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

Wed Feb 10, 2021 11:34 pm

Is it possible that we are now in an era where automated systems, designed to prevent a certain set of situations, or simply to assist the pilots, are now contributing to a whole new set of situations? IE, Over-reliance on said automation?

Time and time again we read that the pilots of this, that and the other crashed flight relied on the automated features and when faced with a situation outside the routine, they failed in basic airmanship.
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Wed Feb 10, 2021 11:40 pm

Blankbarcode wrote:
Wondering if an alert of "Approaching Limits" for the AP could be implemented, based on the rate it's approaching said limits, maybe maybe 5 seconds prior to A/P off? Additionally, maybe a slight audible indication the throttles are moving, something nondistracting but still noticeable? I'd think a slight clicking would be unobtrusive.

Of course, at a certain point you'll get a mountain of tiny adjustments that may not work well together, but thought I'd throw it out there.

Even the great fully FBW Airbus system does not have such an auotpilot disconnect pre-emptive warning system, so expecting that on a Boeing is way out there...
However, warning when the AP disconnects should be standard, so if not in the 737-500, maybe the FAA and EASA will demand same.
 
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 12:09 am

GalaxyFlyer wrote:
It’s not that hard, in any airplane to feel yaw. Yes, I’ve flown everything from Aeroncas to C-5s including Boeing and modern business jets. Sound and feel should quickly reveal a problem.

Never mind those engines, you feel yaw in a glider pretty easily. The yaw string taped to the canopy on pretty much every glider was invented by Wilbur Wright. I got pretty good at feeling yaw with my butt cheeks and applying a correction without referring to the yaw string.
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 12:10 am

Right rudder isn’t used to make turns, but would be used to correct thrust asymmetry
 
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 12:39 am

Cubsrule wrote:
I guess I don't really understand the point you are making. If we had an NG or Max or 748 that crashed due to some carryover technology, this would be a reasonable discussion. But the 735 isn't that. It's an aircraft on which 70s and 80s technology should be expected and planned and trained for.


The Sriwijaya Air fleet is comprised of 13 NGs and 5 classics. Perhaps the pilots were simply acclimated to flying a FADEC equipped plane.
 
OldB747Driver
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 12:43 am

VS11 wrote:
What was the heading before they requested change to 075 degrees? The left engine losing thrust started before the heading change request. If the new heading was to the right, and if I understood correctly that the autopilot wouldn’t control the rudder, then the PIC must have been applying right rudder as they were turning right. Is this not the case?

I don't believe that interpretation is quite right - to rephrase the likely scenario:

The implication is that the A/T clutch for the right engine disengaged (would not actually move the thrust lever to control thrust as designed).

The initial clearance was for much higher, but when they requested (and were approved) a new heading for weather avoidance, the new routing required a limit on the climb to 11,000'. Regardless of the A/T speed mode, a level-off would have required both engines to reduce thrust to prevent an overspeed condition as the A/P began to level out the aircraft as it approached 11,000' - except that only the left clutch seems to have been engaged (the right did not reduce thrust) and so during a fairly dynamic maneuver (25-30 degree right turn, leveling off, reducing thrust) the gradual increase in yaw may have either been unnoticed, or prossibly more likely, an oddity/sensation that didn't reflect the urgency of the dangerous condition they were rapidly approaching.

As far as rudder use is concerned, in swept-wing aircraft (and virtually all jets) the yaw damper performs the 'coordination' function, hence even if the pilot's feet are on the rudder pedals, they are not actively adding rudder input.
 
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 12:49 am

garpd wrote:
Is it possible that we are now in an era where automated systems, designed to prevent a certain set of situations, or simply to assist the pilots, are now contributing to a whole new set of situations? IE, Over-reliance on said automation?


This has been the case for a long time. Look up Vandenburg's videos from the late-90s, when the System Chief Pilot at American saw this problem and had Vandenburg do a whole course on it at the AA flight academy. One message: from time to time, turn off the automation and fly the airplane.

Unfortunately, the Schoolhouse is back to its old bean-counter-inspired silliness, and the stick and rudder have once again become the Emergency Flight Controls.

(For those who miss the tales of Fifi, the Electric Jet, you will recognize the references.)
 
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 1:20 am

FlyHossD wrote:
You mean other than the large split in the thrust lever postions?

Again, the large split in thrust position isn't a big warning in and of itself? The lever position may not directly correlate to a power setting, but a large split IS a warning.


It is normal with aircraft such as the 737-500 with hydromechanical fuel control units to have a throttle split.

Heinkel wrote:
Question: Does the 737 MAX have the same kind of auto pilot with limited capabilities like the 737 which crashed here?

Or did Boeing improve the AP on later models?


Yes same, however the engines are FADEC controlled.

