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Old 30th May 2011, 08:35   #41 (permalink)
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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.

Last edited by BOAC; 30th May 2011 at 08:47.
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Old 30th May 2011, 11:23   #42 (permalink)
 
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10-20 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.
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Old 30th May 2011, 12:38   #43 (permalink)
 
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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)?
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Old 30th May 2011, 14:32   #44 (permalink)
 
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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.
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Old 30th May 2011, 17:10   #45 (permalink)
 
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Quote:
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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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?
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Old 30th May 2011, 18:48   #46 (permalink)
 
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Fcom 1.22.40 p5

Fcom 1.22.40 p5
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Old 30th May 2011, 23:07   #47 (permalink)
 
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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.
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Old 30th May 2011, 23:21   #48 (permalink)
 
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Flexible Response.

The aircraft responded to nose down inputs:
Quote:
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!
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Old 30th May 2011, 23:44   #49 (permalink)
 
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Angel New Airbus STALL RECOVERY procedure

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!
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Old 30th May 2011, 23:46   #50 (permalink)
 
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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...
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Old 31st May 2011, 03:32   #51 (permalink)
 
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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.
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Old 31st May 2011, 16:28   #52 (permalink)
 
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same as for the XL Airways/AirNZ A320

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.
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Old 31st May 2011, 17:27   #53 (permalink)
 
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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.
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Old 31st May 2011, 19:41   #54 (permalink)
 
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FlexibleResponse:

But WHAT caused the horizontal stabilizer to be at 13 degrees?
I understand the freezing part but WHAT is just as vital.
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Old 31st May 2011, 19:50   #55 (permalink)
 
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Quote:
Originally Posted by rgbrock1 View Post
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)?
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Old 31st May 2011, 20:25   #56 (permalink)
 
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Quote:
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.
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Old 31st May 2011, 20:41   #57 (permalink)
 
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could it be a THS jam, in addition to the pitot-static system?

What was the attitude and indicated airspeeds when AP disconnected?
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Old 31st May 2011, 23:27   #58 (permalink)
 
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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.
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Old 1st Jun 2011, 00:16   #59 (permalink)
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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 ...
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Old 1st Jun 2011, 01:33   #60 (permalink)
 
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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'
Quote:
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.

Last edited by Machinbird; 1st Jun 2011 at 02:39. Reason: adding data on stick force requirements & experiment
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