressure in order to maintain altitude”.
2 It could be argued that with all stall warning devices working correctly on an uncontaminated wing, such a recovery technique may well allow the aircraft to accelerate out of danger with no height loss at the lower to medium altitudes. The concern is that should a crew be faced with anything other than this idealised set of circumstances, they may apply this technique indiscriminately with potentially disastrous consequences.
3 The standard stall recovery technique should therefore always emphasise the requirement to reduce the angle of attack so as to ensure the prompt return of the wing to full controllability. The reduction in angle of attack (and consequential height loss) will be minimal when the approach to the stall is recognised early, and the correct recovery action is initiated without delay.
NOTE: Any manufacturer’s recommended stall recovery techniques must always be followed, and will take precedence over the technique described above should there be any conflicting advice.
4 Any queries as a result of this FCTN should be addressed to Head of Flight Crew Standards at the following e-mail address: flightcrewstandards@caa.co.uk.
Captain David McCorquodale
Head of Flight Crew Standards
21 April 2010
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Old 20th May 2010, 17:50   #15 (permalink)
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indeed one trainee was briefed that “he may need to increase back pressure in order to maintain altitude
- heaven help us! Where do they get these trainers from?
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Old 20th May 2010, 18:04   #16 (permalink)
 
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From day one of flying a plane were we not taught to lower the nose first to break the stall by restoring the airflow over the top of the wing?

The A320 is an aircraft after all, I know sometimes it is easy to forget!
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Old 21st May 2010, 03:45   #17 (permalink)
 
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The first order of business is to reduce the angle of attack. Nothing new there. No surprise. At high altitude that reduction of attack angle may be as much as negative 10 or 20 degrees and will result in a number of thousand feet loss of altitude.

Accounting for variables, you don't necessarily need to 'slam' any FADEC controlled engine through the instrument panel. FADEC will merely set power based on the detent at whatever rate IT determines.

Engine mounting and resulting thrust vector also plays a role and both Airbus and Boeing recognize this. With an ever increasing number of stall accidents and loss of control it has become apparent the industry needs a serious review of some basic aerodynamic facts and they have both amended their stall recovery procedure to emphasize this. You are well advised to continue the discussion and pay attention to your amendments and Authority safety notices about stall, approach to stall and recovery/recognition.

The 'notion' of many flight crew to misinterpret 'minimal loss of altitude' in stall recovery during a flight test has erroneously been interpreted by some to mean "within 100 feet". This notion needs to be erased.
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Old 21st May 2010, 10:28   #18 (permalink)
 
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Quote:
At high altitude that reduction of attack angle may be as much as negative 10 or 20 degrees
Do you mean "pitch attitude"? Don't think my passengers would enjoy negative alpha...
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Old 21st May 2010, 11:22   #19 (permalink)
 
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interesting

On the GLF we teach to keep pitch attitude, and just add FULL MAX WAR POWER, and the aircraft will power itself out of the stall.

My personal view is to easy the nose down to assist the MAX power to encourage air flow over the surfaces.

We do have the advantage of engines mounted above the wing, so the "push" is more down than up.


I have experienced a high altitude stall, due to getting very close, if not too close to the top of a CB, pitch down of 10 degress, was the only way to recover, as the power was already maxed out.


As to "my passengers would not like negative Alpa": Better then DEAD.
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Old 21st May 2010, 12:15   #20 (permalink)
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Quote:
Originally Posted by willie
At high altitude that reduction of attack angle may be as much as negative 10 or 20 degrees and will result in a number of thousand feet loss of altitude.
- no way Jose! Unless you have been indulging in some aeros or a major upset, a reduction of a few degrees is sufficient to silence the stick shaker or at worst to unstall the wing - to pitch 10-20 down from a normal high level stall AoA of around 5-7 degrees would be horrendous and would upset me as well as Tyro, spilling our 'retired' G&Ts in First and would undoubtably "result in a number of thousand feet loss of altitude" if not bits falling off the a/c

Anyone who has spent any time doing max performance manoeuvres will tell you that too much buffet in a max rate turn goes away IMMEDIATELY you relax the pitch a fraction. A little finesse is required and a wing that is unstalled is....well, a wing that is unstalled.. Certainly anyone getting 'used' to your 'high-level' technique will probably cause certain death in a low level eg approach stall.
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