VS11 wrote:
What was the heading before they requested change to 075 degrees? The left engine losing thrust started before the heading change request. If the new heading was to the right, and if I understood correctly that the autopilot wouldn’t control the rudder, then the PIC must have been applying right rudder as they were turning right. Is this not the case?


The aircraft never came around to a heading of 075.

No the pilots did not need to apply rudder, the yaw dampener would be trying to manage the yaw under direction of the autopilot.

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This image is my own work from FR24 data
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 1:37 am

wjcandee wrote:
garpd wrote:
Is it possible that we are now in an era where automated systems, designed to prevent a certain set of situations, or simply to assist the pilots, are now contributing to a whole new set of situations? IE, Over-reliance on said automation?


This has been the case for a long time. Look up Vandenburg's videos from the late-90s, when the System Chief Pilot at American saw this problem and had Vandenburg do a whole course on it at the AA flight academy. One message: from time to time, turn off the automation and fly the airplane.

Unfortunately, the Schoolhouse is back to its old bean-counter-inspired silliness, and the stick and rudder have once again become the Emergency Flight Controls.

(For those who miss the tales of Fifi, the Electric Jet, you will recognize the references.)


You are correct but I wouldn't throw all airline into the same basket. There's a big difference in talent between the likes of airlines such as UA/WN/OO/LH and Sriwijaya Air.
 
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 1:54 am

par13del wrote:
Blankbarcode wrote:
Wondering if an alert of "Approaching Limits" for the AP could be implemented, based on the rate it's approaching said limits, maybe maybe 5 seconds prior to A/P off? Additionally, maybe a slight audible indication the throttles are moving, something nondistracting but still noticeable? I'd think a slight clicking would be unobtrusive.

Of course, at a certain point you'll get a mountain of tiny adjustments that may not work well together, but thought I'd throw it out there.

Even the great fully FBW Airbus system does not have such an auotpilot disconnect pre-emptive warning system, so expecting that on a Boeing is way out there...
However, warning when the AP disconnects should be standard, so if not in the 737-500, maybe the FAA and EASA will demand same.


I'm pretty sure the autopilot disconnect warning was made standard after the Eastern Everglades crash. Pilots are supposed to be monitoring the aircraft systems. Especially during critical phases of flight. This idea of blaming the airplane for everything is going down a dangerous path. Either pilots are worth their salary or they're not. If they are just along for the ride and not responsible for the outcome of the flight then there is no justification for paying them a quarter of a million dollars a year.
 
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 3:17 am

Blankbarcode wrote:
Wondering if an alert of "Approaching Limits" for the AP could be implemented, based on the rate it's approaching said limits, maybe maybe 5 seconds prior to A/P off? Additionally, maybe a slight audible indication the throttles are moving, something nondistracting but still noticeable?

A good Upset Prevention and Recovery Training would include identification of behaviour that can lead to an upset, including seeing what the automation is doing prior to the thing giving up or making the aircraft enter an upset situation. You can put all the alarms and bells, but we've seen it before, we do not want an information overload.

FLYBY72 wrote:
Anyone consider that the right throttle was frozen in place and as the aircraft neared level off the AT commanded a thrust reduction and only 1 throttle (the left) was responding. So, to maintain speed it had to keep brining the ONE throttle back.

Definitely being considered. In the parliamentary hearing a few days before the release of the preliminary report, the crew had changed the mode from LNAV & VNAV to HDGSEL and VS. Unfortunately, not more is disclosed on this, but they were climbing at 4000fpm or so, and they could have (and appeared to have) reduced their climb rate prior to leveling out, and this could have resulted in the reduction in thrust demand (where if TL2 is stuck, TL1 would move).

The question is, how far did the throttle levers split? Did it exceed the normal limit acceptable by the autothrottle system, or? Unfortunately for us outside the investigation, wedon't have this information yet.

OldB747Driver wrote:
I'm saddened by the overall tone here about this accident - while it is crucial to determine the cause so we can improve training and/or mechanical devices we use in everyday flight operations all over the world, I only hope to lend some compassion to the conversation, on the sides of both the flight crew who may have had a lapse of judgement, and Boeing, who in current times has become a fashionable punching bag due to their poor [unrelated] design decisions in a similar yet really totally different model of B737.

I agree with this. Automation needs proper monitoring by the crew. Why the crew of this failed to conduct proper monitoring, needs to be looked so we can find out why.


OldB747Driver wrote:
The initial clearance was for much higher, but when they requested (and were approved) a new heading for weather avoidance, the new routing required a limit on the climb to 11,000'. Regardless of the A/T speed mode, a level-off would have required both engines to reduce thrust to prevent an overspeed condition as the A/P began to level out the aircraft as it approached 11,000' - except that only the left clutch seems to have been engaged (the right did not reduce thrust) and so during a fairly dynamic maneuver (25-30 degree right turn, leveling off, reducing thrust) the gradual increase in yaw may have either been unnoticed, or prossibly more likely, an oddity/sensation that didn't reflect the urgency of the dangerous condition they were rapidly approaching.

