Turkish airliner crashes at Schiphol
Join Date: Feb 2009
Location: New Mexico
Posts: 10
Likes: 0
Received 0 Likes
on
0 Posts
737only did you have the extreme trim?
So you found the pitch up managable if full throttle was applied at stick shaker. Did your autopilot run to extreme trim like that reached by Safta in his sim:
http://www.pprune.org/rumours-news/3...ml#post4770070
Do you think there should be a threshold of trim where the autopilot warns that g/a thrust would result in extreme pitchup? The autopilot would seem to have the independent informatiion necessary.
This plus the left alt dependency and second retard of the auto throttle would seem to be the lessons learned about the automation.
http://www.pprune.org/rumours-news/3...ml#post4770070
Do you think there should be a threshold of trim where the autopilot warns that g/a thrust would result in extreme pitchup? The autopilot would seem to have the independent informatiion necessary.
This plus the left alt dependency and second retard of the auto throttle would seem to be the lessons learned about the automation.
Join Date: Mar 2008
Location: USA
Posts: 2
Likes: 0
Received 0 Likes
on
0 Posts
When the system designers were doing the SSA, FHA, FMEA, etc... I wonder if they considered a RA failure able to lead to a Haz or Cat event? And regardless of the hazard classification, I wonder if they were assuming some sort of annunciation or other crew action as a mitigating factor.
Maybe Boeing will have Honeywell add dual RA to the AT, and add some RA fault accommodation?
Maybe Boeing will have Honeywell add dual RA to the AT, and add some RA fault accommodation?
Join Date: Jul 2003
Location: Canada
Posts: 445
Likes: 0
Received 0 Likes
on
0 Posts
Propulsion guy
Not having seen the relevant FHA, FMECA etc, I can only guess that the main mitigating factor would be that the crew would be monitoring the critical flight parameters during the approach in the event of an inadvertent power reduction.
Bobcat4
The statement I made wasn't regarding whether Boeing made a mistake or not with the design but that idle-bystander thought the system designer should be ashamed of himself. However with your quoted reference data, you should also be aware that Boeing do not make engines or hold their TC
Not having seen the relevant FHA, FMECA etc, I can only guess that the main mitigating factor would be that the crew would be monitoring the critical flight parameters during the approach in the event of an inadvertent power reduction.
Bobcat4
The statement I made wasn't regarding whether Boeing made a mistake or not with the design but that idle-bystander thought the system designer should be ashamed of himself. However with your quoted reference data, you should also be aware that Boeing do not make engines or hold their TC
Join Date: Jan 2008
Location: Germany
Posts: 11
Likes: 0
Received 0 Likes
on
0 Posts
Trim was no problem, because we reacted at the first onset of the stick shaker.
What we did not do, was waiting for 8 seconds after stick shaker activation to fly the recovery. The turkish crew did not wait either. Their problem was the throttle retarding again. 6 seconds idle is not survivable when flying stall avoidance.
Lessons apart from basic flying is:
-Building in RA comperator which gives you a RA disagree, however this would not been spotted by a crew which does no instrument scan
-Programming a new reversion mode if the speed is too low, even on the G/S, no matter what mode the A/T is in.
What we did not do, was waiting for 8 seconds after stick shaker activation to fly the recovery. The turkish crew did not wait either. Their problem was the throttle retarding again. 6 seconds idle is not survivable when flying stall avoidance.
Lessons apart from basic flying is:
-Building in RA comperator which gives you a RA disagree, however this would not been spotted by a crew which does no instrument scan
-Programming a new reversion mode if the speed is too low, even on the G/S, no matter what mode the A/T is in.
Join Date: Aug 2005
Location: Norway
Age: 56
Posts: 48
Likes: 0
Received 0 Likes
on
0 Posts
Nigd3,
Right! See you point. Still I doubt Rolls-Royce isn't in the same perfect shape as some thinks Boeing is... "Don't you think Rolls-Royce know how to make engines?", I can hear someone say.
Talking about high pitch close to stall... Some are suggesting that pilots were looking out to see the runway. Cloud at 700' so when coming through the cloud base they would be able to see the horizon. Or... ??? At the increasing nose-up pitch, maybe they didn't see it? Anyway, it should be possible to see of feel the pitch when they came down to 700', right?
