New Airbus STALL RECOVERY procedure

[nnc0]

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.

[john_tullamarine]

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 ?

[DJ77]

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.

[Airbus_a321]

in "normal law" you can not fly the Bus into a stall....:8

[strobes_on]

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.

[A-3TWENTY]

Hi ,

Where is this procedure writen?

[syedo]

in "normal law" you can not fly the Bus into a stall....http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/nerd.gif


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...;)

[John Farley]

nnco

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.

[syedo]

not quite agree with u there john... training should be of level standard regardless of your level of experience. thats why we have SOP..;)

[John Farley]

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

[bearfoil]

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?

[fredgrav]

in "normal law" you can not fly the Bus into a stall....http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/nerd.gif

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.

[strobes_on]

bear

Yes - I was referring only to Airbus FBW aircraft. Should have made that clearer.

[guiones]

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: [email protected].
Captain David McCorquodale
Head of Flight Crew Standards
21 April 2010

[BOAC]

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?

[ItsAjob]

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!

[Willie Everlearn]

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.

[TyroPicard]

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...

[Gulfstreamaviator]

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.

[BOAC]

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.

[Capn Bloggs]

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”.

The "canned" stall recoveries in my Alteon course were basically run along the same lines - minimise height loss. That, of course, is not what you do, as you guys have pointed out, if you're already at full power, stalled and going nowhere.

[Admiral346]

Obviously if close to the ground, reducing height loss would be of up most importance during the recovery. A stall at altitude would allow a generous degree of nose down pitch and height loss during the recovery, something not acceptable on final approach.

A stall close to the ground would require a great deal of finesse to recover from. Max power and very carefully balancing a safe reduction in pitch against height loss while the wing unstalls and the aircraft powers out of it would seem to be in order.

Pancaking onto the ground in a flat, low speed condition would probably offer a greater chance of survival than stalling and crashing nose down or dropping a wing and spinning in.

Remember D.P Davies stating that "If ever the day should come when you are faced with the choice of stalling, or doing something else, choose the alternative."

[p51guy]

Wind shear training which happens close to the ground emphasizes not lowering the nose after full power application below stickshaker until recovery is complete. A stall could be caused by windshear close to the ground so tell me how Airbus now handles this. Lower the nose and smoothly add power???? Oh, that's right, an airbus cannot stall in normal law but can it hit the ground?

[john_tullamarine]

Wind shear training which happens close to the ground emphasizes not lowering the nose after full power application below stickshaker until recovery is complete.

The philosophy is that, given you have a high chance of dying if you don't do something drastic ... one is best advised to go with the procedure most likely to maximise survival chances in the short term ... if something else happens simultaneously .. perhaps it just wasn't your day ?

[Mad (Flt) Scientist]

Given that the best L/D likely occurs at or below shaker activation, if you are both in windshear and stalled, you need to lower the nose, both to (a) unstall the wind and regain control of your flightpath and (b) get to the airspeed/attitude/AOA where you have the best chance of your aircraft's performance being adequate to get out of the shear.

Sitting there with a stalled wing isn't going to do squat for your chances of climbing away from the ground. This is the fundamental flaw with the way the ridiculous "minimize altitude loss" is being indoctrinated into people via the PTS; once the wing is stalled, you are going DOWN. If you wish to stop going down, you have to unstall. Therefore lowering the nose to unstall the wing will minimize the altitude loss.

Unfortunately, the manoeuvre is invariably taught with a fully attached, pre-stall, wing, which gives the wrong lesson for the stalled case.

[galaxy flyer]

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.

That must be pitch and even then that is a lot--5-10 degrees nose down would be like it. Due to being power-limited, the only means to increase EAS and Mach is gravity.

[p51guy]

Sometimes in turbulence it may not be easy to determine if wind shear or just a basic stall do to inattention caused the stick shaker to activate breaking out at 500 ft. I totally agree with altitude to spare lowering the nose as you increase power is the best procedure. I know Airbus has had problems with max power with a pitchup. Never found it a big problem with Boeings using normal control inputs.

