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FLYBY72
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Wed May 19, 2021 7:55 pm

zeke wrote:
FLYBY72 wrote:
Except it did happen in this event.


It did, the autopilot only disengages when the maximum authority is reached and it is exceeded, and when it is reached the control inputs go back from the maximum deflection to neutral, ie equivalate to a full opposite input while at the same time have idle thrust on one side and climb thrust on the other. For the pilots to save it they would have had to immediately recognize and understand what was happening, simultaneously lowered the nose, reduced thrust on both engines, and opposed the roll. No pilot is that good.

As far as the pilots were concerned the autopilot was doing as commanded, as they had commanded it to a right heading and level off at 11000 ft and they saw the right turn on the yoke and the aircraft leveling at 11000.


That situation is easily recoverable if the throttles are brought to idle. Once again. They purposefully left out when or if the crew ever brought the throttles to idle. Recover is only not possible if you leave the stuck throttle at full power.
 
Flaps
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Wed May 19, 2021 9:36 pm

zeke wrote:
FLYBY72 wrote:
Except it did happen in this event.


It did, the autopilot only disengages when the maximum authority is reached and it is exceeded, and when it is reached the control inputs go back from the maximum deflection to neutral, ie equivalate to a full opposite input while at the same time have idle thrust on one side and climb thrust on the other. For the pilots to save it they would have had to immediately recognize and understand what was happening, simultaneously lowered the nose, reduced thrust on both engines, and opposed the roll. No pilot is that good.

As far as the pilots were concerned the autopilot was doing as commanded, as they had commanded it to a right heading and level off at 11000 ft and they saw the right turn on the yoke and the aircraft leveling at 11000.


Which still leaves us with the crew failing to monitor the aircraft. It was not a sudden change of thrust. It was a steady though perhaps gradual change that at least one of the crew should have noticed during their scans (if they were doing so). There is no way that thrust differential should have gone unnoticed the way it did. Things never should have gotten to the point of autopilot disconnect in the first place. Were they that complacent or was something else going on that diverted their attention for more than just a few seconds?
 
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zeke
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Wed May 19, 2021 10:22 pm

orlandocfi wrote:
Isnt it amazing that there are thunderstorms every day around the globe and professional pilots manage to not fly into them?
Use of autopilot in extreme weather is actually not recommended as it can impose excessive loads on the aircraft structure. Does that have to be stated in the AFM?


I dont think your a pilot of an airliner to make those statements, especially the bit about "Use of autopilot in extreme weather is actually not recommended as it can impose excessive loads on the aircraft structure"

"Does that have to be stated in the AFM? " Absolutely has to be in the AFM/FCOM if it is a real limit.
“Don't be a show-off. Never be too proud to turn back. There are old pilots and bold pilots, but no old, bold pilots.” E. Hamilton Lee, 1949
 
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zeke
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Wed May 19, 2021 10:23 pm

FLYBY72 wrote:
Recover is only not possible if you leave the stuck throttle at full power.


Climb thrust is not "full power"
“Don't be a show-off. Never be too proud to turn back. There are old pilots and bold pilots, but no old, bold pilots.” E. Hamilton Lee, 1949
 
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zeke
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Wed May 19, 2021 10:26 pm

Flaps wrote:
Which still leaves us with the crew failing to monitor the aircraft. It was not a sudden change of thrust. It was a steady though perhaps gradual change that at least one of the crew should have noticed during their scans (if they were doing so). There is no way that thrust differential should have gone unnoticed the way it did. Things never should have gotten to the point of autopilot disconnect in the first place. Were they that complacent or was something else going on that diverted their attention for more than just a few seconds?


These older 737s have mechanical FCUs, it is normal to have a throttle split in the cockpit between sides when the same thrust is being produced.
“Don't be a show-off. Never be too proud to turn back. There are old pilots and bold pilots, but no old, bold pilots.” E. Hamilton Lee, 1949
 
orlandocfi
Posts: 130
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Wed May 19, 2021 11:23 pm

zeke wrote:
orlandocfi wrote:
Isnt it amazing that there are thunderstorms every day around the globe and professional pilots manage to not fly into them?
Use of autopilot in extreme weather is actually not recommended as it can impose excessive loads on the aircraft structure. Does that have to be stated in the AFM?


I dont think your a pilot of an airliner to make those statements, especially the bit about "Use of autopilot in extreme weather is actually not recommended as it can impose excessive loads on the aircraft structure"

"Does that have to be stated in the AFM? " Absolutely has to be in the AFM/FCOM if it is a real limit.


I fly the 737 in the US. We do not intentionally penetrate thunderstorms. We disconnect automation in turbulence that is severe or greater. SJ182 wouldn’t have crashed if they followed those guidelines. Nothing you have said in this thread changes that.
 
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zeke
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu May 20, 2021 1:31 am

orlandocfi wrote:
I fly the 737 in the US. We do not intentionally penetrate thunderstorms. We disconnect automation in turbulence that is severe or greater. SJ182 wouldn’t have crashed if they followed those guidelines. Nothing you have said in this thread changes that.