We can start guessing the operational distractions from instrument and automation monitoring by the crew in this case, but let me add to the quoted above.

Crew asked for heading, heading needs to be selected, and crosschecked. Then at around 9000, ATC asked for them to arrest their climb at 11000, again altitude needs to be selected and cross checked. At 10,000ft, PM would go switch off the landing lights, manipulate the fasten seatbelt signs as required, and check for cabin pressurization. Then they were told to continue to FL130, so again, altitude selection and cross checking, and then, Transition Level is at 11,000, so they set the altimeters to QNE and have to cross check.

This seems simple, but the chain of events could play a role in distracting the crew away from being able to notice something was wrong, and this is something the investigators would look at and that is why they want to get the CVR to understand the human factors behind it.
---
On the search for the CVR, unfortunately the specialist rescue/recovery divers are not there on site. The dive team from the firefighters are there, and there are concerns that they don't have the right experience required especially for long dives. I might call the aircraft insurers on this and get the usual team to at least be involved. The CVR is crucial in this accident.
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 3:34 am

TTailedTiger wrote:
wjcandee wrote:
garpd wrote:
Is it possible that we are now in an era where automated systems, designed to prevent a certain set of situations, or simply to assist the pilots, are now contributing to a whole new set of situations? IE, Over-reliance on said automation?


This has been the case for a long time. Look up Vandenburg's videos from the late-90s, when the System Chief Pilot at American saw this problem and had Vandenburg do a whole course on it at the AA flight academy. One message: from time to time, turn off the automation and fly the airplane.

Unfortunately, the Schoolhouse is back to its old bean-counter-inspired silliness, and the stick and rudder have once again become the Emergency Flight Controls.

(For those who miss the tales of Fifi, the Electric Jet, you will recognize the references.)


You are correct but I wouldn't throw all airline into the same basket. There's a big difference in talent between the likes of airlines such as UA/WN/OO/LH and Sriwijaya Air.


I was responding to the post that I quoted, talking about over-reliance on automation, and the fact that it's not a sudden new phenomenon.

Yes, there's a difference between training at the major US carriers and some foreign ones, but automation dependency and automation complacency are not new, and not limited to foreign carriers. When the airline basically-requires you to use automation for a whole range of stages of flight, and discourages hand-flying, it's an old issue that has become new again. Name a current major US carrier that encourages regular hand-flying as part of its training to combat automation complacency and dependency. I'm pretty sure you can't. (Maybe WN; I don't know about them.)

But this idea that we need even MORE automation because humans are fallible ignores the obvious point that automation is also fallible, and folks who don't actually fly enough to handle the plane when the automation gives up and hands it to them are a menace. Air France. Asiana. On and on. The reality is that all this automation is a very-helpful and useful tool, but it requires the humans to not only know how to fly the plane without the automation's help, it also requires them to understand how the automation works to a very-detailed degree, because in the end, the humans are the last line of defense and actually catch automation mistakes on a routine basis. The many who think that automation is a panacea have never flown an airplane.

This is a bit mystifying to me, and I would be very interested in the CVR, because many of the tasks that the crew had to do involved looking up, even briefly (cabin altitude check, landing lights, etc.), and presumably one's eyes would roll past the window. It's one thing to lose situational awareness when there are no outside clues (night, weather); it's more-surprising in daylight not in weather where one can validate the "instruments that have gone crazy" with what's outside the windscreen, particularly with at least one high-time pilot involved. Something had their heads very-much "inside", but not on the PFD ("EADI" on the Classics, I guess) or the EIS or the throttle quadrant, which is why I'm wondering in part about CRM.
 
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 10:46 am

wjcandee wrote:
But this idea that we need even MORE automation because humans are fallible ignores the obvious point that automation is also fallible, and folks who don't actually fly enough to handle the plane when the automation gives up and hands it to them are a menace. Air France. Asiana. On and on. The reality is that all this automation is a very-helpful and useful tool, but it requires the humans to not only know how to fly the plane without the automation's help, it also requires them to understand how the automation works to a very-detailed degree, because in the end, the humans are the last line of defense and actually catch automation mistakes on a routine basis. The many who think that automation is a panacea have never flown an airplane.



If you will have accidents and loss of lives with or without automation, the question then becomes one of risk. Flying has become more safe with more automation, right? So while the reliance on too much automation is not good, it has also meant a safer system as a whole. So do you allow more automation and work on finding the areas where there is a risk, knowing it would only happen when there has been an accident? Or do we return to a time where there were more accidents due to less automation knowing more pilots are needed that will have less experience in aircraft that will need more flying skills?
 