[p51guy]

Best L/D is well above stall speed. 1.3 minimum of stall speed rings a bell. Max lift occures right before stall but the drag is at max. That is why low altitude stall recoveries sometimes have to sacrifice speed for more lift to not impact the ground. Best L/D is close to best glide speed. It is best to not venture below this speed but some situations require it. The shaker is a warning you are approaching stall angle of attack but if you don't force it to go deeper into the stall you have almost max lift but also almost max drag. Breaking out at 500 ft getting a stick shaker and lowering the nose first would only compound your situation. High sink rate and low speed is not good. Add power to recover and minimize sink rate.

It has worked well for 107 years.

[ProfessionalAviator]

We must remember that in any aircraft, and Airbus is no exception, the greatest tool for safety is situational awareness. Let's hope that no computer program will ever replace the aviator in the flight deck.

In the case of a stall, an aviator must remember not just what was taught in the simulator but rather must imagine the conditions that were meant to be simulated.

I know we fly how we train, but the more experience teaches us, the more we should use it. A stall recovery procedure in the simulator is designed to test the pilot's mastery of the aircraft, in the hopes that that knowledge will be used later to fly the aircraft safely in all kinds of unforecast conditions.

I remember, as I was teaching in the simulator in a previous position, the students were quite critical of the complexity of a specific procedure.

My point to them was that the procedure was not designed to fail them, but rather provide good pointers as to how the aircraft may behave in rapidly changing conditions and airspeeds. Invariably, once the students progressed through the training, they came to appreciate the value of that maneuver.

In the case of an actual stall (such as Air France 447 may have entered- since we don't know everything just yet), conditions change so quickly that pilots have to step out of their "as trained" comfort zone, and process these changes and react, perhaps differently, but with knowledge and mastery.

I hate to reach out to old addages, but good old stick and rudder skills are invaluable in such situations, since Airbus or not, modern aircraft still employ those devices.

Pilots should keep in mind all this, as they graduate a training program. Once entrusted with the lives of people, I must repeat a statement I made to one of my students in the past: One must put the thinking hat on and keep it on until safely at the gate.

[Microburst2002]

MAD SCIENTIST

in the case of the windshear and depending on circumstances it can be better to be at the verge of stall than to pitch down. A quasistalled airplane goes down, but a quasistalled airplane pitching down goes down faster, and you need height to recover the speed you need to make a pull out. You might get in a secondary stall or simply crash before you have enough energy. In these cases, it can be better not to sell any potential energy and hope that the windshear will end soon.

Windshear is a problem of time, after all.
____________

As far as I know, Airbus drivers do not practice stalls in the sim.

Because airbus FBWs are supposed not to stall.

but they do

Until one year or so, stall recovery technique was only included deep in some FCOM (you never know which one, exactly). They decided to include it in the QRH as a proper procedure and now we have one more memory procedure... (20 years late!).

Before coming to the airbus, I saw too many FIs giving too much importance to the height loss during a stall recovery. I always thought that the wings are what matters, and the sooner you unstall them, the better, because the less energy will be lost.

[Jane-DoH]

Not to sound sciolistical or anything, but considering how much of commercial aviation is based on proceedure

I think the procedure should emphasize the fact that below a certain altitude, the traditional stall recovery procedure of firewalling the throttles should be used.

[PantLoad]

Don't have it handy, as I'm on vacation....no FCOMs with me....
BUT: The Bus can be stalled in normal law....yes, it's true, I
promise....if you're on one engine and you have slats/flaps out.
The info is hidden in the bowels of the FCOM.

Second, I'm the type of instructor who has the philosophy that
if a student hasn't learned, the teacher hasn't taught....I always
feel like our training program has failed anytime we have a student
fail or have a problem on the line. In my opinion, the line pilot should
be the last to be blamed. (My position on this, sometimes, really
pisses off my boss.)

Having said that, we, as educators, have failed. For all these years
we've been teaching 'approach to stalls' as if they were actual stalls.
Airbus, now along with the FAA and many U.S. carriers, are making
the distinction. Two different situations; two different procedures
for recovery.

Two weeks ago, Airbus had a meeting in Dubai, and this topic was
discussed. (along with the "new" stall recovery procedure....ha ha ha)

So, what we've been drilling all these years is recovery from the
approach to stall. Now, we're making the distinction...and the 'new'
delineated procedure is for the actual stall.

