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Air Asia Indonesia Lost Contact from Surabaya to Singapore

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Air Asia Indonesia Lost Contact from Surabaya to Singapore

Old 5th Feb 2015, 13:11
  #3061 (permalink)  
 
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No. When you apply full forward stick you get full elevator travel, at least until the lower G limit of -1 is reached. If you manually move the trim wheel, automatic stabiliser trimming stops for a period of time. Hence, a little nose down stab trim can be a bad thing if the pilot then subconciously is relying on the FBW to complete the THS nose down travel.

In the very high AOA cases they claim there is no valid data set upon which to build a sim model. Yet Airbus used a sim to model the AF447 flight. From that experience they changed the stall recovery to include the selection of flaps one below FL210, the goal being to extend slats, thereby decreasing the net angle of attack. They also noted an improved stall recovery with manual stab trim, exactly as in almost every modern transport jet.

We used to go decades without hearing of a stall accident. Now it seems to be weeks. What gives?
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Old 5th Feb 2015, 13:38
  #3062 (permalink)  
 
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Post 3069 - Leightman 957

In the early 80's I believe NASA did some testing of deep stall characteristics using a single place T tail Schweitzer 1-36 which was modified to permit the horizontal stab to angle nose down to about 45 degrees. The pictures of tell tail streamers angled up about 45 degrees to the wing mean chord in a steady stable descent was arresting.
http://www.mediafire.com/view/sdwzcc...ll-nasa-03.jpg
http://www.mediafire.com/view/2sa52g...l/Capture5.PNG
http://www.mediafire.com/view/2t762l...28129_full.jpg
http://www.mediafire.com/view/idkla5...26847_full.jpg
http://www.mediafire.com/view/d62mdh...26845_full.jpg
http://www.mediafire.com/view/fq4874...ain_H-1242.pdf
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Old 5th Feb 2015, 14:06
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Deep Stall

When the AF accident took place I went to the sim to reproduce the accident.

35000 ft ,ALTN LAW , pitch up , gained altitude , until stall.Once the airplane was completed stalled , with R/D nearly 10000ft/min , started recovering.

As per manual. Nothing . Tried a few times with and without power but with sidestick ALWAYS full forward. Result: crash.

There is only wat to get out of the stall.Keep the sidestick full forward and imediatelly manually pitch down the trim wheel.Very fast. And then you recover at about 20,25 thousand feet.

Furthermore:

Airbus blames it is impossible to stall the airplane in NORMAL LAW. IT isn`t. It is possible and it already happen without consequences.
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Old 5th Feb 2015, 14:15
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Did you throttle back, or bank the a/c 90 degs, or lower the gear etc., to try and get the nose down? If so and were unable to recover as you have written, the a/c should not have been certified in it's present state, IMHO.

Was the appropriate high altitude stall data programmed into the simulator?
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Old 5th Feb 2015, 14:19
  #3065 (permalink)  
 
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Originally Posted by Ventus45
What good would that do ? If "the system" wants 1g, if you trim the THS nose down, won't it just keep feeding in up elevator to counter you, until it is finally full up ? By that stage you will have far more THS nose down trim than is healthy. Might you then be in a worse place than from whence you came ?
Are you for real? 40 AOA, full power, 10 nose up descending at 10,000ft/min all the while banking/turning and you think the FBW will be trying to give you 1g? In any case, a full nose down stab+full nose up elevator is bound to be better than the other combination when you're trying to get out of a stall if the silly FBW is opposing your full nose-down stick input...
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Old 5th Feb 2015, 15:00
  #3066 (permalink)  
 
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Was the appropriate high altitude stall data programmed into the simulator?
I don`t know if the sim really reproduces the airplane bahaviour. But it is supposed to do it.
Despite I think test pilots never took the airplane to such conditions in order to see it.
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Old 5th Feb 2015, 15:05
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Thanks for your input. I don't think they did either.
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Old 5th Feb 2015, 15:56
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post 3061 - RetiredF4
Quote:
And if the full forward stick does not lead to the desired reaction, feed in manual trim.

Quote Ventus
What good would that do ? If "the system" wants 1g, if you trim the THS nose down, won't it just keep feeding in up elevator to counter you, until it is finally full up ? By that stage you will have far more THS nose down trim than is healthy. Might you then be in a worse place than from whence you came ?
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The system wants, what is demanded by the SS position. Therfore the positioning of the SS to nose down is the first priority. If that works, than fine, but if it does not work fast enough, than the trim most probably is already all the way up.

If we look back to the documented stall accidents we know, that most crews were reluctant to do that in an appropriate way. The ND input was not present at all, was not far enough nose down, not long enough down or accompanied by noseup inputs averaging in an overall nose up input. This inapropriate SS handling may command a loadfactor value greater than the one present while descending in a stalled attitude. The consequence is that the flight computers may drive the elevators and in turn the THS trim to full nose up position.

