AirAsia Singapore-bound A320 Missing

[dodgy-alan 1,587]

I bet its got everyone looking at their training systems to make sure it's not repeated. I daresay Airbus will be interested to find the ecact cause as well.

[ddavid 149]

Is there any similarity to the Air France crash, last year? Didn't that ascend very quickly and then the pilot lost control?

Cheers - Dai.

[allardjd 1,853]

It is superficially very similar to the AF447 crash at this point but a lot is not known, including the cause of the climb/pitch-up, what role the computer played and what the pilots did once the computers threw up their hands and dropped out of "normal law".

 

It is especially too soon to point any fingers at the performance of the aircrew.  The pilots in AAF 447, particularly the guy in the right seat, were totally culpable in not recovering from a recoverable situation.   That can't be said about this one, one way or the other, with the information now available.

 

John

[allardjd 1,853]

 I daresay Airbus will be interested to find the ecact cause as well.

 

 

As is usual in these things, Airbus and their insurers are hoping it's an operations, training or maintenance issue; the airline and its insurers are hoping it's a design issue.  The lawyers are hoping that it's at the feet of whoever has the deepest pockets.  In the end, only the lawyers win.

 

AF447 looms, but it's not yet possible to say how relevant that is, beyond the fact that, like AF447, the Indonesian AC appears to have fallen from great height while stalled after flying into ITCZ WX.

 

John

[allardjd 1,853]

"One month after the accident we will just make a preliminary report. No comment and no analysis," Tatang Kurniadi, chairman of the National Transportation Safety Committee, told reporters."

"This will not be exposed to the public. This is for the consumption of those countries that are involved."

...and they wonder why we speculate.

http://www.reuters.com/article/2015/01/21/us-indonesia-airplane-idUSKBN0KU09X20150121

[Bruce (a.k.a. brian747) 142]

Going back to the aerodynamics, reading the preliminary comments has increasingly put me in mind of the discussion about stalling in D.P. Davies's book "Handling the big jets", which to my mind is still the best textbook on the handling qualities of jet aircraft. The author spends 19 pages of chapter five discussing the aerodynamics of stalling, with particular reference to the super-stall, and concludes the section with this strong recommendation:

 

"If ever the day should come when you are faced with a choice of stalling, or doing something else, choose the alternative. It cannot be put too strongly. Whatever you do, don't stall the aeroplane."

 

Although, given freak weather conditions, it may be that the pilots didn't have that alternative, of course.  

 

I fear that the stall which is now being spoken of could indeed be a super-stall (a.k.a. 'deep stall' or 'locked-in condition') — "from which recovery is not possible", according to Mr. Davies (a former Chief Test Pilot of the British Air Registration Board for many years, who it is said has "flown significant flight trials on more individual types of jet transport aeroplane than anyone else in the world"). The discussion in the book is far too extensive to attempt to summarise here, but one long and extremely chilling sentence encapsulates the grim reality of the outcome:

 

"There is no point in discussing the irrevocable case any further, except perhaps to say that those aeroplanes which have been lost in such manoeuvres finally reached the ground —

 

substantially level laterally, having defied all attempts to roll or spin them out of the stabilised condition;

 

only slightly nose down in pitch, with little or no forward speed;

 

at an extremely high incidence;

 

rotating only very slowly in yaw;

 

with (in one case) all the engines flamed out because of being exposed to such massive angles of incidence;

 

and finally, with an enormous vertical velocity."

 

 

(The last three words being the most chilling of all...).

 

 

> "Still doesn't explain the apparent loss of airspeed though...."

 

I fear that the item in the grim list above which speaks of "little or no forward speed" might have something to do with it, Micke.    

 

 

 

 

 

 

 

[allardjd 1,853]

> "Still doesn't explain the apparent loss of airspeed though...."

 

 

Don't ignore the possibility of frozen or otherwise inoperative pitots and/or AoA vanes.  It's not possible to say yet if that occurred or not but it's certainly on the list of possible initiating events.  

 

If incorrect indications from those sensors were consistent with overspeed, the computer would raise the nose to prevent that.  Loss of airspeed indication is recoverable, but if the computer is still in command it may be that it will put the plane into an unrecoverable situation (or at least one that is very difficult to diagnose) before descending into Alternate Law or one of the lower levels of flight control programming.  By definition, stall protection is lost in Alternate Law and practically speaking, is lost when sensors give certain bad information.

 

Pitch trim, which might very well have been run to the nose-up limit by the computer in an attempt to stave off a sensed but fictitious overspeed event, does not restore itself to a more normal configuration upon descending into Alternate law or a lower regimen.  The pilots must do that manually if it is called for.  By then, as your author suggests, it may already be too late.

 

All that is speculative but it's one possible explanation for how the loss of airspeed.

[Bruce (a.k.a. brian747) 142]

> "... it's one possible explanation for how the loss of airspeed."

 

Agreed, John. But it's a nightmare scenario whichever way it went, though.