And, even more to muddy the waters, Airbus states that the
distinction between the two maladies can sometimes be difficult
to determine, even for test pilots. (Assuming that test pilots
are the best pilots in the universe....)

Ya'll be careful out there, ya hear!!!!1

[DozyWannabe]

Oh, that's right, an airbus cannot stall in normal law but can it hit the ground?

Yes, this has been common knowledge for longer than the A320 has been in line service - because this feature of the protections was sadly demonstrated at the Habsheim-Mulhouse airshow, when the PF, having permanently disabled autothrust, tried to pull back on the stick before the engines had spooled up. From his point of view, the aircraft was not responding to his inputs and this was the germ of the "Airbus FBW overrides pilot inputs" complaints that are constantly repeated by his supporters. What tends to be excluded in those complaints - and is something that the PF never draws attention to - is the fact that having irreversibly disconnected throttle control from the computers, his inputs would have caused an unprotected aircraft to stall and fall to the ground in an uncontrolled fashion, with the likelihood that the death toll would have been significantly higher.

Returning to the topic at hand, I think Airbus are doing the right thing by emphatically stating that if you have stalled the aircraft and have altitude to spare the correct action is to get the nose down as soon as possible. This becomes extra important if you have bad airspeed data, because in that situation the stall protections cannot work.

[dovish]

PantLoad,

when you have the time could you please refer to FCOM when it says that an Airbus FBW can be stalled in normal law?

I also share the opinion that Pilots are very bad trained in relation to real stall recoveries. I have never failed to recover an aircraft from a stall situation but have I tried to recover it when I am in severe turbulence with different indications regarding to speed and altitude? Of course not!

"if a student hasn't learned, the teacher hasn't taught" - not always true but very very true!

[LeadSled]

Bloggs,
I think you ( and many others) would be rather appalled at what is required by YSBK CASA office FOI's, in recent times, highly experienced pilots have been failed on base checks for ANY decrease in attitude during stall and recovery. "Powering" out of the stall with zero loss of height has been "informally" adopted as the "standard".

Indeed, one FOI was "demanding" that the stall/attitude warning/stick pusher system in a Metro be deactivated and the aircraft pulled into a "proper" stall ---- only a very very strongly worded letter from the Type Certificate holder dissuaded them/him from the practice.

Maybe some of these "CASA experts" would benefit from a course with UK CAA at Redhill.

Tootle pip!!

[Checkboard]

- 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.

That must be pitch and even then that is a lot--5-10 degrees nose down would be like it. Due to being power-limited, the only means to increase EAS and Mach is gravity.

The information from the AF447 FDR now shows that the aircraft was descending for three minutes with and Angle of Attack of 40º or so - so it should be obvious to see now that, in this type of upset at high altitude resulting in a deep stall, even 10-20º reduction in pitch (OR AoA) may not be enough.

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.

...which is exactly what the AF crew did - maintained the normal after take-off climb pitch (about 15º nose up) with full power for three minutes - and remained stalled until the event ended.

I think you ( and many others) would be rather appalled at what is required by YSBK CASA office FOI's, in recent times, highly experienced pilots have been failed on base checks for ANY decrease in attitude during stall and recovery. "Powering" out of the stall with zero loss of height has been "informally" adopted as the "standard".

Then they are teaching people to die. Stall recovery is exactly that - un-stall the wing, and everything else is secondary (including terrain clearance). Minimising height loss with a stall recovery at altitude is simply not a consideration - if the pilot is so out of the loop that the aircraft has stalled in the first place, then the recovery is going to take some height.

[john_tullamarine]

Powering out of stall MIGHT be adequate on large propeller aircraft - eg Electra and, I would imagine, the Herc would be similar. Certainly, it was fun to do just that on the Electra - a few shudders and away it would go. However, the size of the prop disks meant a sudden and dramatic change in airflow over the wings. It's a bit different with a jet.

The general certification stall recovery is a bit different to the training version - another example of operations not reading the certification stuff. Some aircraft, if held into the stall will do strange things not addressed during certification. The trick is to get the wing unstalled first (and promptly) ... then worry about thrust.