Q: What do you (normally) detect first when getting close to a stall, the presumably awkward look of the visual references outside, or the stick shaker?
Edit: Or to put it another way: What comes first: The look or the feel?
The statement I made wasn't regarding whether Boeing made a mistake or not with the design but that idle-bystander thought the system designer should be ashamed of himself. However with your quoted reference data, you should also be aware that Boeing do not make engines or hold their TC
Right! See you point. Still I doubt Rolls-Royce isn't in the same perfect shape as some thinks Boeing is... "Don't you think Rolls-Royce know how to make engines?", I can hear someone say.Talking about high pitch close to stall... Some are suggesting that pilots were looking out to see the runway. Cloud at 700' so when coming through the cloud base they would be able to see the horizon. Or... ??? At the increasing nose-up pitch, maybe they didn't see it? Anyway, it should be possible to see of feel the pitch when they came down to 700', right?
Q: What do you (normally) detect first when getting close to a stall, the presumably awkward look of the visual references outside, or the stick shaker?
Edit: Or to put it another way: What comes first: The look or the feel?
Join Date: Apr 2005
Location: Australia
Posts: 1,414
Likes: 0
Received 0 Likes
on
0 Posts
As for the skills of flying, many of these come from practice and exposure to similar situations, which are the basis of experience
Join Date: Nov 1999
Posts: 8
Likes: 0
Received 0 Likes
on
0 Posts
Are systems designers not permitted to assume a level of basic ability from pilots? Isn't that what we're paid for?
I'm afraid I'm in the exCargoClown camp at the moment - "There is something very wrong with all of this"
I'm afraid I'm in the exCargoClown camp at the moment - "There is something very wrong with all of this"
Join Date: Feb 2009
Location: New Mexico
Posts: 10
Likes: 0
Received 0 Likes
on
0 Posts
Is Turkey now ready for pilots to share some fault?
2-) pilots paniced from the 1st reason
Join Date: Nov 2007
Location: Northampton
Posts: 5
Likes: 0
Received 0 Likes
on
0 Posts
But newly graduated CPL pilots such as the multi-crew pilot licence first officers with less than 40 hours in a light aircraft are now second in command of some heavy iron. No "experience" necessary.
Anyway the MPL is covered in many different threads.
bob cat4
Yes your facts are right. However the critique of the laymen in this thread is that they know what and where the mistake was made.
I have learned that everything that man has made will break. Thus as a system safety specialist one adds mitigating factors to the analysis of how often (it malfunctions) and how.
Yes in this accident something has gone wrong in these assumptions. Without more data I don't know what to fix yet.
I sense that the great majority of experience on this board is on the same page. So I tend to gloss over shoot from the hip comments about "bad design"
History has proven Boeing (and others) makes mistakes like bad design. ........
So why should we believe that "This time they've got it right!" ?
And life on this thread has taught me to add: The above is not directly related to this accident, but as a comment to those who flame laymen for insinuate aircraft manufactures may make a mistake or two...
So why should we believe that "This time they've got it right!" ?
And life on this thread has taught me to add: The above is not directly related to this accident, but as a comment to those who flame laymen for insinuate aircraft manufactures may make a mistake or two...
I have learned that everything that man has made will break. Thus as a system safety specialist one adds mitigating factors to the analysis of how often (it malfunctions) and how.
Yes in this accident something has gone wrong in these assumptions. Without more data I don't know what to fix yet.
I sense that the great majority of experience on this board is on the same page. So I tend to gloss over shoot from the hip comments about "bad design"
Join Date: Nov 2006
Location: SoCalif
Posts: 896
Likes: 0
Received 0 Likes
on
0 Posts
Comparator Warning Monitors, which included Rad Alt, have been around since the 707 and DC-8. Does the 737 NG really lack a RadAlt comparator warning, as stated repeatedly in this thread?
GB
GB
Join Date: Jan 2008
Location: Overtheristan
Age: 54
Posts: 23
Likes: 0
Received 0 Likes
on
0 Posts
new food for speculation?
Hello all,
Some more things to think about......?
Stall Identification
Stall identification and control is enhanced by the yaw damper, the Elevator Feel
Shift (EFS) module and the speed trim system. These three systems work together
to help the pilot identify and prevent further movement into a stall condition.
During high AOA operations, the SMYD reduces yaw damper commanded rudder
movement.