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 2:55 pm

zeke wrote:
Yes same, however the engines are FADEC controlled


Does this mean the FADEC handles the autothrottle (or maybe more correctly autothrust) duties rather than having a mechanical system physically grab hold of the actual throttle levers and move them in order to accomplish thrust changes, with the movement of the levers being just a generated effect there to tell the crew what the throttle positions would be for that thrust level?
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 3:24 pm

hivue wrote:
Does this mean the FADEC handles the autothrottle (or maybe more correctly autothrust) duties rather than having a mechanical system physically grab hold of the actual throttle levers and move them in order to accomplish thrust changes, with the movement of the levers being just a generated effect there to tell the crew what the throttle positions would be for that thrust level?


This is a photo of another 737-500 throttle quadrant in flight, notice the instruments have the same thrust setting however the throttle position to achieve that thrust has a large split.

Image

From https://avherald.com/h?article=40cba259/0012&opt=0

With FADEC to have the same thrust the throttles would be at the same position for the same thrust, with hydromechanical splits are common. The photo above is extreme IMHO, I would not accept that.
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 3:58 pm

zeke wrote:
hivue wrote:
Does this mean the FADEC handles the autothrottle (or maybe more correctly autothrust) duties rather than having a mechanical system physically grab hold of the actual throttle levers and move them in order to accomplish thrust changes, with the movement of the levers being just a generated effect there to tell the crew what the throttle positions would be for that thrust level?


This is a photo of another 737-500 throttle quadrant in flight, notice the instruments have the same thrust setting however the throttle position to achieve that thrust has a large split.

Image

From https://avherald.com/h?article=40cba259/0012&opt=0

With FADEC to have the same thrust the throttles would be at the same position for the same thrust, with hydromechanical splits are common. The photo above is extreme IMHO, I would not accept that.


Sorry, I wasn't clear. Since the NG and MAX are FADEC equipped, are AT duties handed to the FADEC in those airplanes or do the MAX and NG retain the same system as the classic where the throttles are mechanically moved by the AT to cause the necessary thrust changes?
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 4:21 pm

wjcandee wrote:
But this idea that we need even MORE automation because humans are fallible ignores the obvious point that automation is also fallible, and folks who don't actually fly enough to handle the plane when the automation gives up and hands it to them are a menace.

I think the notion that we need more automation is wrong. What we need is better automation. That means:
  • System failure assessment during development (FMECA, FHA,...)
  • Internal redundancy and automatic fault detection
  • Safe handover from automation to pilots
  • Realistic pilot performance assumptions in line with the mandated training
  • Improved HMI regarding automation status and status changes
  • Improved warning systems and failure handling

This has been a major part of aircraft development (for all manufacturers!) in the past 30 years. Digital systems offer easier methods for internal fault monitoring and redundancy. Multifunctional displays are better at conveying the system status than analog gauges. EICAS / ECAM can show notifications, warnings and checklists. Envelope protections offer an extra layer of safety when the autopilot is disconnected.

The less reliable a piece of automation (or a pilot) is, the more babysitting is required. This takes attention away from other important tasks and, over time, can lead to fatigue.
 
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 4:38 pm

Why can't we have better automation and better training? It doesn't have to be an either or.

If you look at the A320 vs 737NG crash stats - they are not materially different. The more automated 320 has not proven to be significantly better than the NG. Both designs could be improved and automated reducing workload and training on the automation so Pilots had more time to focus in training and in practice (yes hand flying from time to time in good weather) on what to do when the Automation fails and have the required hand flying skills and sharpness to make a difference.

That would have saved a lot of lives in the past 15 years.
 
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 5:07 pm

hivue wrote:
Sorry, I wasn't clear. Since the NG and MAX are FADEC equipped, are AT duties handed to the FADEC in those airplanes or do the MAX and NG retain the same system as the classic where the throttles are mechanically moved by the AT to cause the necessary thrust changes?


No FADEC is like the electronic control unit on a car that handles all the engine and emission functions. The autothrottle is more like the cruise control function. The cruise control talks to the ECU, like the autothrust talks to FADEC.
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 5:19 pm

zeke wrote:
hivue wrote:
Does this mean the FADEC handles the autothrottle (or maybe more correctly autothrust) duties rather than having a mechanical system physically grab hold of the actual throttle levers and move them in order to accomplish thrust changes, with the movement of the levers being just a generated effect there to tell the crew what the throttle positions would be for that thrust level?


This is a photo of another 737-500 throttle quadrant in flight, notice the instruments have the same thrust setting however the throttle position to achieve that thrust has a large split.

Image

From https://avherald.com/h?article=40cba259/0012&opt=0

With FADEC to have the same thrust the throttles would be at the same position for the same thrust, with hydromechanical splits are common. The photo above is extreme IMHO, I would not accept that.


That degree of split throttles shouldn’t have been airborne—needs to be fixed prior to flight. How much split is allowed in the AMM?
 
