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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 3rd Feb 2015, 21:37
  #3001 (permalink)  
 
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Do bus pilots agree that given the amount of publicity hiven to these two accidents, that they should be able to identify and correct a high altitude stall?

Can further accidents of this type be prevented by vigilance alone?
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Old 3rd Feb 2015, 21:37
  #3002 (permalink)  
 
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@ physicus...

Thank you for that link on the Boeing/Airbus stall presentation it was very interesting.

I only wish we could have a similar presentation for T tail/aft mounted engine aircrafts (which I fly) to see the differences.

It was interesting to hear them say that under all stall condition a "lowering of the nose" was mandatory to reduce AOA, that you should not roll out and lower the nose of the aircraft at the same time (overstress the tail) but lower the nose first then roll out of the turn and finally not to increase the power but wait until establishes in the recovery prior to slowly increasing the power.

Finally it seems that Boeing with its 787 was moving toward Airbus' philosophy when it comes to FBW.
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Old 3rd Feb 2015, 22:28
  #3003 (permalink)  
 
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silverstrata (Bolding by me)

In normal law, an Airbus should never enter this state, but in alternate law it certainly can (as can Boeing twins). There is no reason why a stick pusher or a thrust reducer cannot be applied in these cases, where the aircraft is in alternate law. A thrust reduction at the point of stall, will lower the nose quite sharply (if the stick is neutral or forward of neutral) and make the exit of the stall relatively simple.
That statement of yours is imho misleading and does not reflect the correct procedure. A neutral stick in the bus commands a loadfactor of 1g, and would therfore force the aircraft in a decreasing speed environment due to power reduction in a higher AOA, the elevators and the THS may drive all the way nose up to achieve the commanded 1g. Same would happen with slight nose down input, as the increasing rate of descent in a stall would be felt by the sensors as less than 1 g, and the commanded g by a slight SS forward might be bigger, thus still the flight surfaces would be positioned for a nose up flight path. With such SS inputs the aircraft would be forced deeper into the stall and into high AOA. Bonin demonstrated how it would end. I'm not saying it might not drop the nose finally, but it might do it only in a very high stall state. And such a mistrimmed aircraft with the elevators and THS all nose up will be a definite handicap during recovery. It may even be the recipe for secondary stalls, as the increasing speed after a possible nosedrop could cause a pitchup again if not countered by manually trimming nose down and using amounts of SS forward to counter it.

So wy would you let this happen in the first place?

There is only one correct stick position as early in the stall as possible concerning the SS and especially in a flightpath stable aircraft like AB: Put the SS forward (and i would even say full forward) until the AOA is reduced to normal values and speed has reached flying airspeed.

We discussed that in the AF447 thread quite extensively, but this misjudgement of the effects of the flight computers under C* striving for the SS commanded g on the elevators and the THS trim from AB qualified crews is astonishing or even alarming.
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Old 3rd Feb 2015, 22:58
  #3004 (permalink)  
 
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1. Current simulator modeling DOES NOT give an accurate replication of jet airliner stalls, especially at high altitude. Both Airbus and Boeing say stalls in the a/c are more violent. They've recently agreed to a simulation model that works for n/b a/c (but not w/b's) that we might get to experience in a couple years.

2. You'll rarely see more than 5, or perhaps 6, degrees NU in an airliner above FL300. You need a v/s of greater than 2000-2,800 FPM to see pitch attitudes that exceed 5-6 degrees NU.
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Old 3rd Feb 2015, 23:40
  #3005 (permalink)  
 
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Stick Pushers and DP Davies

Davies did a long writeup on the certification requirement for stick pushers in T-tailed a/c.

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.

We are seeing high altitude stalls all the way to the ground and not just in Airbii - there's also at least one single engine turboprop I know of

To recover from a stall in an a/c certified as able to recover, you must first recognise it, then take appropriate corrective action.

Recognition becomes harder when the a/c settles into a steady state as with AF447 for which we do have data.

Certification requires the stall be recognisable. The nose drop has been superceded by aural warning, but as others have pointed out the human brain can shut down the auditory channel in high stress situations. I was in a simulator when the other pilot went inverted at 16,000' (white on black AH) and kept it there while I was shouting in his ear all the way to the ground.

What still bothers me about Brand A is that so far I have not heard of any test flights to determine stall behavior and recovery at any altitude.