The EFS module increases hydraulic system A pressure to the elevator feel and
centering unit during a stall. This increases forward control column force to
approximately four times normal feel pressure. The EFS module is armed
whenever an inhibit condition is not present. Inhibit conditions are: on the ground,
radio altitude less than 100 feet and autopilot engaged. However, if EFS is active
when descending through 100 feet RA, it remains active until AOA is reduced
below approximately stickshaker threshold. There are no flight deck indications
that the system is properly armed or activated.
As airspeed decreases towards stall speed, the speed trim system trims the
stabilizer nose down and enables trim above stickshaker AOA. With this trim
schedule the pilot must pull more aft column to stall the airplane. With the column
aft, the amount of column force increase with the onset of EFS module is more
pronounced.
Did the failed RA trigger an inhibit condition? I am speculating here, but I would not be surprised.
Rgds
emjanssen
Some more things to think about......?
Stall Identification
Stall identification and control is enhanced by the yaw damper, the Elevator Feel
Shift (EFS) module and the speed trim system. These three systems work together
to help the pilot identify and prevent further movement into a stall condition.
During high AOA operations, the SMYD reduces yaw damper commanded rudder
movement.
The EFS module increases hydraulic system A pressure to the elevator feel and
centering unit during a stall. This increases forward control column force to
approximately four times normal feel pressure. The EFS module is armed
whenever an inhibit condition is not present. Inhibit conditions are: on the ground,
radio altitude less than 100 feet and autopilot engaged. However, if EFS is active
when descending through 100 feet RA, it remains active until AOA is reduced
below approximately stickshaker threshold. There are no flight deck indications
that the system is properly armed or activated.
As airspeed decreases towards stall speed, the speed trim system trims the
stabilizer nose down and enables trim above stickshaker AOA. With this trim
schedule the pilot must pull more aft column to stall the airplane. With the column
aft, the amount of column force increase with the onset of EFS module is more
pronounced.
Did the failed RA trigger an inhibit condition? I am speculating here, but I would not be surprised.
Rgds
emjanssen
Join Date: Sep 2000
Location: England
Posts: 303
Likes: 0
Received 0 Likes
on
0 Posts
That Deadly Pitch-up Trim State Explanation was established at the beginning
Safta said at post 1630 http://www.pprune.org/rumours-news/3...ml#post4770070
Today we simulated the Turkish scenario in a B733 simulator. At 1800 feet AGL and established on the ILS, we retarded the throttles to idle, simulating what the Turkish B738 autopilot did. The aircraft started trimming slowly at first, and then more and more rapidly to maintain the glide slope. We allowed the stick shaker to activate and after around 8 seconds of stick shaker we applied full thrust and attempted a recovery without reconfiguring. With the control yoke pushed as far forward as it could go, the aircraft started to accelerate and a climb was initiated and it appeared that we were recovering. Note that this is with the yoke pushed forward against the forward stop. Then, all of a sudden, the aircraft entered a deep stall as the rudder lost effectiveness and the aircraft forward speed rapidly bled off and we entered a 6000 ft/min plus rate of descent until impacting the ground in an apparent tail low attitude.
The reason for our not recovering was due to the extreme amount of trim the autopilot had applied while attempting to maintain the glide slope. The only way that we could have recovered would have been to apply extensive nose down trim during the initial recovery.
We performed this exercise twice and both times produced the same result. We firmly believe that this is what was the cause of the Turkish crash.
Today we simulated the Turkish scenario in a B733 simulator. At 1800 feet AGL and established on the ILS, we retarded the throttles to idle, simulating what the Turkish B738 autopilot did. The aircraft started trimming slowly at first, and then more and more rapidly to maintain the glide slope. We allowed the stick shaker to activate and after around 8 seconds of stick shaker we applied full thrust and attempted a recovery without reconfiguring. With the control yoke pushed as far forward as it could go, the aircraft started to accelerate and a climb was initiated and it appeared that we were recovering. Note that this is with the yoke pushed forward against the forward stop. Then, all of a sudden, the aircraft entered a deep stall as the rudder lost effectiveness and the aircraft forward speed rapidly bled off and we entered a 6000 ft/min plus rate of descent until impacting the ground in an apparent tail low attitude.
