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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 23rd Jan 2015, 16:21
  #2421 (permalink)  
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I fly the A320, and recently received guidance that when Sparky (the mysterious French brain that protects us from screwing things up) is directing unsustainable nose up or down auto commands, you press off two of the three ADIR push-buttons.

My bible is to turn off all the automation when things start to spin out of control. It will fly like an airplane if you allow it.

With experience (now about 10 years on Airbus), I've found, less and less do I question, 'Why is Sparky doing that?', as I know as soon as I ask myself the question.

One thing I inwardly shudder about, though, is that under the seniority system of the major airlines flying the A320, you can have the situation of a brand new Captain coming from an old Boeing with no Airbus experience, and a new FO who knows next to nothing, dealing with the surprises Airbus will throw at you.
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Old 23rd Jan 2015, 17:21
  #2422 (permalink)  
 
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There is a comment on another forum that uncommanded rudder is suspected. But even if the rudder was at full deflection could this not be counteracted and control maintained through engine power and aileron input?
Full rudder deflection at cruise speed can cause vertical fin separation. The rudder is sized to provide sufficient rudder power to overcome a worst case yaw deflection at or near stall speed. At cruise speed the rudder has enough power to fail the vertical fin. The rudder damper system is (usually) designed to prevent excessive rudder deflection at high speeds in a mechanical flight control system. In a fly by wire system that is taken care of in software. If something went wrong to cause a full rudder deflection at cruise, or worse yet rudder couplets (swinging the rudder at high deflection from one direction to the other) at cruise, the vertical fin will fail. That was the cause of the loss of AA flight 587.
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Old 23rd Jan 2015, 18:39
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YAW on A320

The rudder damper system is (usually) designed to prevent excessive rudder deflection at high speeds in a mechanical flight control system. In a fly by wire system that is taken care of in software.

Yaw damper is designed to "damper" yaw movements not to limit rudder deflection. RTLU (Rudder Travel Limiting Unit) is there to limit mechanically the rudder deflection depending of A/C speed, this units (double) are driven by FAC's fonction of speed information from ADR's.
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Old 23rd Jan 2015, 19:14
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YAW

The rudder is sized to provide sufficient rudder power to overcome a worst case yaw deflection at or near stall speed.
In fact, rudder is sized to cope with VMCG / VMCA. Easy to find what's VMCG/VMCA on the net.
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Old 23rd Jan 2015, 20:39
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Originally Posted by McWho
There is a comment on another forum that uncommanded rudder is suspected.
Doesn't fit this scenario.
At all.
Uncommanded rudder trim would cause a nose down dive and a sharp turn. (Or possibly a fin separation again with a dive and sharp turn)
Here we have a massive climb and at a very wide turn until very late in the event.
So: You can probably scrap rudder trim runaway in this case. Doesn't seem to fit to what we know so far.
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Old 23rd Jan 2015, 21:56
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If boom mics are worn and designed to stay on during severe turbulance! they remain the best solution.
The overhead mounted ambient mics with an omnidirectional pickup pattern cant be expected to recieve the pilots voice clearly when pilot is looking at instruments and when the warning speakers are direct line of sight to the mic.

A couple of panel mounted directional mics each aimed directly at where the pilot and FO is looking could be considered if boom mics cant be relied upon.
This will reduce background level relative to voice level. These mics and the ambient mic could be fitted with wind gags to eliminate the sound of air moving over the surface of the mic, so called "wind noise" that would otherwise greatly reduce the fidelity of the recording during a decompression or other event.

Cameras that show the crew mouths will help with deciphering what was spoken.
I guess that cvr use compression? Use of high rates of compression when there is lack of control over mic placement and background sound and when level control is "auto" is to be avoided. Compression trys to keep every hum and background noise (there is considerable background noise of air over the fuselage) at the expense of reducing amount of data to record the good stuff.