They didn’t enter a thunderstorm either, they got a heading to avoid. The crew between them had over 20 years experience on type operating in that area.
“Don't be a show-off. Never be too proud to turn back. There are old pilots and bold pilots, but no old, bold pilots.” E. Hamilton Lee, 1949
 
Flaps
Posts: 1722
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu May 20, 2021 9:05 am

zeke wrote:
Flaps wrote:
Which still leaves us with the crew failing to monitor the aircraft. It was not a sudden change of thrust. It was a steady though perhaps gradual change that at least one of the crew should have noticed during their scans (if they were doing so). There is no way that thrust differential should have gone unnoticed the way it did. Things never should have gotten to the point of autopilot disconnect in the first place. Were they that complacent or was something else going on that diverted their attention for more than just a few seconds?


These older 737s have mechanical FCUs, it is normal to have a throttle split in the cockpit between sides when the same thrust is being produced.

This is true but the difference in thrust indicated by the engine instruments should be glaringly apparent.....IF anyone was scanning them.
 
Sachmet
Posts: 20
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu May 20, 2021 12:44 pm

Flaps wrote:
zeke wrote:
FLYBY72 wrote:
Except it did happen in this event.


It did, the autopilot only disengages when the maximum authority is reached and it is exceeded, and when it is reached the control inputs go back from the maximum deflection to neutral, ie equivalate to a full opposite input while at the same time have idle thrust on one side and climb thrust on the other. For the pilots to save it they would have had to immediately recognize and understand what was happening, simultaneously lowered the nose, reduced thrust on both engines, and opposed the roll. No pilot is that good.

As far as the pilots were concerned the autopilot was doing as commanded, as they had commanded it to a right heading and level off at 11000 ft and they saw the right turn on the yoke and the aircraft leveling at 11000.


Which still leaves us with the crew failing to monitor the aircraft. It was not a sudden change of thrust. It was a steady though perhaps gradual change that at least one of the crew should have noticed during their scans (if they were doing so). There is no way that thrust differential should have gone unnoticed the way it did. Things never should have gotten to the point of autopilot disconnect in the first place. Were they that complacent or was something else going on that diverted their attention for more than just a few seconds?


It seems they where aware of the problem but somehow refrained from taking control back from the A/T system. (I could not verify the source of the statement below)
The flight data recorder recorded an error message from the automatic thrust control shortly after take-off. Instead of shutting down the system, according to Indonesian investigators, the pilots first tried to fix the problem.

this is from https://translate.google.com/translate? ... ch&pto=aue

I seen some link to an interim report on KNKT website but it didn't work (removed?) Its a bit confusing where they get this statement from but it does fit the general picture. As I wrote before it is quite possible that the pilots hesitated to take back the controls before they understood what exactly was happening. Over-reliance on automation can lead to this hesitation.
 
OldB747Driver
Posts: 108
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu May 20, 2021 1:43 pm

I see a number of statements here - late in the thread - that suggest both a lack of review of previous posts, but also a number of scenarios not really supported by the information we have available.

The latest publicly available reports seem to implicate the right thrust lever not responding to an A/T-commanded reduction of thrust resulting in a highly assymetric thrust condition. The role of weather, traffic and such seem to factor mainly as crew distractions rather than causal factors.

The A/P system (which operates in concert but with, but independently of, the A/T system) fuctioned in a manner consistent with its expected operation; it attempted to fly the aircraft along the commanded flight path until it reached its limits, at which point the software recognized it could not properly manage the flight path and disconnected. Unfortunately, if the A/P system has masked the malfunction of the A/T system as seems to have happened here, the disconnect immediately results in a rapid, chaotic departure from controlled flight.

When we watch a horror movie where the camera angle allows us to see the monster approaching an unaware victim, we do not blame the victim for not predicting that the monster would hide at THAT particular location, or did not figure out that "that particular noise" would result in a direct threat to their life. Similarly, we should be more aware of the human factors that are becoming more apparent with this accident.

Just like the horror-movie victim that could have avoided being killed by any number of different decisions, any flight crew can avoid the vast majority of these types of situations through strict discipline to procedure which, in turn, results in a high level of awareness and good decision-making. Our realization that this apparently did not happen, while instructive to rest of us, should be tempered with the reality that operating complex machines in highly dynamic situations on a routine basis results in "hours of boredom punctuated by moments of terror".
 
wjcandee
Posts: 10445
Joined: Mon Jun 05, 2000 12:50 am

Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu May 20, 2021 7:40 pm

Thanks for a rational, instructive, post, OldB747Driver!!
 
Sachmet
Posts: 20
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Wed Jun 02, 2021 8:33 pm

Not much of an update apart from saying they still somehow to much in the dark to come to any conclusion and having broken some test-equipment. But at least something:

https://translate.google.com/translate? ... &sandbox=1
 
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PixelFlight
Posts: 1033
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Sat Jun 12, 2021 12:15 pm

OldB747Driver wrote:
I see a number of statements here - late in the thread - that suggest both a lack of review of previous posts, but also a number of scenarios not really supported by the information we have available.