 

 

[allardjd 1,853]

...it's one possible explanation for how the loss of airspeed.

 

 

oops, made a little grammar error there, didn't I?  I hate it when that happens.  Sorry.

 

John

[allardjd 1,853]

There's a new piece of interesting info.  A leaked radar plot from the Indonesian Department of Transportation shows the flight path and altitudes from just before the event until radar contact was lost at about FL240.  At the very end there's a tight spiral of almost 360 degrees, to the left, with a very high descent rate.  There are a lot of possibilities for this, spiral descent, spin, in-flight break-up and bad data all come to mind.  

 

It's too early to say what it means and the FDR will unravel everything but for now it's an interesting tidbit.  

 

I'm pretty sure spinning an A320 in IMC at FL240 would be a memorable experience, but not a lot of fun.  I'm thinking a change of underwear would be part of the standard kit for that little maneuver.

 

John

 

[J G 927]

The talk of stalling here reminded me of the issues that the BAC 111 had in its early stages.

 

The 111 had rear fuselage mounted engines and a wing that was a fair way back on the body of the aircraft. This meant that as the aircraft climbed, there was a critical angle of attack where the vortex of air coming off the wings was present at the air intakes of the engines.  This caused a fast reduction of airflow into the engine and thus a flame out occurred.  The aircraft quickly stalled and with no power to recover the stall a crash was inevitable.  The aircraft fell out of the sky tail first with no airflow into the engines possible and no chance of a restart.

 

On analysis of recorded flight data (things were basic back then) it was understood that a stall caused the crashes, but not why.  To understand what was happening, a large parachute was mounted on the back of the rear of the aircraft and a test pilot deliberately put the aircraft into the unrecoverable stall situation. Once the aircraft was sliding  back in the stall the parachute was deployed, pulling the tail of the aircraft up and repositioning the aircraft into a conventional dive from which it could be recovered.

 

 

Look carefully at the above photo and you will see the parachute contraption on the ground just beyond the rear stairs.

 

What is the point of the above waffle? Well it seems to me that the airbus could have suffered the same thing, but not from a design fault, rather from a freak and very powerful blast of wind within the storm system that it entered.  I am just speculating here (yes I know I said we shouldn't in an earlier post, but if you cant beat them  - join them!    ) but it seem to me that if the aircraft moved into a column of very rapidly ascending air, then it could have been forced into a nose up position.  if the ascending air was powerful enough it could cause a negative air flow over the wings and into the engines. Result: Same as the BAC 111, a stall and a flame-out of all the engines with no hope of recovery.

[Christopher Low 63]

If civilian airliners and thunderstorms were Venn diagrams, then they would be mutually exclusive. I know that I will be criticised for a statement like that (bearing in mind that thunderstorms occur on a regular basis in certain parts of the world), but that's how I feel.

[britfrog 180]

being an ex-pro I will add a little bit here but await the cvr translation.

 

John the circumstance that you are referring to is called deep stall it can be suffered by any T tailed a/c it is what happened to the trident that crashed near Staines some years ago , I learnt about it at an early age flying B727's however it cannot happen to a conventionally tailed a/c

 

From the info that has bled out so far it would appear that there is no doubt that the airbus climbed (for what ever reason)  at a rate that may have been uncommanded , but for too quickly for his already abnormaly low airspeed, leading to a stall , spin, and inflight breakup., however for this to happen they must have taken it out of normal law into alternate law, or abnormal alternate law

 

You have to remember as a PPL you practice recovery from unusual attitudes, as well as slow flight , stalls, stall awareness , spins,  etc etc

none of which you practice as a captain of a modern airliner, except on the very odd occasion in a simulator because airliners are not designed to take that kind of abuse. Everything you do in an airliner has to be done "by the book" and woe betide anyone who thinks they can get away with doing it otherwise.

Airliners are stressed to plus 4g , minus 0g so if you do get into a spin best to keep the blue side up, as the moment it rolls on its back it falls to pieces basicly

 

this video will show you how an airbus compensates for stupidity

 

 

 

[ddavid 149]

Thanks for the normal/alternate law info, Nigel. After reading a bit about this (Wiki etc) I'm not clear as to whether changing modes - from normal to alternate, say - is automatic, by the flight computer system responding to external inputs (attitude, airspeed, etc) and actuator/sensor failures, or by the crew. I guess I need to read more - and p*ss about with helicopters less!

Cheers - Dai.

[allardjd 1,853]

Dropping out of normal law is normally an automatic response by the computer to a set of inputs or a situation that it cannot resolve or deal with.  That can be initiated by physical damage to the AC, severe WX upset, compromised sensors and probably a half-dozen other things.  

 

The frozen pitots on AF447 caused bad data to be input to the air data computers and the result was an automatic descent from normal law to one of the various flavors of alternate law, resulting in loss of automatic stall protection among other things.  After that happened, the guy in the right seat held his sidestick full-back, stalling the AC with no software protection to prevent it, and essentially held it there for the rest of his life.   I believe the CVR transcript indicated that "Bitchin' Betty" warned "Stall" something like 75 times on the way to the ocean surface, but he still held it full back.