As with images, the less control of the subject the more beneficial it is to have a high fidelity equipment, in this case microphones and a recording strategy which allows far more detail to be extracted post event.

A camera looking into passenger cabin would be very useful to evaluate passenger response to emergencies including evacuation.
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Old 23rd Jan 2015, 22:09
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Yes I agree with you it seems most likely that the sharp turn was induced as a result of the stall. However the bus is supposed to be spin tolerant when stalled even in gusts or asymetric thrust. At least they have the FDR to analyse fully on this occasion.
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Old 23rd Jan 2015, 22:16
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Nose dive

I am not an A man, so hardly dare to comment on the rudder behaviour. However, many years ago, in the early days of the 757, a slow L HYD leak required the system to be switched off until required for the approach. For some reason all our aircraft required a great deal of rudder trim in the cruise (later corrected). Having such a leak and following the QRH, the result was an immediate 30 to 40 degree wing down. The aircraft, though, maintained straight and level (altitude but not wings!) flight with us hanging in our straps until the L HYD was quickly switched back on again. There was no immediate nose dive at all. This was due to a full rudder deflection. Mr B informed us later that the ratio of rudder deflection reduces with speed by 15 times due to the RUDDER RATIO which, of course, was switched off by selecting L HYD OFF.
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Old 23rd Jan 2015, 22:30
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One of the best techniques to keep an undesired FBW pitch up from bleeding off all your airspeed is to immediately drop a wing and convert pitch-up into turn. The little bus will let you get 67 degrees bank if you hold the stick over, right?
It may be that QZ8501 was doing that but got started too late and bled off too much speed and fell off onto the low wing in a stall.

For someone who flies the little 'bus:
How long do you think it would take to turn off two of the 3 computers if you were surprised by an undesired maneuver? I'm betting that it would be about 15 seconds from initial startle to Alternate Law-and that only if you were really on top of your game.
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Old 23rd Jan 2015, 23:02
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The equivalent deflection ratio exists on the airbus apparently, the AP can command +/- 3 degrees of rudder deflection at high speed to +/- 30 degrees at low speed. When actuated any deviation from the track is compensated with opposing elevator and aileron but AP aileron authority is limited and under the fault conditions the craft cannot maintain track, manual control is required.

At first it seems surprising that the AP can command a rudder deflection that would defeat lateral navigation, but if you consider normal operation would be to compensate for weathercock due to high winds not compensation for a software anomaly.
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Old 23rd Jan 2015, 23:44
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Human performance in stress / startle

The sad but interesting parts of the CVR / DFR data analysis will be the human response to some of the alarms.

If, as in , say Colgan style, or AF, the PF response to stall was NOT nose down, due to startle or whatever, does there need to be in the alarm aural sequence, the loud and repetitive message "pitch nose down" announced ?

Although it it obvious and basic, it is clear in recent years that it is not automatically done. And if there are already aural warnings with ground prox saying "pull up" (mind you not helpful if aircraft in stall), by which stage the a/c is 3 - 5 seconds from impact, why not a message such as above which would be helpful, while the a/c may still be at salvageable altitude.

Of course avoiding getting into the stall is preferable in the first place.

Just my 2c worth as a pax with frequent interaction of stress situations.
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Old 23rd Jan 2015, 23:54
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@FlightDream111 thanks for that link - also useful is the FAA upset recovery link at FAA TV: Airplane Upset Recovery, Part 2
mcloaked, you are welcome, hope it helps.

Its on tube as well : https://www.youtube.com/watch?v=gHf5XPO9wAA

The video shows what looks like a an A320 and cautions that air brake deployment may cause pitch up - is this true on the A 320?

Last edited by FlightDream111; 24th Jan 2015 at 00:18. Reason: you tube link
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Old 24th Jan 2015, 00:24
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aussiepax

I understand what you are getting at, but, believe it or not, if you are in a spin, in some planes, the nose is already down.

so, instead of saying: pitch nose down...it would be better if we all just PUSHED FORWARD ON THE STICK (control wheel or sidestick).

