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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 4th Feb 2015, 08:00
  #3021 (permalink)  
 
Join Date: Mar 2010
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F4

A neutral stick in the bus commands a loadfactor of 1g, and would therefore force the aircraft in a decreasing speed environment due to power reduction in a higher AOA
You have a stick that commands 'g' instead of attitude??? Who invented that idea? Anyway, surely that is not true in alternate law, it must default to attitude. Yes, no? Surely it must.

But what I said stands true for conventional controls. A good aircraft should always lower its nose in the stall even with the stick neutral. If not, you have the CofG - CofL couple incorrectly positioned. (But see also below.)



Ratherbe:

The pushers were required in these a/c because the stall was unrecoverable. Pushers are not required in a/c that can recover with standard pilot actions.
But this is the question. Is the stall recoverable if the thrust has been left at maximum?

The stall is certainly not recoverable on the 737 (for instance), at low altitude with the engines at max, as was amply demonstrated a few years back on an ILS approach. But what about at high altitude? Ok, thrust may have degraded to about 1/4, at 35,000 ft, but that is still a lot of pitch-couple for the elevators to overcome. So will it recover from the stall at 39,000 ft, with engines at max? My last sim run at this a few years back demonstrated that an underslung twin was reluctant to unstall at full aft CofG at best, and that was not using full chat (we had reduced power, to create the stall).

And if the stall is not easily recoverable with engines at max thrust, then why no stick pusher? (Or why no auto thrust reducer....?)
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Old 4th Feb 2015, 08:26
  #3022 (permalink)  
 
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"When a tail loses lift the nose pitches down because the horizontal stabilizer pushes the tail down for stability."

If the THS is also stalled and thrust is keeping the nose up (high AoA), will that still be the case?
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Old 4th Feb 2015, 08:53
  #3023 (permalink)  
 
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tubby linton
Nigel the latest stall drill in the QRH states--

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.
Suggest you re-read my post re the drill I referred to, and QRH. Mine says "TOGA and set 15nu"...
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Old 4th Feb 2015, 09:39
  #3024 (permalink)  
 
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TOGA and nose down stick.

TOGA and pushing nose down on the stick will get you nowhere in some deep stalls.
The 2 moments neutralise ach other.
The engines lifting the nose, and the tail pushing nose down.

The remaining vector is ZERO and the only velocity is going vertical down till impact.

Stalls come in lots of forms and shapes.

Prio ONE is to get the nose down.

Stick, closing of throttles, trim to nose down, all tools are good tools to get the nose down.

But you have to get them all working together.

At FL, this can take several thousands of feet.
But PRIO ONE is to get the nose down again. Even if it means dropping the gear in airplanes that allow it in the higher FL.

Never mind a missing door, if it can get you to regain control of the aircraft.
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Old 4th Feb 2015, 09:41
  #3025 (permalink)  
 
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Nigel my post was a straight lift from the FCOM regarding a stall warning(not at take off) .
At Take off it is as you say Toga ~15
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Old 4th Feb 2015, 09:42
  #3026 (permalink)  
 
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When a tail loses lift the nose pitches down because the horizontal stabilizer pushes the tail down for stability.
Actually it is not for stability, but for moment compensation. The moment compensated is the nose-down pitching moment produced naturally by any cambered airfoil with attached flow. So when stalled, this pitching moment may disappear, and no more downforce on the tail is required. But that depends heavily on the specific airfoil characteristics, whether the flow separation starts at the trailing edge and extends forward, or whether it starts at the leading edge and reattaches further aft.
At 30° AoA there is no way to produce a down force, no plain flap (used as elevator) is that powerful and nobody would be insane enough to allow a stabilizer trim to move 30° nose down (relative to the fuselage). And as for a swept wing the outer wing is stalled first, there is so much nose up pitching moment that you need lift on the stabilizer to maintain stable flight.
Which however is not always desirable, as stable may mean unrecoverable, so you may prefer to lose control and start again by recovering from there.
Also the characteristic nose drop at stall is produced by the lift produced at the horizontal stabilizer at high AOA.
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Old 4th Feb 2015, 10:16
  #3027 (permalink)  
 
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Nigel my post was a straight lift from the FCOM regarding a stall warning(not at take off) .
At Take off it is as you say Toga ~15
Thanks

It's all a few posts back now, but was in response to a suggestion that a Stall Warning generates an automatic power reduction
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Old 4th Feb 2015, 10:17
  #3028 (permalink)  
 
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Silverstrata,

To my knowledge, no commercial aircraft is ever directly "commanding" an attitude with either a stick or control column.