Indeed with a high alpha a heavy handed bunch of thrust might well produce an unwanted and significant nose up pitching moment rather than the nose down pitching moment desired.



Of course, if this is all happening at near dot feet, then one might be advised to incline to minimising height loss on the basis that you are going to die if the stall persists - a case of playing the risk numbers. That is a specific case with priorities different to the general.

[BOAC]

maintained the normal after take-off climb pitch (about 15º nose up) - in which part of the report do you see that? I see 'increasing above 10 degrees'

[Chris Scott]

BOAC,

I think you are referring to the initial increase in pitch, at the start of the upset sequence?

Quote from the English version of the BEA "Update":

"The airplane’s pitch attitude increased progressively beyond 10 degrees and the plane started to climb. The PF made nose-down inputs and alternately left and right roll inputs."

The initial increase in pitch is not explained. At that stage, the BEA does not report any sidestick input.

The aircraft climbed from FL350 to FL375. At that stage, the BEA continues:
"At 2 h 10 min 51, the stall warning was triggered again. The thrust levers were positioned in the TO/GA detent and the PF maintained nose-up inputs. The recorded angle of attack, of around 6 degrees at the triggering of the stall warning, continued to increase. [...]
Around fifteen seconds later, [...]. The PF continued to make nose-up inputs. The airplane’s altitude reached its maximum of about 38,000 ft, its pitch attitude and angle of attack being 16 degrees."

Without wishing to put words into anyone else's mouth, I think the last two sentences may be what Checkboard was referring to.

Chris

[spin_doctor]

Putting aside all talk of whether the Airbus can stall or not, is this change to the stall recovery procedure not, in fact, applicable to all jet types? I had understood it as a joint change by both Boeing and Airbus, possibly others as well.

In my airline all types have adopted the new recovery technique, not just airbus fleets.

[BOAC]

Thanks Chris - indeed - I have already apologised to hyper on t'other thread for missing the conjuction in "pitch attitude and angle of attack".

It would actually help this thread if we could keep the 447 'stall' scenario out of it, since that was a UA event and not what the Airbus notice was referring to. Indeed, a large 'pitch change' was needed there, but is not, as 'willie' suggested, for a 'normal' stall warning when the a/c will not actually be stalled. I would think that had a small nose-down change been possible/made there at 380 from the 4 degrees AoA the a/c would have 'flown' away.

To have a suggestion floating around that you need to bunt 10-20 degrees whenever the stall warning sounds in 'normal' flight frightens me.

[Checkboard]

10-20º is hardly a "bunt". If the aircraft has been mishandled/ignored to the point of stall, I for one would be quite happy to see a firm & positive recovery from the pilots. :cool:

[Microburst2002]

Why would he pitch up?

Maybe indicated airspeed was very high and increasing due to some malfunction of the pitot-static, ADMs, or whatever?

Maybe turbulence and IMC conditions were such that the body feeling was of the airplane being in a steep pitch down (similar to the gulfair crash in the sea after a hand flown visual and go around at night)?

[pontifex]

Reading through all the posts on this subject I am a little concerned by all the references to "deep stall". Of course it is far too soon to really know what went on on the flight deck, we must wait until the true and complete facts are known (if we are to be permitted this luxury). However it is clear that the aircraft descended in a stalled condition. It is likely that this stalled condition could have been recovered from given appropriate control/trim inputs. A deep (or super) stall cannot be recovered from. It almost invariably occurs in a T tailed aircraft in which the airflow off the stalled wing envelops the tailplane rendering it ineffective and with insufficient authority to reduce the pitch attitude and, thus, the AoA. The 340 is clearly not T tailed so I suspect the dirty airflow at, 40 degrees AoA, would have been way above the tailplane which could have been effective.

The T tail deep stall problem was driven into us on the ETPS course with the BAC111 accident on Salisbury plain being the accident that first drew attention to the condition. I know that we were acutely aware of the dangers on the VC10 but were quite happy to take a TriStar well up to the actual stall. Normal, traditional recovery action as I have taught to all my students (and was taught to me from day 1 on the Harvard) worked immediately every time.