AND we should have learned this in our first lesson in a plane.

And Wolfgang Langweische, a great author of "stick and rudder" wrote about this over 70 years ago.

But you see, some smart ass somewhere said: oh, just ''relax back pressure"...and sometimes that is not enough.


So...here we are, 70 years AFTER
"STICK AND RUDDER" was published and we still don't get out of stalls right.

There is a good chance you will never have a problem...just ask your pilot : have you read, "stick and rudder"?
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Old 24th Jan 2015, 00:25
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Henra: "Doesn't fit this scenario.
At all.
Uncommanded rudder trim would cause a nose down dive and a sharp turn."

Well said, Henra. Kudos. The available evidence says this aircraft traded speed for altitude, until it stalled. Why? That's the question. The rudder can't make it climb like that. Stop the rudder nonsense. I'm just a humble private pilot, but this is obvious.
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Old 24th Jan 2015, 01:19
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Originally Posted by McWho
Yes I agree with you it seems most likely that the sharp turn was induced as a result of the stall. However the bus is supposed to be spin tolerant when stalled even in gusts or asymetric thrust. At least they have the FDR to analyse fully on this occasion.
If they have not tested the actual aircraft - it is only an assumption that the aircraft is 'spin tolerant' whatever that means. If you are actually at the point of stall and you have a compressor stall on one engine then that engine gives high drag and the other full thrust - this will stall the wing with the engine with compressor stall as it slows down relative to the other wing with full power. The aircraft starts to autorotate - a pilot without experience of entering a spin will attempt to lift the wing going down - precisely not what to do as it stalls that wing further. Then the out of spin g starts rapidly increasing on the flight deck. Spin recovery IMC on instruments takes practice which of course nobody has as 'you aren't supposed to be there'.
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Old 24th Jan 2015, 02:08
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Machinbird, One of the best techniques to keep an undesired FBW pitch up from bleeding off all your airspeed is to immediately drop a wing and convert pitch-up into turn. The little bus will let you get 67 degrees bank if you hold the stick over, right?
It works well at low altitude, at tropopause maybe only a F16 pilot would try it
In 1991 a German crew finally learned this technique in "the hard way"
http://www.youtube.com/watch?feature...ViilcDTyw#t=10

Last edited by _Phoenix; 24th Jan 2015 at 02:20.
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Old 24th Jan 2015, 02:31
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If they have not tested the actual aircraft - it is only an assumption that the aircraft is 'spin tolerant' whatever that means. If you are actually at the point of stall and you have a compressor stall on one engine then that engine gives high drag and the other full thrust - this will stall the wing with the engine with compressor stall as it slows down relative to the other wing with full power. The aircraft starts to autorotate -
Fanciful at best without actual numbers.

I believe there have been one or two events at altitude that prove this wrong
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Old 24th Jan 2015, 02:37
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Radar spiral/circle

Is there any possibility of narrowing by calculation the number of possible attitude scenarios regarding only the last spiral or circle on the radar track? Time involved is somewhat uncertain, but an estimate (or range of estimates) could be made of the number of returns which would help estimate the total time for the 360. That duration might be compared to the duration of a normal circle flown under control at zero descent rate which would also suggest an expected G rate relative to that turn. Or would adding the range of possible (or known) descent rates during the rotation include so many as to not be useful? Put another way, would radar turn indicated be equally possible in normal flight, stalled rotation, or intentional descending dive (I'm NOT suggesting the last...it is just part of the range possibilities.)
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Old 24th Jan 2015, 03:21
  #2439 (permalink)  
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A nice analysis of the debris field in relation to the radar plot

Source: Twitter


Last edited by training wheels; 24th Jan 2015 at 03:34.
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Old 24th Jan 2015, 04:01
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radome ?

can you say where is radome beaching in terms of this graphic ? I know it was 50 nm away
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