As long as the elevators are nose up from neutral, the trim will not move afaik despite the SS nose down position. As the certification requirement is -1 and +2.5g, I assume that a full nose down SS input would not deliver more than 0 G (i could not find a reference with the applicable loadfactor demands in relation to the SS position). A controlled manual trim input would assist the SS input and not counter it.

In A320 series the THS trim might have stopped depending on the law reconfiguration, and it might only be available in mechanical mode.

But is there time for error and try?
As I said before, follow the procedure, which says under step 2.b
" Nose down pitch trim .......as needed.
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Old 5th Feb 2015, 17:23
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RetiredF4;
http://www.pprune.org/rumours-news/5...#post8855181As long as the elevators are nose up from neutral, the trim will not move afaik despite the SS nose down position. As the certification requirement is -1 and +2.5g, I assume that a full nose down SS input would not deliver more than 0 G (i could not find a reference with the applicable loadfactor demands in relation to the SS position). A controlled manual trim input would assist the SS input and not counter it.
I concur. Experiments with the A330 sim, (understand the arguments re sim "duplication of stall" and "no-data", etc.), demonstrated that the THS followed SS position; full-ND SS brought a -13 THS setting (the result of an extended NU SS), to approximately -2, recovering the stall in about 45" with a height loss of about 15,000ft. Manual rotation of the trim wheel forward could only help.

IIRC from the Perpignan accident report, the THS stops trimming with a stall warning. I would have to consult the report again to see if a comment or recommendation regarding the use of manually setting the THS would have provided conditions for recovery - they didn't have much altitude to start with...
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Old 5th Feb 2015, 19:25
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On the flip side, I 'spect if one rolled in full nose down manual trim for recovery, one would have a tiger-by-the-tail when and if the stall broke at some 30 or so degrees nose low and accelerating with a limiting 2.5 g available.
Yep, I agree. You would ideally like to dial in a 300 knot trim setting, and only if you absolutely needed it to break a stall would you go to a lower trim setting. But them you better have PNF primed to dial it back pronto as soon as the airspeed begins to accelerate past 200 knots.

Probably better to rock the aircraft out of the stall than to dial in those last few nose down units. More than likely, it would be a quicker and more positive recovery.
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Old 6th Feb 2015, 02:15
  #3071 (permalink)  
 
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Smile 8501

Flaps extension below 20000 or speed brake is the only way to recover
Tested in the sim .. No other inputs will change the turbulent flow .. Perhaps trimming the THS but at 15000 fpm highly unlikely given the severity of emergency and unreliable speed compunded by adr aural warninge and messages . Switching off adr"s and extending the flaps below 20000 and speed brakes , trying to fly pitch n power or BUSS is the only way to recover
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Old 6th Feb 2015, 04:40
  #3072 (permalink)  
 
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Being in a stalled aircraft in turbulence is no fun ,Being in a stalled iced laden aircraft in turbulence in IMC is time to get the QRH prayer mats out.
If you are brave/dumb enough to go into a 50,000 foot CB you will probably be iced up as well and the aircraft deep stall recovery techniques practiced in the sim may not work .
It may need a combination of tail plane ice stall recovery techniques combined with gentle yaw and roll induced by gentle application of rudder to get the gravity working in the right direction to give you relative airflow without overloading the wing or control surfaces.
Keep in mind that any aircraft when it is iced up can be a wobbly thing to control ,and you may encounter some un-commanded pitch ,roll and yaw changes to the attitude that can be confusing .
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Old 6th Feb 2015, 07:53
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Quote:
On the flip side, I 'spect if one rolled in full nose down manual trim for recovery, one would have a tiger-by-the-tail when and if the stall broke at some 30 or so degrees nose low and accelerating with a limiting 2.5 g available.

Quote Machinbird
Yep, I agree. You would ideally like to dial in a 300 knot trim setting, and only if you absolutely needed it to break a stall would you go to a lower trim setting. But them you better have PNF primed to dial it back pronto as soon as the airspeed begins to accelerate past 200 knots.

Probably better to rock the aircraft out of the stall than to dial in those last few nose down units. More than likely, it would be a quicker and more positive recovery.
Rolling the trim to a normal cruise setting or take off setting initially would aid in the recovery and should cause no harm. The change of trim is not instantaneous and the elevators are still controlled by the Flight computers to achieve the loadfactor commanded by the SS. Hence when the AOA comes down to below stall value and the speed builds up, the trim is in the correct range. Imagine what would happen, if the trim would still be in full nose up position at the point of recovery? By increasing speed it gets more effective and kicks the aircraft back into a secondary stall.

MB, i know what you mean by rocking the aircraft out of stall, but i estimate the success rate of a comercial pilot in doing so very low. Same for extending something to change the airflow. Those are last ditch maneuvers with uncertain outcome. Using the rudder without the dampers active or in a degraded mode and no limiter working might brake off the tail.