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 5:21 pm

morrisond wrote:
Why can't we have better automation and better training? It doesn't have to be an either or.

If you look at the A320 vs 737NG crash stats - they are not materially different. The more automated 320 has not proven to be significantly better than the NG. Both designs could be improved and automated reducing workload and training on the automation so Pilots had more time to focus in training and in practice (yes hand flying from time to time in good weather) on what to do when the Automation fails and have the required hand flying skills and sharpness to make a difference.

That would have saved a lot of lives in the past 15 years.


The hand flying needs to be in both VMC and IMC. Anybody can keep things upright on a clear day, it’s at night in cloud and turbulence that counts.
 
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CrewBunk
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 5:40 pm

With regard to the 2 axis autopilot, one is taught (or should be) of its limitations very early in simulator training. You have to constantly retrim the rudder during single engine work.

I used to irritate the hell out of our check pilots as every time I lost an engine, I’d disconnect the autopilot. At least that way I knew what the airplane was doing. They finally made me engage the autopilot for Cat II approaches as it was SOP. I soon learned of its limitations.

And that brings up another point, if you let the asymmetry get so bad that the autopilot is about to kick off, it does give you a very obvious warning. The yoke will be at its full deflection as the autopilot is trying to use roll to counteract yaw. You’d have to be blind to miss that. In fact, I used that yoke deflection as a way of seeing how well I was doing at keeping things trimmed.

But ... think about it. If the autopilot kicked off with full aileron deflection, on top of thrust asymmetry on top of not being aware of what’s going on .... you’d have quite a handful!

GalaxyFlyer wrote:
That degree of split throttles shouldn’t have been airborne—needs to be fixed prior to flight. How much split is allowed in the AMM?


I agree. In all my years flying the 737, I’ve never seen a thrust lever split like that. That would be very difficult to fly with the auto thrust off.

I think the worst I ever saw was about a half a knob of split.
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 5:44 pm

zippy wrote:
Cubsrule wrote:
I guess I don't really understand the point you are making. If we had an NG or Max or 748 that crashed due to some carryover technology, this would be a reasonable discussion. But the 735 isn't that. It's an aircraft on which 70s and 80s technology should be expected and planned and trained for.


The Sriwijaya Air fleet is comprised of 13 NGs and 5 classics. Perhaps the pilots were simply acclimated to flying a FADEC equipped plane.

Maybe FAA was right when they refused to allow WN to fly Classic, NG and MAX interchangeably.
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 5:57 pm

GalaxyFlyer wrote:
morrisond wrote:
Why can't we have better automation and better training? It doesn't have to be an either or.

If you look at the A320 vs 737NG crash stats - they are not materially different. The more automated 320 has not proven to be significantly better than the NG. Both designs could be improved and automated reducing workload and training on the automation so Pilots had more time to focus in training and in practice (yes hand flying from time to time in good weather) on what to do when the Automation fails and have the required hand flying skills and sharpness to make a difference.

That would have saved a lot of lives in the past 15 years.


The hand flying needs to be in both VMC and IMC. Anybody can keep things upright on a clear day, it’s at night in cloud and turbulence that counts.


I would agree - practise in IMC would be great - but given the apparent current level of airmanship - that may be best left in the SIM for a while until those skills are sharp enough to encourage Pilots to try that with real passengers as a normal course.
 
Cubsrule
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 6:02 pm

Revelation wrote:
zippy wrote:
Cubsrule wrote:
I guess I don't really understand the point you are making. If we had an NG or Max or 748 that crashed due to some carryover technology, this would be a reasonable discussion. But the 735 isn't that. It's an aircraft on which 70s and 80s technology should be expected and planned and trained for.


The Sriwijaya Air fleet is comprised of 13 NGs and 5 classics. Perhaps the pilots were simply acclimated to flying a FADEC equipped plane.

Maybe FAA was right when they refused to allow WN to fly Classic, NG and MAX interchangeably.


An interesting point. WN did a fair amount of work to standardize the cockpits across the Classic and NG fleets, like the use of the steam gauge "skin" on the NG displays. Has Sriwijaya done any of that sort of thing? It's not directly applicable to this accident of course (you can't put FADEC in a classic) but an intentional approach helps.
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airtechy
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 6:08 pm

Not jets but in all the twin pistons I've flown the mechanics working on them told me that the max mismatch was a half knob at normal cruise setting. The pics that Zeke posted show a mismatch that should have been caught in the power runup for takeoff and the plane should never have left the ground. Who knows what the engine mismatch would have been at max throttle! If two pilots were to miss that much obvious mismatch, there is an obvious training problem .. or worse. :shock:
 
Chemist
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 6:09 pm

Crew proficiency is an interesting problem. I can envision a graph of accident rate versus hand-flying time. No hand flying time increases risk. 100% hand-flying time also increases risk. There is probably some point on the curve where enough hand-flying time builds competency before there is enough statistical liklihood for mistakes to be made as often. So perhaps some defined hand-flying time target - say 5% of the time 10K feet and below - or something like that. So there's enough competency but not so much hand flying that the inevitable statistical human errors are too numerous. Just an idea that airlines might actually shoot for some optimal target of hand flying time - neither too much nor too little.
 