The latest publicly available reports seem to implicate the right thrust lever not responding to an A/T-commanded reduction of thrust resulting in a highly assymetric thrust condition. The role of weather, traffic and such seem to factor mainly as crew distractions rather than causal factors.

The A/P system (which operates in concert but with, but independently of, the A/T system) fuctioned in a manner consistent with its expected operation; it attempted to fly the aircraft along the commanded flight path until it reached its limits, at which point the software recognized it could not properly manage the flight path and disconnected. Unfortunately, if the A/P system has masked the malfunction of the A/T system as seems to have happened here, the disconnect immediately results in a rapid, chaotic departure from controlled flight.

When we watch a horror movie where the camera angle allows us to see the monster approaching an unaware victim, we do not blame the victim for not predicting that the monster would hide at THAT particular location, or did not figure out that "that particular noise" would result in a direct threat to their life. Similarly, we should be more aware of the human factors that are becoming more apparent with this accident.

Just like the horror-movie victim that could have avoided being killed by any number of different decisions, any flight crew can avoid the vast majority of these types of situations through strict discipline to procedure which, in turn, results in a high level of awareness and good decision-making. Our realization that this apparently did not happen, while instructive to rest of us, should be tempered with the reality that operating complex machines in highly dynamic situations on a routine basis results in "hours of boredom punctuated by moments of terror".


Thank you for your great post. :thumbsup:

From a safety point of view, I am wondering how much mitigation exists against the probable A/T malfunction scenario you describe. In this safety context the accident can be maybe be split in multiple parts like this:
1) Design decisions that can produce a fast and dangerous event in case of a single failure. The safety analysis of that failure and the resulting risk mitigation that was produced.
2) The information concerning that failure risk and the training of the appropriate mitigation.
3) The mitigation of the failure in flight before it produce the fast and dangerous event.
4) The mitigation of the failure in flight after if produce the fast and dangerous event.

While the point 1 and 2 can span a over long period of time, the pilots faced point 3 and 4 in a very limited time frame. My understanding so far is that point 3 time frame was a few minutes under near normal workload. The mitigation at that point was expected by scanning the available information and then implementing the right procedure. For some yet unknown reason that was sadly not what happened. The final report is expected to find what contributed to this. But humans are not 100% reliable, especially in case of rare event. This is why critical safety require multiple lines of mitigation. So what mitigation exists in that failure scenario is case the first mitigation did not success and that the malfunction finally produce a rare fast and dangerous event of the point 4? Was that possibility analysed at the design stage? Was an appropriate training defined and implemented to survive a such fast and dangerous event?
:stirthepot: 737-8 MAX: "For all speeds higher than 220 Kts and trim set at a value of 2.5 units, the difficulity level of turning the manual trim wheel was level A (trim wheel not movable)." :stirthepot:
 
bennett123
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Sat Jun 12, 2021 10:21 pm

Over the years, I have frequently heard the comment that the Autopilot kicks out if certain limits are exceeded, and basically says 'I can't handle this situation, you deal with it'.

Assuming I have this right, is it possible for the Autopilot to hold not just this red line, but an earlier amber one. At this point there would be an audible warning plus lights to say 'there is an issue which is within x% of the red line'. This would allow the pilots to take back control at a safer point, knowing that there was an issue.
 
ErichHartmann
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Tue Jul 13, 2021 12:56 pm

Is the audio of the CVR recoverable? Has it been downloaded? or what is the delay in finding out what was said in the cockpit?
 
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flyingturtle
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Tue Jul 13, 2021 7:36 pm

ErichHartmann wrote:
Is the audio of the CVR recoverable? Has it been downloaded? or what is the delay in finding out what was said in the cockpit?


It can easily take months until all sounds on the CVR are analyzed. For example, the boffins can analyze the noise of pressing buttons. Usually, they only release the CVR transcript when they have a solid interpretation of what the pilots said.
Reading accident reports is what calms me down
 
wjcandee
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Tue Jul 13, 2021 7:47 pm

flyingturtle wrote:
ErichHartmann wrote:
Is the audio of the CVR recoverable? Has it been downloaded? or what is the delay in finding out what was said in the cockpit?


It can easily take months until all sounds on the CVR are analyzed. For example, the boffins can analyze the noise of pressing buttons. Usually, they only release the CVR transcript when they have a solid interpretation of what the pilots said.


And to add to that, in certain regimes, like when the accident occurs in the US and the NTSB is the lead agency, the procedures of its "party system" means that representatives of all stakeholders ("parties") have a chance to listen to the recording and propose their own interpretation of what they hear. Sometimes, several parties will listen to it together with the Board investigators. Sometimes, they have proposed edits to the transcript, which are sometimes adopted. And this is a good system, even if it takes time. As evidence of that, I can point you to pretty-much every Youtube video where they try to put the ATC communications on the bottom of the screen. There's not one single video where I don't hear significant errors in the transcription. Now imagine you're listening to a CVR and trying to figure out the significance of not only every word, but every sound.

Yes, sometimes there can be too many cooks in a kitchen, but I think this is instead one of those circumstances where many heads are better than one, even if it takes time.

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