Brand B seems to recover from high altitude stall events, but I have not come across any discussion that Brand B does stall test flights even though prevailing sentiment is that they likely do.
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Old 3rd Feb 2015, 23:56
  #3006 (permalink)  
 
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Brand B seems to recover from high altitude stall events
Would it, if the stab trim was wound fully back, the speed brought back to less than 100kts, with full power on and descending fast?
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Old 4th Feb 2015, 00:28
  #3007 (permalink)  
 
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Something more radical is required rather than the apparently easily ignore audio "stall", cricket, and warning lights.
If we are able to identify the stall from the FDR then the system can be programmed to know how to identify a stall upset. Why not program in an automated stall recovery once it has fallen like a rock 5'000. Allow the pilot to over ride but have "rescue mode" activate automatically. At that point the a/c is likely lost anyway. This could optimize the nose down and application of power to the best recovery.
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Old 4th Feb 2015, 00:45
  #3008 (permalink)  
 
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With reference to post #3021, superstrata,
A deep stall is any stall that cannot be remedied with elevators.
...and that character of a deep stall is almost exclusive to T-tail aircraft, but I prefer not to quibble over definitions, I'm more interested in characterizing and understanding stalls in which there remains some elevator authority and which, in transport aircraft, may be recoverable.
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Old 4th Feb 2015, 00:47
  #3009 (permalink)  
 
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No, instead of clamouring for more technology to fix the problems created by technology, train the drivers better. 30 minutes buzzing around on raw data (including wingovers, steep turns climb/slow/turn exercises), with 15 minutes of eyes-closed UA recoveries. This will reconnect pilots with the aeroplane so they will be better able to 1/not get into a handflying disaster aka AF447 (and perhaps 8501) and 2/be able to recognise that they are in a stalled state, regardless of how they actually got there, aka AF447, and recover.

And of course remove hand-flying auto trim!!
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Old 4th Feb 2015, 02:47
  #3010 (permalink)  
 
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One thing I dislike about [...] use of a verbal "STALL, STALL" (instead of a stick shaker) is that humans have a tendency to filter out aural inputs when concentrating or highly stressed. Meaning the STALL warning may not even be heard when it's most needed.
There is an interesting quote in this article from the pilot of Cathay Pacific 780 who after other severe trials had no control over engine thrust whilst landing and so came in extremely fast ... he said

“At that point, we started getting a lot of warnings going off in the cockpit, too. The cockpit started to become a very noisy place. All the systems are built into the airplane to warn you you’re approaching a dangerous area … the warnings were coming so thick and fast they were going over the top of each other.

“I had to put them all to one side, ignore them, and concentrate on what I thought was the most pressing issue, and that was to get the airplane on the ground as close as possible to the end of the runway.”
Which turned out safely for all involved.

Problem is, I'm not convinced that a stick shaker is much better - I can think of at least two [...] crashes where the pilot pulled back in response to an erroneous overspeed indication and stalled, then apparently dismissed the stick shaker as 'Mach buffet' due to the perceived overspeed.
A glider pilot much earlier in this thread mentioned that his stick would shake as an indication of a stall because the lack of clean airflow over the control surfaces. It was a direct mechanical link from the fluttering surfaces to the stick.

I know it's not a direct link in a transport. But does that mean that both edges of coffin corner provide the same cue to the pilot when different responses are required?

Given the choice between the two (and I realize never getting there is the best option) is exceeding the mach limit more recoverable than the stall at cruise altitude?
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Old 4th Feb 2015, 03:11
  #3011 (permalink)  
 
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...Same would happen with slight nose down input, as the increasing rate of descent in a stall would be felt by the sensors as less than 1 g, and the commanded g by a slight SS forward might be bigger, thus still the flight surfaces would be positioned for a nose up flight path. With such SS inputs the aircraft would be forced deeper into the stall and into high AOA. Bonin demonstrated...
RetiredF4,
You nailed it right in the sensitive spot
FBW software should ensure safe algorithm operation during entry into and recovery from a stall condition, THS trim function should be inhibited in the NU direction at a position that assures adequate stick/elevator control authority for stall recovery, even at full thrust. THS trim should be inhibited well before stall, based on AOA or speed margin above 1g-stall speed or esspecially if SW is online.
Brand B seems to recover from high altitude stall events
Would it, if the stab trim was wound fully back, the speed brought back to less than 100kts, with full power on and descending fast?
Capn Bloggs,
The force needed on the elevator would be large for THS NU, but it isn't any problem and there is the "feel" for need to trim forward.
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Old 4th Feb 2015, 03:25
  #3012 (permalink)  
 
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Originally Posted by Phoenix
The force needed on the elevator would be large for THS NU, but it isn't any problem
Isn't any problem? I doubt any fully-stalled aeroplane at slow speed and 40° AOA could be recovered using only full forward stick with a full back-trimmed stab.

and there is the "feel" for need to trim forward.
in the heat of the moment, when you never use the trim normally, I doubt very much whether you're going to remember to do it.
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Old 4th Feb 2015, 03:45
  #3013 (permalink)  
 
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Isn't any problem? I doubt any fully-stalled aeroplane at slow speed and 40° AOA could be recovered using only full forward stick with a full back-trimmed stab
40° AOA is quite extreme and not sustainable, but with THS at 25°-30° AOA, reduced thrust, the elevator at max ND would give a ND momentum

in the heat of the moment, when you never use the trim normally, I doubt very much whether you're going to remember to do it.
That's true for Perpignam, but in 4.5 minutes...
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Old 4th Feb 2015, 03:56
  #3014 (permalink)  
 
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@Capn Bloggs

It makes sense to have both. The tech needs to be constantly improved and refined. Always agree with more manual training and I would modify the certification for type to include a more significant manual flying quota. Otherwise there would be no incentive for it to be done.
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Old 4th Feb 2015, 05:58
  #3015 (permalink)  
 
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As a GA pilot who relies on stick and rudder skills. have been following this thread and feel quite concerned, even though obviously the results of the investigation are to be made.