Like many others on this thread I have been becoming increasingly concerned that, in the quest for minimising cost, the bean stealers have succeded reducing training to a dangerous level. Surely recovery from a stall must be an instinctive reaction, not a situation requiring reference to the abnormal check list! As an old fashioned QFI (a military flying flying instructor to those unfamiliar with the term) I still think that all students should be taught to recognise and recover from an incipient spin in any attitude, not just the approach to the stall. Meldrew rant now over.

[FlexibleResponse]

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.
nnc0 is offline Report Post Reply

And sadly once again there is NO mention that the ALL-FLYING HORIZONTAL STABILIZER (Airbus call it the THS) might need to be MANUALLY repositioned nose down to regain control of the aircraft in a high alpha situation!

Gentlemen, what the hell is wrong with us? The evidence that we have been given so far by BEA is startlingly clear...why can't we see it for what it is?

I will try to keep this simple.

1. Airbus designed the computer aided flight controls when operating in "normal law" to PREVENT the aircraft from stalling.

2. To achieve pitch control in normal law, the pilots fore and aft sidestick commands are interpreted as incremental (+/-) g commands...until a certain alpha is reached.

3. When that certain alpha (close to the stall) is reached the flight control law becomes an alpha command law so that fore and aft sidestick commands become incremental (+/-) alpha commands...but the flight controls still prevents the aircraft from stalling.

4. IF the aircraft reaches a FLIGHT CONDITION that is outside of the NORMAL LAW flight envelope, the flight controls decide that they must have made some sort of mistake. Therefore in that situation they revert to RECOVERY LAW so that the pilots have full and direct command of the flight control surfaces to be able to recover the aircraft back inside the approved flight envelope (ie, the movement of the sidestick moves the ELEVATORS and AILERONS/SPOILERS directly without refinements).

5. Unfortunately, WHEN the flight controls revert to RECOVERY LAW, the THS FREEZES in the current position.

6. A RED ECAM WARNING tells the pilots "USE MAN PITCH TRIM ONLY".

7. However, with the extreme situation of the aircraft out of control and probable associated and conflicting RED WARNINGS of STALL and/or OVERSPEED with associated AURAL WARNINGS announcing same, it is all too easy for pilots to become overloaded.

8. It is extremely easy for pilots to OVERLOOK the requirement to MANUALLY adjust the THS so that the pilot has ADEQUATE pitch authority to regain control. I have seen that so many times when training pilots in the sim, it makes my head spin.

9. Now in the case of of AF447, BEA has told us that the THS froze at 13 degrees aircraft nose up...and that it stayed at 13 degrees aircraft nose up from 38,000 feet until impact with the sea. It would appear that there was no MANUAL input to the THS throughout the loss of control event.

10. This would indicate that none of the pilots realized that they were trying to control the pitch attitude of the aircraft with the TINY ELEVATOR on the back of the HORIZONTAL STABILIZER which in itself was almost maximum fully trimmed aircraft nose up.

11. They were trying to fly the aircraft with EXTREMELY LIMITED pitch authority.

Yeah I have some thousands of hours flying the A330 and A340 series of this aircraft including training and checking airline pilots and some thousands of hours doing likewise on the A300 and A340 simulators doing same including Jet Upset Training...but what would I know?

[PantLoad]

Fcom 1.22.40 p5

[unmanned transport]

The new 'bullet proof' Airbus stall recovery procedure will be the elimination of pilots from the nose of the 'bus and automation to control the 'craft. How many years 'till that happens is the big question. UAVs are pioneering the way. I am a pilot.

[FE Hoppy]

Flexible Response.

The aircraft responded to nose down inputs:
Around fifteen seconds later, the PF made pitch-down inputs. In the following moments, the angle of attack decreased, the speeds became valid again and the stall warning sounded again.


The problem seems to be that there weren't many of them!