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 6:54 pm

Cubsrule wrote:
Revelation wrote:
zippy wrote:

The Sriwijaya Air fleet is comprised of 13 NGs and 5 classics. Perhaps the pilots were simply acclimated to flying a FADEC equipped plane.

Maybe FAA was right when they refused to allow WN to fly Classic, NG and MAX interchangeably.


An interesting point. WN did a fair amount of work to standardize the cockpits across the Classic and NG fleets, like the use of the steam gauge "skin" on the NG displays. Has Sriwijaya done any of that sort of thing? It's not directly applicable to this accident of course (you can't put FADEC in a classic) but an intentional approach helps.

It’s interesting but I’m not sure really relevant. The FAA had no issue with pilots at WN (and other US carriers) operating the Classics and NGs interchangeably. They just thought adding a third 737 variant into the mix was too much and ruled that pilots would only be allowed to fly two interchangeably, with WN deciding to dump the Classics rather than split the pilot group.
 
wjcandee
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 7:08 pm

zippy wrote:
The Sriwijaya Air fleet is comprised of 13 NGs and 5 classics. Perhaps the pilots were simply acclimated to flying a FADEC equipped plane.


In a FADEC-equipped plane, a throttle split would point to an issue; more so than with hydromechanical engine control.

In other words, if you're expecting the FMC/autothrottle to be commanding symmetric thrust, then on a FADEC-equipped plane, the back-driven handles should be in basically the identical place. It's only with hydromechanical controls that sometimes there's a split with symmetric thrust.
Last edited by wjcandee on Thu Feb 11, 2021 7:26 pm, edited 1 time in total.
 
Cubsrule
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 7:09 pm

Polot wrote:
Cubsrule wrote:
Revelation wrote:
Maybe FAA was right when they refused to allow WN to fly Classic, NG and MAX interchangeably.


An interesting point. WN did a fair amount of work to standardize the cockpits across the Classic and NG fleets, like the use of the steam gauge "skin" on the NG displays. Has Sriwijaya done any of that sort of thing? It's not directly applicable to this accident of course (you can't put FADEC in a classic) but an intentional approach helps.

It’s interesting but I’m not sure really relevant. The FAA had no issue with pilots at WN (and other US carriers) operating the Classics and NGs interchangeably. They just thought adding a third 737 variant into the mix was too much and ruled that pilots would only be allowed to fly two interchangeably, with WN deciding to dump the Classics rather than split the pilot group.


Did anyone besides WN have the same pilots operating Classics and NGs? I think AS and CO were the only two who had the types on property at the same time but maybe I'm missing one.
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Polot
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 7:16 pm

Cubsrule wrote:
Polot wrote:
Cubsrule wrote:

An interesting point. WN did a fair amount of work to standardize the cockpits across the Classic and NG fleets, like the use of the steam gauge "skin" on the NG displays. Has Sriwijaya done any of that sort of thing? It's not directly applicable to this accident of course (you can't put FADEC in a classic) but an intentional approach helps.

It’s interesting but I’m not sure really relevant. The FAA had no issue with pilots at WN (and other US carriers) operating the Classics and NGs interchangeably. They just thought adding a third 737 variant into the mix was too much and ruled that pilots would only be allowed to fly two interchangeably, with WN deciding to dump the Classics rather than split the pilot group.


Did anyone besides WN have the same pilots operating Classics and NGs? I think AS and CO were the only two who had the types on property at the same time but maybe I'm missing one.

DL did as well and probably some of those smaller charter carriers like Miami Air and whatnot.
 
Cubsrule
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 7:38 pm

Polot wrote:
Cubsrule wrote:
Polot wrote:
It’s interesting but I’m not sure really relevant. The FAA had no issue with pilots at WN (and other US carriers) operating the Classics and NGs interchangeably. They just thought adding a third 737 variant into the mix was too much and ruled that pilots would only be allowed to fly two interchangeably, with WN deciding to dump the Classics rather than split the pilot group.


Did anyone besides WN have the same pilots operating Classics and NGs? I think AS and CO were the only two who had the types on property at the same time but maybe I'm missing one.

DL did as well and probably some of those smaller charter carriers like Miami Air and whatnot.


I don't think DL had the same pilots flying Classics and 738s. I am certain that the ex-WA 733s were non-standard and that they did not share pilots between those and the 732s, which also overlapped. Obviously the 732s and 738s did not share pilots, although DL had both for close to a decade I think.
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Polot
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 8:20 pm

Cubsrule wrote:
Polot wrote:
Cubsrule wrote:

Did anyone besides WN have the same pilots operating Classics and NGs? I think AS and CO were the only two who had the types on property at the same time but maybe I'm missing one.

