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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, 17:07
  #3041 (permalink)  
 
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RE Various posts

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. I don't recall any longer whether a single angle of descent was explored or whether the H stab was capable of various nose down settings allowing a variety of descent angles to be investigated. But the point was that a stable controlled descent in a fully stalled condition, well in excess of the perhaps 13 degree Wortman airfoil stall AOA of the 1-36 was achieved. And, importantly, was repeatedly recovered from.

There have been quite a few (not necessarily connected) posts now from pilots apparently familiar with the A320 suggesting that a combination of thrust moment, auto fly to G, mode of readouts, lack of pilot SS feedback, narrow speed margin, warning chaos, and possible rapidity of AOA change in relatively rare turbulence, not to mention pilot error (however small) and confusion over what the control system is thinking could ALL have contributed to two accidents where a stall all the way from altitude to impact occurred. There are more recently some hints (and counter opinion) that, once stalled, the A320 control system might actually be attempting to hold the plane in a stall.

A few posts have argued about whether the horizontal stab and elevator act to counter wing airfoil pitch moment, or to produce dynamic stability which is to a degree needlessly confusing because both moment forces and dynamic stability are involved. But those posts did not mention (and I don't think anyone has) running a relatively aft cg via fuel transfer to reduce drag by streamlining the Hstab/elevator, for fuel savings of course. I would appreciate some better detail from an A320 pilot on 1) whether and to what degree fuel transfer is used to supplement aerodynamic trim, 2) at what point in a flight is fuel transfer usually performed, 3) if fuel transfer is employed, is there an SOP for reversing that transfer in anticipation of encountering a storm line, and 4) wqhether the FDR would record fuel transfer events. Running on the ragged edge of an aft CG, even if inadvertant, of course would not be the best situation from which to begin an altercation with bad weather.

Jack of All, thanks for that post. How rapidly is the training you took being distributed through the entire pilot complement?
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Old 4th Feb 2015, 18:22
  #3042 (permalink)  
 
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Fuel transfer

I usually get modded out, even when I'm being constructive like now.
Someone will no doubt correct me, but I don't think the A320 has a wet tail.
So how to vary c.g?
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Old 4th Feb 2015, 19:12
  #3043 (permalink)  
 
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Silver

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.*
If you are refering to Turkish at AMS then the lack of recovery was more late recognition and inappropriate recovery techniques as I recall.
However the Bournemouth b737 incident shows quite clearly the effect toga has on the pitch attitude along with the fact the aircraft trimmed for slow speed. They recovered thankfully!
If your point is that maintaining max power makes the situation unrecoverable then yes, they did not recover until power was reduced and elevator authority regained.
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Old 4th Feb 2015, 19:17
  #3044 (permalink)  
 
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Jack:

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 surprised. I did mine on the 737 ten years ago. (But not enough retraining, I think.)

Why so late?
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Old 4th Feb 2015, 20:12
  #3045 (permalink)  
 
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Flexpwr:

To my knowledge, no commercial aircraft is ever directly "commanding" an attitude with either a stick or control column.
I'll see your confident gambit, and raise you ten....

The 737 in CWS mode does exactly that - it commands and maintains an attitude (always in pitch and sometimes in bank). And CWS is controlled by the control column. Which is why I thought the A320 must be doing the same type of thing.


Flexpwr:

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.
If you hold a constant 'g' with a decreasing speed the system will require an increasing pitch attitude to maintain 'g'. Conversely, holding an attitude will merely hold a constant attitude. The first design will get you into trouble before the second.

Any other questions?
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Old 4th Feb 2015, 20:30
  #3046 (permalink)  
 
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A320 fuel trim

A320 does not have an aft fuel trim tank. However to amend my earlier post, A320 CG does move with fuel consumption. So my question for Those Who Know remains somewhat the same: Would cg changes due to fuel burn in any way exacerbate the set of conditions already being discussed resulting in an unsustainable climb?

Quote “nice to know.. but in A320, CG always move backward with fuel consumption, irrespective of the tank..” at 13 Aug 2011 at:
fuel consumption and CG movement [Archive] - PPRuNe Forums

Other comments on A320 cg changes, Google:
trim changes due to a320 fuel consumption

Conflicting quote: “It's interesting to note that the performance chapter for the A320 bases all the figures on a MAC of 33%. Seems to me that if you start off with a MAC of34%, the fuel burn will cause the MAC to decrease during the flight towards a lower number, say about 30% depending on the length of the flight. This will keep the MAC close to the book value of 33%. Since the performance figures are based on 33%, wouldn't it make sense to load the airplane to reflect this value? Seems not many ops people, chief pilots etc pay much attention to this area.” 20 May 2013 at:
A320 CofG THS [Archive] - PPRuNe Forums
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Old 5th Feb 2015, 00:16
  #3047 (permalink)  
 
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Originally Posted by .Scott
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
Actually, the amount of stick you need to generate that rate of climb isn't a lot: as a rule of thumb for my TCAS responses (passed on down by an old hand) I use: 1° of pitch change results in about your Mach number in Rate of Climb: If you're doing .8 and you pull 1° of pitch, your ROC will be around 800ft/min. I haven't actually used 10° on a TCAS RA , but lesser changes indicate those numbers are pretty close. It's not difficult (and certainly not severe) to pull 10°: there's your 8000ft/min climb rate... for a short time at least.
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Old 5th Feb 2015, 00:19
  #3048 (permalink)  
 