[Yankee Whisky]

Good to come accross someone, Flexible Response, who has the facts as I want to see them presented. I responded some time ago somewhere in this forum questionning the stabilizer position (13-15 nose up) and the resultant ineffectiveness of elevator control input which in the case of AF447 was nose UP, unfortunately aided by the stabilizer position !
Without knowing the condition of the stabilizer trim mechanism, I cannot
suspect a trim failure, such as the AC crash in St Therese, QC, Canada. And why was there no stall recognition by the crew members? Are they so sophisticated that they are no longer stick and rudder pilots? Is this the breed that precedes 100 % pilot function automation?
One might think, though, when the stabilizer trim is frozen, the PF would select opposite stick input, i.e nose DOWN to unstall the aircraft (after all they saw 187 knots on the clock at some point !). Which brings me back to a previous argument in that the sensors are believed to have iced up and I questioned the pitot heat function and this failing on ALL sensors? Not very likely unless there was a total electrical failure, in which case they should have selected the air driven generator?
I am anxiously awaiting the final report on this accident AND assess if the board of investigators have been non-partial, as some writers would make us believe they are! ;)
I do hope there are extenuating circumstances in favor of the crew, although I am not reading anything in support of this presumption, so far.
And then one final point; why are all these "INTERIM" reports being released PRIOR to final analysis AND agreement between investigation members?
I am an old pilot with no AB experience. A "stick and rudder chap" who can still land a Birddog in a three point stall landing!

[DozyWannabe]

FlexibleResponse:

Recovery Law?

This is news to me - as far as I'm aware there is only Normal, Alternative 1, Alternative 2, Direct and Abnormal Attitude...

[FlexibleResponse]

RECOVERY LAW...sorry, perhaps I should have said ABNORMAL ATTITUDE LAW...(see your FCOM).

Forgive me, I am getting old ...my memory is fading...

But please don't lose my essential message in the semantics.

The STABILIZER stopped at 13 degrees (aircraft nose up) when the new flight control law was encountered. This LIMITED the pitch control power (authority) that was available to the pilots to reduce the pitch attitude (and thereby reduce Alpha). This made the chances of recovery of the aircraft from uncontrolled flight UNLIKELY or IMPOSSIBLE.

In essence I am saying:

1. The STABILIZER (which in normal law continuously trims automatically) FROZE at 13 degrees.

2. None of the pilots realized that it had stopped auto-trimming.

3. None of the pilots realized that the MANUAL PITCH TRIM WHEEL HAD to be manually repositioned so that the the aircraft could be recovered from uncontrolled flight.

4. Why the pilots didn't realize and act upon the MANUAL use of the PITCH TRIM WHEEL is the heart of this accident investigation.

[twinotter89]

When frozen water blocked the the AoA vanes of the XL Airways A320 near Perpignan during a demonstration flight the THS got "stuck" at the maximum nose up position. The Pilots tried to controle the plane, but were not aware of the manual trimming required.

[Dalex64]

But if they didn't try to push the nose down, they wouldn't know how much or how little authority they had.

From the looks of things, the pilot only put the nose down once, and the airplane did accelerate over 60kts, which then re-activated the stall warning.

From then on out it looks like the stick was held back, nose up.

It doesn't seem to me that a lack of an attempt to use the manual pitch trim was a factor, as they didn't try a nose-down stall recovery that may or may not have worked due to the trim setting.

[rgbrock1]

FlexibleResponse:

But WHAT caused the horizontal stabilizer to be at 13 degrees?
I understand the freezing part but WHAT is just as vital.

[DozyWannabe]

But WHAT caused the horizontal stabilizer to be at 13 degrees?
I understand the freezing part but WHAT is just as vital.

The truth is that we don't know yet, but it's looking likely that the THS was trimmed in response to pilot input (in Alternate Law 2, autotrim follows the sidestick commands when the limit of elevator authority is reached).

The important questions that raises are:


If that is the case, why did the PF command and hold full back-stick in this manner?
Did the pilot know that doing so would cause the trim to move once the limit of elevator authority had been reached?
Did the pilot know that all it would take to remedy that part of the situation would be to wind the manual trim wheel forward (which disengages autotrim permanently for the flight)?

[wes_wall]

Why the pilots didn't realize and act upon the MANUAL use of the PITCH TRIM WHEEL is the heart of this accident investigation

In the other thread, someone enphatically posted that it was their company policy which strickly forbidden the manual use of the Pitch Trim Wheel. In fact, you were in danger of loosing your job if you touched it. Very strong position was taken on the subject.

Seemed strange to me.

[Microburst2002]

could it be a THS jam, in addition to the pitot-static system?

What was the attitude and indicated airspeeds when AP disconnected?