Conventional aircraft command a pitch change (or attitude) by deflection of the elevator.
Airbus FBW aircraft side stick orders command a g load which, through various flight computers, move the elevator accordingly to give the demanded g load, until the stick is released back to its neutral position, then 1g (corrected for pitch) will be maintained again, until a new input is made on the side stick.

This is valid in pitch both in normal law and alternate law. Roll is another story.
Only direct law will provide a direct relationship between elevator and sidestick longitudinal movements, though not in a strickly linear fashion.

For the rest of these wonders of aviation technologies and why it was designed this way, I recommend that you spend some time in the Tech Log and get a good grip with the concept of Airbus FBW before suggesting this is nonsense, or why would anyone design such a thing.
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Old 4th Feb 2015, 10:24
  #3029 (permalink)  
 
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Well I hope Volume will agree that a lot of swept wings are doctored
to force a root stall first so the mainplane itself contributes to
nose down (-) in and of itself.
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Old 4th Feb 2015, 11:06
  #3030 (permalink)  

Keeping Danny in Sandwiches
 
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I have always been fascinated by the position of the wing on the A320 compared to the 737. It appears to be further forward which would suggest to me that the downforce on the stabilizer of the A320 is less than the 737. If that is the case the aircraft would have less of a natural recovery from the stall than the Boeing. Any thoughts?
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Old 4th Feb 2015, 11:21
  #3031 (permalink)  
 
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I have always been fascinated by the position of the wing on the A320 compared to the 737. It appears to be further forward which would suggest to me that the downforce on the stabilizer of the A320 is less than the 737. If that is the case the aircraft would have less of a natural recovery from the stall than the Boeing. Any thoughts?.............................................


Maybe they have fatter pilots.

Doesn't matter where the wing is in comparison, where the CoG is that matters, and to the CoP
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Old 4th Feb 2015, 11:22
  #3032 (permalink)  
 
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Anyone know what the transit time for the the elevator auto-trim is from the full 13 degrees up back to neutral on the -320 when pushing full forward? That delay is problematic when the brain is racing to solve a problem and acting faster than the systems on the A/C.
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Old 4th Feb 2015, 11:48
  #3033 (permalink)  
 
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I think problematic is not the time of travel of the THS trim, it would move quite fast (when it is commanded by the computers to move) however that depends on the present loadfactor and speed and the gains, and I think there are more factors going into the flight computers which finally position the elevators and move the trim.

More problematic seems to be that pilots over all brands avoid considerable loadfactor reductions to below 1 g by all means, which is good for load comfort during normal ops. Minimal loadfactor reduction below 1 g is only present during day to day ops when initiating a descent or doing a level off after a climb. I trained military pilots in air combat maneuvering, and even this breed is very reluctant to use agressive nose down stick inputs and the more when this input should be maintained for more than a second in the range of 0 to -1g. It has to be trained into them that they gain confidence in the outcome of such inputs. Sure it comes handy to be strapped into the seat and having no meals fly around.

Therefore in a stalled situation it is a total untrained and uncomforting maneuver to put the SS or the control column full forward until the aircraft reacts to the input in the desired way. Looking at the FDR' s from some stall accidents will show my point. It is the thinking " a neutral or slightly nose down input will do the trick" and "negative g's will kill" which is the elephant in the room in failed stall recoveries.

I think especially Airbus crews could do that maneuver without much thinking, as the loadfactor protection is operational in normal and alternate law and should protect the aircraft from too much negative g's. Let the system work for the benefit of a fast and quick recovery instead of taking the chance that it works against this intent. And if the full forward stick does not lead to the desired reaction, feed in manual trim.

Last edited by RetiredF4; 4th Feb 2015 at 13:31.
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Old 4th Feb 2015, 12:46
  #3034 (permalink)  
 
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UPRT

I have recently undergone the Upset Recovery Training developed specifically to train airline crew to recognize and recover from extreme upsets and Loss of Control Inflight ( LOC-I).