DL did as well and probably some of those smaller charter carriers like Miami Air and whatnot.


I don't think DL had the same pilots flying Classics and 738s. I am certain that the ex-WA 733s were non-standard and that they did not share pilots between those and the 732s, which also overlapped. Obviously the 732s and 738s did not share pilots, although DL had both for close to a decade I think.

I’m not 100% sure if the classics shared the pilots with the NGs or not at DL. They were not all exWA 733s, with about a 7 year overlap between the 733 and 738s.
 
Cubsrule
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 8:24 pm

Polot wrote:
Cubsrule wrote:
Polot wrote:
DL did as well and probably some of those smaller charter carriers like Miami Air and whatnot.


I don't think DL had the same pilots flying Classics and 738s. I am certain that the ex-WA 733s were non-standard and that they did not share pilots between those and the 732s, which also overlapped. Obviously the 732s and 738s did not share pilots, although DL had both for close to a decade I think.

I’m not 100% sure if the classics shared the pilots with the NGs or not at DL. They were not all exWA 733s, with about a 7 year overlap between the 733 and 738s.


You're correct on the timing I think because my memory is that the 732s stuck around a year or two longer than the 733s.
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hivue
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 8:48 pm

zeke wrote:
hivue wrote:
Sorry, I wasn't clear. Since the NG and MAX are FADEC equipped, are AT duties handed to the FADEC in those airplanes or do the MAX and NG retain the same system as the classic where the throttles are mechanically moved by the AT to cause the necessary thrust changes?


No FADEC is like the electronic control unit on a car that handles all the engine and emission functions. The autothrottle is more like the cruise control function. The cruise control talks to the ECU, like the autothrust talks to FADEC.


So the NG and MAX also have a hydraulic/mechanical AT system that clamps on to the throttle levers to actively move them in order to change thrust? Does Boeing do it that way on the 777 and 787? I believe AB uses the term "autothrust" rather than "autothrottle." How do they handle it?
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mxaxai
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 8:57 pm

hivue wrote:
I believe AB uses the term "autothrust" rather than "autothrottle." How do they handle it?

Airbus thrust levers don't move automatically at all. The AT just sends a message to the engines' FADEC, from one computer to another.
 
hivue
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 9:46 pm

mxaxai wrote:
hivue wrote:
I believe AB uses the term "autothrust" rather than "autothrottle." How do they handle it?

Airbus thrust levers don't move automatically at all. The AT just sends a message to the engines' FADEC, from one computer to another.


I realize AB thrust/throttle levers don't move.

It seems to me there are three ways to do the job: (1) A mechanical system linked to the AT literally grabs the throttle levers and moves them as the pilot would with his hand to change thrust; (2) the AT system (computer) sends signals to the FADECs to set the desired thrust and the throttle levers are left alone; and (3) the AT sends signals to the FADECs to set the desired thrust and the throttle levers are artificially moved so as to mimic what the AT has done.

I still am curious how Boeing does it on their FBW airplanes (777 and 787).
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CrewBunk
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Thu Feb 11, 2021 11:04 pm

mxaxai wrote:
Airbus thrust levers don't move automatically at all. The AT just sends a message to the engines' FADEC, from one computer to another.


From the A320 and later.

The A300’s and A310’s thrust levers move when autothrust commands. The A310 and A300-600 also have FADEC controlled engines.
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zeke
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Fri Feb 12, 2021 1:36 am

hivue wrote:
So the NG and MAX also have a hydraulic/mechanical AT system that clamps on to the throttle levers to actively move them in order to change thrust? Does Boeing do it that way on the 777 and 787? I believe AB uses the term "autothrust" rather than "autothrottle." How do they handle it?


The hydromechanical fuel control unit was is like a fancy carburettor, it sits on the engine scheduling fuel, FADEC also sits on the engine. The difference between FADEC and non FADEC is the throttle lever position on a FADEC engine will be the same both sides for the same thrust output. With hydromechanical fuel control units the throttle position does not necessarily correlate directly with the thrust output as it is a mechanical device, hence splits in throttle position is common, this is true for piston, turboprop, and jet aircraft that use a mechanical fuel scheduling..
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VirginFlyer
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Fri Feb 12, 2021 10:46 am

Cubsrule wrote:
Polot wrote:
Cubsrule wrote:

An interesting point. WN did a fair amount of work to standardize the cockpits across the Classic and NG fleets, like the use of the steam gauge "skin" on the NG displays. Has Sriwijaya done any of that sort of thing? It's not directly applicable to this accident of course (you can't put FADEC in a classic) but an intentional approach helps.