 

I don't know for sure, but don't think that the pilots CAN manually take the AC out of normal law.

 

For the record, neither the A320 nor the A330 (AF447) are T-Tailed, so Nigel's deep-stall description, though accurate, is not applicable here.  I'm pretty sure he's referring to the BAC-1-11 situation that JG posted.

 

John

 

 

[britfrog 180]

John you can turn off each or all of the flight control computers on the rhs of the overhead panel, if you turn them all off you are left with elavator trim and rudder as your sole source of control , but this is only if you have hydraulics ---

no hydraulics and no computers means that you have just about enough time to put your head between your legs and kiss your ass goodbye.

 

I dont know if any of you have ever been on the flightdeck of an airbus , but it is much smaller than say a boeing 737, if you are tall , like myslf it is not easy to get into the rh seat and it has been documented on more than one occasion the rh seat occupier has accidentally turned off the flight control computers by accident , with his head when trying to regain his seat in turbulence, which lead to much headscratching for a few minutes.

[hurricanemk1c 195]

When I went into an A320 cockpit, I found it larger than a 737 cockpit. Just a personal observation.

 

As for this accident - it's sad but my main feeling was weather

[allardjd 1,853]

@ Nigel - I stand corrected.  I guess that does constitute taking the AC out of Normal Law manually but it's a severe way to do it.  Doing so bypasses Alternate Law, Abnormal Alternate Law and Direct Law, putting the AC into what is called Mechanical Law.  As you say, in that mode you fly it with elevator trim and rudder only. No ailerons, spoilers, speed brakes, etc.  Not a nice thing and probably not something Airbus drivers get much practice at, even in a simulator.

 

John

[hlminx 301]

Still seems odd to me that the entire list of those on board was posted online within hours for anyone to read and yet the authorities aren't publishing the preliminary report..

[allardjd 1,853]

It's simple. The pax list doesn't carry the risk of making anyone look bad.

 

John

[hlminx 301]

Think you just hit the nail on the head John..

[allardjd 1,853]

The stall warning - an automated voice that repeats the words "stall, stall" - had sounded in the cockpit. The aircraft was still in a stall when the black box recordings ended seconds before impact, Siswosuwarno said.

 

 

 

From the Indonesian authorities...  This is looking more and more like AF447, however neither the initiating event(s) nor whether one of the pilots held the stick back during the stalled descent as in AF447 are yet publicly known.  

 

It does appear that it fell from great height, fully stalled with little forward speed.

 

John

 

 

[britfrog 180]

the plane cannot stall if flown under normal law, however the truth will out as it may turn out that the already highly criticised piot tubes may have frozen up

[allardjd 1,853]

One of the guys at PPRUNE described a scenario where pitots ice early in a climb.  Subsequently, the "trapped" air in the pitot side, which is constantly being compared to the pressure of the potentially un-iced static port side of the instrument, appears to be increasing in pressure, i.e. speed increasing. What is actually happening is that static pressure is decreasing because of the increasing altitude, but all the instrument knows is that the dp is increasing, which it can only interpret as an indication of increasing airspeed.  The computers, unless they have figured out that the pitot data is unreliable, raise the nose to prevent a false overspeed condition and you get a classical "diverging" situation, where the worse it gets, the worse it gets.

 

As far as I know there's no indication yet whether they were still in Normal Law or not, but if the air data is unreliable, stall and overspeed protection don't really mean much, even if still in Normal Law - GIGO.

 

They also described some kind of icing that can occur at high altitudes in the tropics - not quite the same as super-cooled water droplets, but some other name I don't recall.  The first ice that hits the pitot is already frozen but briefly melts and spatters, then instantly crystalizes again and creates a layer that more ice can build on.  According to him there are cases where this can overwhelm even well designed pitot heat systems.

 

John

[allardjd 1,853]

http://www.airlive.net/2015/01/breaking-pilots-of-airasia-qz8501.html

 

The pilots of AirAsia Bhd. Flight 8501 cut power to a critical computer system that normally prevents planes from going out of control shortly before it plunged into the Java Sea, two people with knowledge of the investigation said. 

 

The action appears to have helped trigger the events of Dec. 28, when the Airbus Group NV A320 plane climbed so abruptly that it lost lift and it began falling with warnings blaring in the cockpit, the people said. All 162 aboard were killed. 

 

This sounds like leaked information, so should be taken with a grain of salt.  If true, it could suggest that the crew may have been trying to get more direct control of the aircraft by dropping into Direct or Mechanical Law.  If they really did that and did it intentionally, that's an indication that they were in pretty dire straights.

 

Still lots to chew on yet, and having had the recorders for two weeks, somebody knows a lot more than they are willing to publish at this point.

 

John