In AF447 Bonin was occupied by the bank angle, while a healthy bank angle would have helped him to bring the nose down and get the speed back. Anytime the bank angle was greatest, the nose came down, and anytime he managed to level the wings the nose came up again.

The fast jet drivers in an out of control recovery (Spin is different) know not to deal with aileron or rudder inputs until the nose is below the horizon and the speed is building up, only then it is time to correct the attitude by rolling to the nearest horizon. In a comercial aircraft it might be necessary to control the bank angle within a given limit like 45 or 60, but i see no point to level the wings as long as the aircraft is still in high AOA. The High AOA is not a bank angle problem, it is a pitch against flight path problem. That is a point where the new stall recovery procedure is not clear about at least not to my sense of thinking.

If all that normal procedural stuff does not work, then it might be the time to go into test pilots territory and try something outside of the procedure.

Last edited by RetiredF4; 6th Feb 2015 at 09:19.
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Old 6th Feb 2015, 11:01
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I 'spect if one rolled in full nose down manual trim for recovery, one would have a tiger-by-the-tail when and if the stall broke at some 30 or so degrees nose low and accelerating with a limiting 2.5 g available.
I don't think so. 30 nose down pulling at not even 2g starting at say 150KIAS with no power would probably result in another stall, not a wing-ripping-off mega overspeed... The drag at 200KIAS pulling the equivalent of a 60 bank turn is going to require a fair bit of power. You will obviously have to trim back but it wouldn't be a problem in my view.
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Old 6th Feb 2015, 12:02
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We still have the speed/air brakes on this type of aircraft do we not? Or is it a case the computer inhibits the A/B to reduce speed because it's automatic for landing only??
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Old 6th Feb 2015, 16:42
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And Mmo testing.
It's not clear to me that anything less than ejector seats would be an reliable means of escape, particularly if the pilots/engineers were experiencing +/- a couple of g.
I have seen 'Bus test pilots claim that the orange suits and parachutes were mostly a box-ticking exercise.
With a hatch forward of the engines there is a risk of the test pilot causing foreign object damage to the engines! Or would you wait for them to spool down
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Old 6th Feb 2015, 16:42
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One of the pilots had just been recovered

Basarnas has just announced that one of the pilots has been recovered. The pilot was still strapped in his seat. The seat was close to the cockpit. And the cockpit apparently only 20 m (instead of first reported 500 m) from the main fuselage. It is not clear if its the captain or his F/O.

NTSC already reported earlier that the captain was seated on the left and the F/O on the right.

Last edited by A0283; 6th Feb 2015 at 16:56.
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Old 6th Feb 2015, 18:02
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SPD LIMIT

Most probable scenario is :

Captain resetting the FAC's =

Loss of the A/P

Red "SPD LIMIT" appeared on both PFD's speed scale

F/O get confused and tought "SDP LIMIT" is an overspeed warning and thus

pulled up sharply... stalled...
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Old 6th Feb 2015, 18:04
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In other words, lack of appropriate training.
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Old 6th Feb 2015, 19:22
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Pushing over

Uncle Fred: Even having been exposed to some of this training in the sim, I did not really take to heart what it would be like to have to push over that much at 350 and how I would have to be fighting what the body would be telling me not to do.

I know that there are a LOT of posts as far (agreement is probably going too far) to the effect that pushing forward, or anything less than 1.00 positive G is uncomfortable, unfamiliar, non-intuitive, and frowned on by management. But it seems pretty clear that poster opinion agrees that there are circumstances when this action is appropriate and even immediately mandatory. I am excluding airframe G limits and myriad possible computer interactions for the moment because they mislead away from the fact that lack of comfort or familiarity is not an excuse for not doing the right thing. If one never ever practices something but thinks that carrying it around in their head as an intellectual trivia bit for use in extreme situations will be sufficient come the need, the success rate is going to be low. And while evident on the FDR might be plain, they why probably will not at all be apparent on the CVR.

I can't help recalling that WWII German pilots got themselves out of a lot of nasty spots by pushing over. Written about later the reason given was always German fuel injection capability over American carburetor incapability. But it wasn't mentioned that pushing also offered the benefit of being counter-intuitive.

I've spent enough time hanging from a seat harness to know that in addition to the brain drain resulting from all the mixed up kinesthetic sensations, control touch inverted or even in positive sub 1 G can be a much different animal depending on one's personal fright curve. And I have to say that the idea that there are a lot of airline pilots out there with no clue whatever about those differences is alarming if not frightening. Granted it may never be needed, but the idea that a pilot would not only be uncomfortable but also would have no interest in pursuing those aspects of flight outside the norm is not preparedness norm I have always expected of pilots who got farther along than I did. Intellectual knowledge does not equal knowledge plus kinesthetic preparedness. What one is not willing to explore out of cautious self preservation will eventually come as a pop quiz in less than propitious circumstances.
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