[dovish]

The THS did not jammed. The THS stopped moving because the aircraft entered in Abnormal Attitude Law. In this law the only way to move the THS is manually.

In the report I did not find what was the attitude and speed when AP/ATHR disconnected.

[john_tullamarine]

The interest in THS position is very important.

Certification stall testing is run with the trim appropriate to a speed a small margin above the stall. With full/near full nose up trim, the crew might find themselves playing test pilot on the day it stalls out of left field ...

[Machinbird]

If I may join the discussion.
Who here has experience flying the A330 (either simulator or real life) in ALT 2 law? Did you ever practice/experience this configuration with a lateral imbalance? I'm trying to figure out if the AF 447 PF might have had serious problems with controlling the roll axis to such an extent that it interfered with pitch control.
Useful collateral information would be how much force is required to achieve 2/3 lateral stick deflection or full lateral stick deflection. I think you can see where I am going with this.
If you will remember, ALT 2 law operates with the roll channel in Direct law.
I've never been in a Bus's cockpit, so I need some knowledgeable feedback in this area.
Thanks.
Mb
PS Found some data from an old post on A320 stick forces. Wouldn't A330/340 stick forces be comparable?

For A320 from 2004 post by 'Max Angle'

The figures copied from an Airbus publication and converted from horrid Euro units to pounds are:

Breakout force: 1.1 pounds

Pitch: Fore and aft. +/- 16 degrees 22.5 pounds

Roll: Outboard 20 degrees 5.6 pounds.

Roll: Inboard 20 degrees 7.8 pounds.

Note that the force is different for inboard and outboard roll. Airbus found during development that your arm is stronger moving inboard than outboard and fine tuned the forces to make left and right roll feel the same. Try moving the stick left and right holding it from above next time you are at work, you can clearly feel the force difference.Just ran some experiments using a scale.
With steady lateral force in the 7 pound range using 1 finger, I wouldn't want to do that much more than 30 seconds. Three to 4 fingers can generate this level of force much more comfortably. I'm wondering if the AF 447 PF felt the need to "palm" the stick. That might explain an involuntary climb.
Instead of rotating the wrist, he might have used the wrist 'curling action to move the stick on the roll axis.

[FlexibleResponse]

FlexibleResponse:

But WHAT caused the horizontal stabilizer to be at 13 degrees?
I understand the freezing part but WHAT is just as vital.

rgbrock1,

Sorry, I used the term "freezing" in the English English sense as opposed to American English. I meant to say the stabilizer stopped working automatically and maintained its last position at 13 deg because of the change of flight control law to ABNORMAL ATTITUDE LAW.

The reason the STABILIZER was at 13 degrees was the zoom climb performed by the PF to pull back and climb to 38,000 feet from cruise altitude, which traded the kinetic speed energy at cruise to potential energy of height gain (and consequential speed loss).

The stabilizer happily auto-trimmed more and more nose up during this manoeuvre as speed was rapidly lost until the aircraft sensed at least one of the extreme parameters that activated ABNORMAL FLIGHT LAW. That event stopped the stabilizer where it was at that instant.

From that moment, the fate of AF447 was sealed unless one of the pilots re-trimmed the stabilizer to the NORMAL RANGE range.

What is the NORMAL RANGE?

NORMAL RANGE for STABILIZER

1. Preflight - 4 deg NU
2. Takeoff Range - Approx 4 deg NU
3. Cruise range - 0 to 2 deg NU

MAX RANGE for STABILIZER

1. Maximum NU - 15 deg NU
2. Maximum ND - 4 deg ND

The detail is all from memory and anyone who is current on type should feel free to correct me.

[rgbrock1]

Thanks for the explanation FlexibleResponse. 'Preciate it.

[FlexibleResponse]

If this report is correct, then there goes another theory on why the THS remained at 13 deg NU until impact...

Stalled AF447 did not switch to abnormal attitude law (http://www.flightglobal.com/articles/2011/06/01/357394/stalled-af447-did-not-switch-to-abnormal-attitude-law.html)

[surplus1]

Disclaimer: I've never been in an AirBus cockpit or simulator. I'm just a retired airline pilot.

FlexibleResponse - Don't give up so easily.