I am an Airbus TC on the 320, and I must say, after that program, we are staring at the biggest threat to airline ops completely wide-eyed and unprepared.

This totally redefines the concept of unusual attitude recovery. Hugely.

Thank heavens this has actually been developed, refined and is now actually being implemented. Google UPRT and have a look at the excellent documents available.

Let your management know in no uncertain terms that this must form part of your recurrent program THIS YEAR.

Push. Roll. Power. Stabilize!

Last edited by Jack of All; 4th Feb 2015 at 12:59. Reason: Spelling
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Old 4th Feb 2015, 13:14
  #3035 (permalink)  
 
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So it will take a long time SS full nose down to get those elevators moving beyond the neutral position into nose down, and only then would the trim start to follow and start to trim nose down. There is no time to wait for that. Use the procedure which is established, and that one includes the use of manual trim.
Wow..This autotrim design is at the heart of it.The USE MANUAL TRIM didnt work for test pilots at Perpignan,it will hardly work for the LCD will it now?
If I handfly a B,I rest my thumb on the trim switch.Automatically.I dont think about it.Its a motor function.

An Airbus pilot can probably go a whole line career and never invoke law degradation and so never trim manually except twice a year in the sim.How easy then might it be to forget to use manual trim in a stall with no stick shaker and only that useless "stall,stall" going?Aural warnings get filtered out under stress.ECAM advisories,twenty at a time,not much good either.No stick shaker.Well,there isnt a stick...Nothing tactile,best channel of all under stress.

Trim down,stick down,reduce thrust mid-position..Just how difficult is it?Why the confusion?What can be done?
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Old 4th Feb 2015, 13:26
  #3036 (permalink)  
 
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@Jack of all

Thank you for that link.

Now after all these years of discussion there is hope....!
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Old 4th Feb 2015, 13:49
  #3037 (permalink)  
 
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Speculating

Correct me if I'm wrong, but there are only two ways that the Airbus could have climbed as rapidly as it did: with severe and persistent up elevator or with CG way too aft. We have reports that the CG was well within limits. So that leaves severe and persistent up elevator - something that should not be allowed by the FACs. So we have a problem with either the FACs or the elevator itself. It is reported that both FACs were reporting a fault and that the stall warning was sounding. So it would appear that the FACs "knew" something was wrong and that the plane was in a stall. From this thread, it is reported that the FACs respond to a stall condition by increasing thrust and applying down elevator. It is possible that the FAC software failed in this simple duty, but I would bet against that. Also, if the main problem was with the FACs, then cutting them out should have made the flight recoverable by ATC pilots.
That leaves the elevator itself. If the pilot started a climb, the elevator may have visited a severe up position. If the elevator got stuck in that position, the FACs would signal a fault and the plane would attempt an inside loop and enter a dramatic stall.
But why would the pilots take out the FACs that were already trying to get the elevators into a nose down position? So that they could do something that the FACs were not programmed to do - attempt to shake the rudder free.

Please feel free to poke holes in this notion. That's what I've posted it for.
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Old 4th Feb 2015, 14:01
  #3038 (permalink)  
 
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True Rananım
Haptic feedback is good. Doesn't get filtered out too easily
witness being tapped on the shoulder repeatedly... annoys!
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Old 4th Feb 2015, 14:18
  #3039 (permalink)  
 
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Jack

So good to hear there is actually recognition now of an old problem. How many years and lives lost too late?

This delay is nothing short of criminal.
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Old 4th Feb 2015, 15:08
  #3040 (permalink)  
 
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When a tail loses lift the nose pitches down because the horizontal stabilizer pushes the tail down for stability.
Actually it is not for stability, but for moment compensation. The moment compensated is the nose-down pitching moment produced naturally by any cambered airfoil with attached flow. So when stalled, this pitching moment may disappear, and no more downforce on the tail is required. But that depends heavily on the specific airfoil characteristics, whether the flow separation starts at the trailing edge and extends forward, or whether it starts at the leading edge and reattaches further aft.
.
Actually it is for stability....modern jets are still aerodynamically stable.. I have done the hours and hours of heavy calculations. In essence your wasting fuel ( big wing pulls up, tail down ) by this downward forces, but it's the only way to make the AC naturally stable without computer systems as in fighter jets
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