I am concerned because there are perhaps some RPT Airline crews out there may have forgotten their basic training from the first 20 hours of their original flight training on:

1. Stall recovery - concerned that it appears that alarms about the Air Asia plane stalling were blaring for like 3 minutes - was the basic stall recovery of push the stick or column down/forward to reduce the AoA totally forgotten? including the use of the rudder to unstall a wing?

2. Taking care or avoiding flying through thunderstorms - when we all studied MET what were we taught? Thunderstorms have incredible energy that can tear an aircraft apart - concerned that tight time schedules and familiarity have bred contempt for these powerful weather phenomenon. As others have said, then Airlines crews decide to become Test Pilots it will eventually lead to disaster.

3. Over reliance on automation - too many systems designed to reduce workloads - what about actually knowing how to fly the plane without these? Today's aircraft are inherently more stable, less likely to stall and designed to be smoother in flight but it all can come apart if we let a computer pilot us rather than us piloting the plane.

Hope there are some good learning out of this tragic accident and the loss of life has not been in vein and contributes to improved safety in the RPT Airline industry.
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Old 4th Feb 2015, 06:49
  #3016 (permalink)  
 
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The accepted definition of the "deep stall" or "super stall" is that of Davies', which refers solely to the blanked T-tail designs.
The term "deep stall" (and the phenomena) already existed at least 3 decades before the first T-Tail was invented.
Basically what it means is stable flight in the region between the first Clmax (around 10° AoA, depending on the airfoil and configuration) and the second Clmax, which naturally occurs around 45° AOA for every airfoil. There is always a second "post stall" region of positive Cl over AoA slope, and if the horizontal stabilizer allows to get there, the aircraft can be flown stable in that region with lift and drag of similar magnitude, hence with flight path angles somewhere between 30 and 45 degrees. Depending on the overall design this condition can be so stable, that elevator efficiency is not enough to get out of that. The T-Tail is the most often occurring example for such configurations, but not the only one.
BTW, deep stall with T-Tails is not stable with the Tail in the wake of the wing, but with the Tail on the rear boundary of the wake. It is not so much because the elevator looses efficiency, it is because the flight condition is so extremely stable if any pitch up results in the tail leaving the wake and hence producing lift again and a nose down pitching moment, while pitching down results in the tail fully entering the wake and hence producing less lift and a nose up pitching moment. The Cm curve is so steep in that region, that shifting it up and down due to elevator deflection does not change the pitching moment significantly.
Canard configuration aircraft can even have stable deep stall around 230° AOA (inverted backwards...) as discovered during the SpeedCanard flight test...
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Old 4th Feb 2015, 06:58
  #3017 (permalink)  
 
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Quote:Phoenix
40° AOA is quite extreme and not sustainable, but with THS at 25°-30° AOA, reduced thrust, the elevator at max ND would give a ND movement.
But remember, under FBW C* implementation like AB in normal and alternate law the SS does not control the elevators directly. A SS neutral does not command an elevator at neutral position, it commands a loadfactor of 1g and the elevators and THS will be at whatever it takes to maintain or achieve this 1g. In a stalled condition like you describe with the THS all the way nose up the elevators would be nose up too.
The SS commands a loadfactor change, which the Flight computers will transfer into an elevator command with gains designed for comfort and in order not to exceed the loadfactor limitations. 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.
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Old 4th Feb 2015, 07:00
  #3018 (permalink)  
 
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Brand B seems to recover from high altitude stall events
Would it, if the stab trim was wound fully back, the speed brought back to less than 100kts, with full power on and descending fast?
Well, FWIW on at least some of Brand B's FBW aircraft stab trimming is inhibited below (approx) min manoeuvre speed.
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Old 4th Feb 2015, 07:04
  #3019 (permalink)  
 
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When a tail loses lift the nose pitches down because the horizontal stabilizer pushes the tail down for stability.
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Old 4th Feb 2015, 07:15
  #3020 (permalink)  
 
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bubbers44
When a tail loses lift the nose pitches down because the horizontal stabilizer pushes the tail down for stability.
True for an unstalled aircraft, different for an aircraft in a deep stall situation due to different reasons like shift of center of pressure, .......
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