The reason for our not recovering was due to the extreme amount of trim the autopilot had applied while attempting to maintain the glide slope. The only way that we could have recovered would have been to apply extensive nose down trim during the initial recovery.
We performed this exercise twice and both times produced the same result. We firmly believe that this is what was the cause of the Turkish crash.
headed "Think G-stall"
In the 15 seconds between 09:25:23 and 09:25:38 UTC, at around 350 to 400ft agl, soon after breaking cloud, and with Auto-throttle not obliging with any drag-opposing thrust, the aircraft stick-shaker would have cooked off and the surprised pilot would have disconnected the autopilot and selected an SOP max-power, yet immediately encountered the fierce zooming effect of low-speed max power pitchup. However combined with that nose-up couple, at autopilot disconnect, additionally and fatally, courtesy of the insidious effect of auto-trim, he'd have also unexpectedly liberated a yoke-full of max elevator backtrim and nose-up stabilizer. That he would have been then pushing and fighting that powerful nose-up pitch couple would be without question.
In the 15 seconds between 09:25:23 and 09:25:38 UTC, at around 350 to 400ft agl, soon after breaking cloud, and with Auto-throttle not obliging with any drag-opposing thrust, the aircraft stick-shaker would have cooked off and the surprised pilot would have disconnected the autopilot and selected an SOP max-power, yet immediately encountered the fierce zooming effect of low-speed max power pitchup. However combined with that nose-up couple, at autopilot disconnect, additionally and fatally, courtesy of the insidious effect of auto-trim, he'd have also unexpectedly liberated a yoke-full of max elevator backtrim and nose-up stabilizer. That he would have been then pushing and fighting that powerful nose-up pitch couple would be without question.
and 699
and later repeated/expanded upon by UNCTUOUS at post 1385
Join Date: Aug 2005
Location: Norway
Age: 56
Posts: 48
Likes: 0
Received 0 Likes
on
0 Posts
lomapaseo
Yes, I agree. We should not rule out technical flaws, but to fix them is far easier said that done. I have to admit I tried (as a layman) and jumped to this conclusion: "If auto-retard is not needed during a single channel approach, get rid of it."
Well, it turned out to be needed. And I see the need for it. Pilots want under-speed protection during approach, right until flare. Then they want over-speed protection, hence the only "logical" thing to do is retard. The definition of "flare" is a given altitude over ground so RA is a perfect choice (if not the only choice). One could argue that a single RA in this situation is perilous, but a single channel approach is an aid, not a auto-land feature. Auto throttle in this configuration is not supposed to be fail safe. I guess pilots know that, and keep scanning their primary instruments.
The real danger about automation is that it is too damn perfect. If you fly 1000 single channel approaches and everything is normal, speed, attitude, altitude etc... Would you really be that careful the 1001st time scanning your instruments? As a PPL-rookie I've learned that the safest pilot is the rookie (with some but still very little experience) trying to do everything by the book. When you become a veteran errors come more easily.
It's like trying to quit smoking. The first months you are very aware of being a non-smoker. Then you have quit, and are done with that... Just one smoke doesn't hurt? Well it does! Been there, done that! (And I still smoke)
Yes your facts are right. However the critique of the laymen in this thread is that they know what and where the mistake was made.
Well, it turned out to be needed. And I see the need for it. Pilots want under-speed protection during approach, right until flare. Then they want over-speed protection, hence the only "logical" thing to do is retard. The definition of "flare" is a given altitude over ground so RA is a perfect choice (if not the only choice). One could argue that a single RA in this situation is perilous, but a single channel approach is an aid, not a auto-land feature. Auto throttle in this configuration is not supposed to be fail safe. I guess pilots know that, and keep scanning their primary instruments.
The real danger about automation is that it is too damn perfect. If you fly 1000 single channel approaches and everything is normal, speed, attitude, altitude etc... Would you really be that careful the 1001st time scanning your instruments? As a PPL-rookie I've learned that the safest pilot is the rookie (with some but still very little experience) trying to do everything by the book. When you become a veteran errors come more easily.
It's like trying to quit smoking. The first months you are very aware of being a non-smoker. Then you have quit, and are done with that... Just one smoke doesn't hurt? Well it does! Been there, done that! (And I still smoke)
Last edited by bobcat4; 13th Mar 2009 at 17:28. Reason: typos
Join Date: Jan 2008
Location: Overtheristan
Age: 54
Posts: 23
Likes: 0
Received 0 Likes
on
0 Posts
@ theshadow
I suggest you read my posting better.