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a lot of the discussions on the airbus fbw and just what is HAL capable of have questioned whether airbus actually do stall testing to garner data, does this post from way back throw any light on that

page 111 post2216

Quote:
Originally Posted by AM
The Concorde prototypes had a crew escape hatch
I'm not sure what your point is, but all the Airbus prototypes I've been on have had crew escape hatches. They would be used in case something went very badly during any of the many stall tests that were done
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Old 5th Feb 2015, 00:57
  #3049 (permalink)  
 
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Quoting Capn Bloggs
Actually, the amount of stick you need to generate that rate of climb isn't a lot: as a rule of thumb for my TCAS responses (passed on down by an old hand) I use: 1° of pitch change results in about your Mach number in Rate of Climb: If you're doing .8 and you pull 1° of pitch, your ROC will be around 800ft/min. I haven't actually used 10° on a TCAS RA , but lesser changes indicate those numbers are pretty close. It's not difficult (and certainly not severe) to pull 10°: there's your 8000ft/min climb rate... for a short time at least.
You're measuring the stick movement by the effect of pitch on the plane - rather than the position of the control surface.

Having never flown anything heavy, my assumption is that to reach an 800FPM climb (FACs not-withstanding), you would pull back on the stick far enough so that your target ROC was reached in perhaps 5 or 10 seconds. Then you would relax the stick a bit to hold that ROC.

However, if the control surface (the elevator) jammed in place you would find yourself at 800FPM in say 7 seconds, 1600FPM in 15 seconds, 2400FPM in 24 seconds, and only a your airspeed would keep you from completing an inside loop.

If that rate of climb isn't enough to build up to what was seen in RADAR, then perhaps the pilot was merely trying to maintain altitude in a sudden down-draft. He may have been very aggressive in trying to restore altitude and attempted to cause that 1 degree pitch up in much less than 7 seconds.

The point is that a control surface movement applied for 5 seconds can be very normal - but when jammed in place for tens of seconds can be very severe.

Also, there is no deicing provided on the tail of the A320.
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Old 5th Feb 2015, 01:30
  #3050 (permalink)  
 
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CG

On a swept wing, CG will always move back with fuel consumption if you deplete inside tanks first, which is preferential for wing loading

( assuming no other tanks, only wing tank )
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Old 5th Feb 2015, 07:55
  #3051 (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.
...
Actually it is for stability....modern jets are still aerodynamically stable..
The Stabilizer is for stability (hence the name), but it does not necessarily have to "push down the tail" for that. Only the momentum arms around the center of gravity, the wing area and the lift over AoA curve slope define whether an aircraft is stable or not, this does not determine the direction of the stabilizer force. To word it very simplistic, an aircraft is stable if the wing loading of the forward wing is greater (taking into account the sign) than that of the aft wing. If the wing loading of the aft wing is negative, this is the trivial case. But it might be also slightly positive (the stabilizer lifts the tail) while still maintaining stability. All modern gliders produce lift on the tail for speeds lower than best glide. However, to compensate for the pitching moment of a cambered airfoil on the main wing, the stabilizer always has to move the nose up (i.e. a Canard has to produce lift, a conventional tail has to push the tail down)
The highest stabilizer downforce required for modern transport aircraft is to compensate the extreme pitching moment of the main wing with full flaps. In cruise, modern aircraft do not produce significant downforce, some even produce slight lift. However, due to complexity trim tanks do disappear again, and we are now moving a bit away again from the idea of the stabilizer producing lift, as the drag penalty of the stabilizer downforce is neglectable in transonic cruise.
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Old 5th Feb 2015, 08:24
  #3052 (permalink)  
 
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Originally Posted by Volume
... a Canard has to produce lift, a conventional tail has to push the tail down
Thank you Volume for reinforcing that very point; the THS of a modern airliner has a negative camber, a point that I believe has been lost in the preceding discussion.
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Old 5th Feb 2015, 11:45
  #3053 (permalink)  
 
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Originally Posted by oldoberon View Post
a lot of the discussions on the airbus fbw and just what is HAL capable of have questioned whether airbus actually do stall testing to garner data, does this post from way back throw any light on that

page 111 post2216

Quote:
Originally Posted by AM
The Concorde prototypes had a crew escape hatch
I'm not sure what your point is, but all the Airbus prototypes I've been on have had crew escape hatches. They would be used in case something went very badly during any of the many stall tests that were done
If that is the case it seems somewhat dilatory to not provide the aircraft stall and post stall behavior information to the simulator designers. The sim behavior would be then be correct; and we are repeatedly told that it is not as there is 'no data' to base the behavior on.
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Old 5th Feb 2015, 12:14
  #3054 (permalink)  
 
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post 3061 - RetiredF4
And if the full forward stick does not lead to the desired reaction, feed in manual trim.
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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Old 5th Feb 2015, 13:11
  #3055 (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
  #3056 (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
  #3057 (permalink)  
 
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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
  #3058 (permalink)  
 
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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
  #3059 (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
  #3060 (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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