I have no idea why AF447 "did not switch to Abnormal Attitude Law", especially since the BEA release appears to indicate that the parameters that should cause this were in fact exceeded. So, if it didn't - why not? Was this just one more failure of the infallible computers to act as expected?

If on the other hand it did go into Abnormal Attitude Law, was there a failure of the sytem to record that fact? How do we know if it failed to go or merely failed to record that it did?

If the computers behaved as programmed, then why did the THS reach 13 deg NU and stay there for the remainder of the event?

The assumed answer is: The pilots continued to apply and hold full or near-full NU control stick. Why? Because they "didn't know it was stalled"?

As a simpleton, I don't buy it. It doesn't matter whether they knew it was stalled or they didn't. They certainly knew they were descending at a rapid rate, whether or not they had accurate IAS or no IAS at all.

If they (or PF) were continuously applying NU control input - and it obviously was not changing the situation - would they just sit there and not try something (anything) different - such as opposite (ND) control input? My concept of "logic" just doesn't seem to be working in this tale of tragedy.

Did they also lose all attitude references, altimeters and VS indicators as well? It appears they did not. They couldn't observe an apparent 16 deg nose up attitude? They somehow believed that would keep them in level flight and not cause a significant loss of airspeed (even if they couldn't read the airspeed tapes)?

I mean, according to what we are told, they were in level flight - cruising. They lost airspeed indication - for whatever reason(s). Their AP/AT disconnected. Would that change the a/c attitude all by itself. Why?

Is there something in the systems that would cause the THS to move towards NU, or for that matter ND (before the AP disconnected) as a consequence of the loss of reliable airspeed data? .

Based on what I've read so far, there's a huge fly in the ointment somewhere that none of us seems to fully understand. It doesn't compute! <pun intended>

At some point I hope we get enough information to reasonably understand what might have ocurred on that fateful night.; why two fully qualified pilots were apparently unable to maintain level flight in a fully functional aircraft that has lost no more than the input from its pitot tubes (if that is in fact proven beyond doubt). Why it would seemingly "zoom up" some 3000 ft without them noticing or doing anything to prevent/correct/stop it? It just doesn't make sense to me and I'm not ready to crucify them until we know much more.

Meanwhile, me thinks this aircraft was somehow [I]automated out of existence.

[Checkboard]

I have no idea why AF447 "did not switch to Abnormal Attitude Law", especially since the BEA release appears to indicate that the parameters that should cause this were in fact exceeded. So, if it didn't - why not?

The only parameter to trigger Abnormal Attitude Law which was experienced by AF447 was the Angle of Attack - however before the AoA reached the limiting value, the air data was disregarded as unreliable by the system. The other parameters required to trigger Ab. Att. Law (50/120 degrees pitch/roll) were never met.

[BOAC]

MODS!

Please - we don't need 3 threads on the 447 crash!

[dovish]

When the aircraft first reached 60 kts it could go directly to Abnormal Attitude Law.

Then the AoA which is independent of the AirDataComputer (speed) should have triggered the Abnormal Attitude Law.

Why when we have Unreliable Speed we do not disregard the AoA warnings?

Am I missing something here?

[Sciolistes]

If they (or PF) were continuously applying NU control input - and it obviously was not changing the situation - would they just sit there and not try something (anything) different - such as opposite (ND) control input? My concept of "logic" just doesn't seem to be working in this tale of tragedy.
The reason why they failed to recover? I don't know, even with full nose up trim full forward stick would have significantly reduced the AoA. One thing I am sure of though, when I ask Captains what the unusual attitude recovery recall is, I seldom get the right answer. It seems to me that everybody knows how to reject a take-off, deal with an engine fire etc. But I have never had unusual attitude recovery on a sim syllabus and because it isn't practiced most guys seem to forget it is there in the back of the Boeing QRH. Perhaps a similar issue with Airbus trainng?

Maybe the thrust being retarded to idle is a clue that somebody started to try and resolve the situation, but if so it seems hard to explain why full nose down stick wasn't maintained.

[john_tullamarine]

I have to agree with BOAC. This thread has morphed from stall considerations to being a subset of the main one.

Probably best to close it and keep the discussion in the one pot.