It's not about standard trim behavior.
I don't think the "100 ft inhibit" of the EFS is discussed on this forum. Or did I miss something?
Rgds
emjanssen
I suggest you read my posting better.
It's not about standard trim behavior.
I don't think the "100 ft inhibit" of the EFS is discussed on this forum. Or did I miss something?
Rgds
emjanssen
Join Date: Feb 2009
Location: New Mexico
Posts: 10
Likes: 0
Received 0 Likes
on
0 Posts
Re: That Deadly Pitch-up Trim State Explanation was established at the beginning
The Shadow,
Thanx for the reminder links. It is too hard to find them all, but there were some posts that argued that the stick shaker at 500ft was recoverable. So it may not really be "eastablished". Here is one:
http://www.pprune.org/rumours-news/3...ml#post4768223
I think there were a couple verifying recoveries in sim.
How unrecoverable was the trim and pitch up on G/A thrust versus the second uncommanded AT retard which there seems to be general agreement sealed their fate.
Thanx for the reminder links. It is too hard to find them all, but there were some posts that argued that the stick shaker at 500ft was recoverable. So it may not really be "eastablished". Here is one:
http://www.pprune.org/rumours-news/3...ml#post4768223
I think there were a couple verifying recoveries in sim.
How unrecoverable was the trim and pitch up on G/A thrust versus the second uncommanded AT retard which there seems to be general agreement sealed their fate.
Join Date: Jan 2008
Location: US
Posts: 251
Likes: 0
Received 0 Likes
on
0 Posts
bobcat4
Well, it's debatable whether the under-speed/over-speed protection available is worth the risk of a single malfunctioning RA surreptitiously placing A/T in the RETARD mode at 2000' and/or commanding idle thrust after manually selecting max thrust during a stall recovery attempt.
Note: you don't get Min. Speed Reversion with a coupled approach on the G/S. Unclear if MSR returns once the pilot de-selects the autopilot, I expect it does.
Pilots want under-speed protection during approach, right until flare. Then they want over-speed protection, hence the only "logical" thing to do is retard.
Note: you don't get Min. Speed Reversion with a coupled approach on the G/S. Unclear if MSR returns once the pilot de-selects the autopilot, I expect it does.
Last edited by MU3001A; 13th Mar 2009 at 18:52.
Join Date: Mar 2009
Location: S23W046
Age: 73
Posts: 57
Likes: 0
Received 0 Likes
on
0 Posts
Calling for changes in design
In many posts here you would call for changes in design of A/P A/T systems. I appreciate any positive changes increasing safety, but strongly belive that we as humans hardly ever will be able to create a machine or software that is 100%. You change the design on the 737 and looking at the next accident we will be posting in another thread about aviate, navi..........
What I want to say is, if we let the chain of events carry on without stopping it, we will put our lives and the A/C at risk. IMHO we as pilots are paid to cover system abnormals, whatever they are. To execute that task we should have system knowledge, SOP, CRM and hopefully handflying skills on our side. Now, if you ignore all indications that the system provides is like driving down a mountain road with a 100 mph and just before o sharp bend turning around to fetch a map from the backseat with both hands.
Anyone out there who could explain how that particular crew would have detected a windshear or how they would have done a recovery from a faulty airspeed indication?
I don't recall all the indicator or system faults I have encountered in the last 40 years, as I am pretty sure the majority of pilots in this forum, and in some situations hit the panic buttons: the one on the yoke and the one at the side of the throttles.
What I want to say is, if we let the chain of events carry on without stopping it, we will put our lives and the A/C at risk. IMHO we as pilots are paid to cover system abnormals, whatever they are. To execute that task we should have system knowledge, SOP, CRM and hopefully handflying skills on our side. Now, if you ignore all indications that the system provides is like driving down a mountain road with a 100 mph and just before o sharp bend turning around to fetch a map from the backseat with both hands.
Anyone out there who could explain how that particular crew would have detected a windshear or how they would have done a recovery from a faulty airspeed indication?
I don't recall all the indicator or system faults I have encountered in the last 40 years, as I am pretty sure the majority of pilots in this forum, and in some situations hit the panic buttons: the one on the yoke and the one at the side of the throttles.