It’s interesting but I’m not sure really relevant. The FAA had no issue with pilots at WN (and other US carriers) operating the Classics and NGs interchangeably. They just thought adding a third 737 variant into the mix was too much and ruled that pilots would only be allowed to fly two interchangeably, with WN deciding to dump the Classics rather than split the pilot group.


Did anyone besides WN have the same pilots operating Classics and NGs? I think AS and CO were the only two who had the types on property at the same time but maybe I'm missing one.

I can think of several operators who had both Classics and NGs at the same time. Off the top of my head:

  • Qantas
  • Virgin Blue
  • Lauda
  • Ryanair
  • Aerolineas Argentinas

I’m sure there would be more. No idea if any of them had dedicated crews or one pool operating both.

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

Fri Feb 12, 2021 2:28 pm

zeke wrote:
FlyHossD wrote:
You mean other than the large split in the thrust lever postions?

Again, the large split in thrust position isn't a big warning in and of itself? The lever position may not directly correlate to a power setting, but a large split IS a warning.

It is normal with aircraft such as the 737-500 with hydromechanical fuel control units to have a throttle split.


In my approximately 14,000 hours in 737s, including this very same airframe, the largest split in thrust levers that I can recall was less than a full knob. Further, in the accident scenario, any split at take off and climb would not have matched the increasing split that lead to the upset.

Also, I’ll ask again - does your car need to have a Lane Departure Warning System to notice that you’ve drifted out of your lane?
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Cubsrule
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Fri Feb 12, 2021 2:32 pm

VirginFlyer wrote:
Cubsrule wrote:
Polot wrote:
It’s interesting but I’m not sure really relevant. The FAA had no issue with pilots at WN (and other US carriers) operating the Classics and NGs interchangeably. They just thought adding a third 737 variant into the mix was too much and ruled that pilots would only be allowed to fly two interchangeably, with WN deciding to dump the Classics rather than split the pilot group.


Did anyone besides WN have the same pilots operating Classics and NGs? I think AS and CO were the only two who had the types on property at the same time but maybe I'm missing one.

I can think of several operators who had both Classics and NGs at the same time. Off the top of my head:

  • Qantas
  • Virgin Blue
  • Lauda
  • Ryanair
  • Aerolineas Argentinas

I’m sure there would be more. No idea if any of them had dedicated crews or one pool operating both.

V/F


Yes, sorry - I was only listing US operators. You've listed a few more, and others include ET (albeit just a single 734) and LO.
Last edited by Cubsrule on Fri Feb 12, 2021 2:51 pm, edited 1 time in total.
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Exeiowa
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Fri Feb 12, 2021 2:49 pm

Can someone who understands the reading between the lines part of the report explain what was going on with the thrust asymmetry problem. As I know nothing about the mechanics of the system, what information the pilots are presented with and what information can we infer that it not spelled out. I feel like I am watching a scene through a peep hole where I cannot see everything at once but the rest of the people observing have a less obstructed view.
 
hamiltondaniel
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Fri Feb 12, 2021 3:20 pm

Exeiowa wrote:
Can someone who understands the reading between the lines part of the report explain what was going on with the thrust asymmetry problem. As I know nothing about the mechanics of the system, what information the pilots are presented with and what information can we infer that it not spelled out.


Essentially, it appears that the right autothrottle got "stuck," so the right engine remained at a higher thrust level. To keep on-speed, the autothrottle reduced thrust on the left engine disproportionately, creating the assymetry. The plane then wants to yaw to the left because the right engine is pushing harder than the left (it also wants to roll to the left, for aerodynamic reasons).

Up to a certain point, the autopilot was compensating for the leftward yaw and roll but eventually the assymetry became too large for the autopilot to counteract; the yaw damper on the 737 Classic (and the NG and MAX) has fairly limited authority over the rudder, so the autopilot had to overcompensate with excess roll, up to the limits. When the autopilot hit these limits, it switched off, and the pilots were not able to recover from the unusual attitude.

The pilots would have had several cues as to what was happening:

-Split throttles. The throttles are driven hydromechanically and some (small) split between position is normal; as discussed above, any gross difference is not normal and is a sign something is wrong.

-Different engine instrument levels. The N1 gauges in particular would have shown different numbers.

-PFD would have shown a leftward roll as the autopilot was driven out of limits.

-Inner-ear effects; the ear is generally pretty sensitive to slip/skid. Someone correct me if I'm wrong, but as the yaw damper was driven out of control authority, the plane would have been in a skid.

-Slip/skid indicator on the PFD would have shown the skid.

-Control wheel position. By the time the autopilot switched off, the control wheel would indicate significant RWD aileron.

-Autopilot disconnect warning when the autopilot disengaged.

Those would be the big ones.
 
pugman211
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Fri Feb 12, 2021 3:45 pm

If the above is true, then when the autopilot disconnected wouldn't the aircraft enter a sharp left turn? But the final seconds show a sharp right turn, which to me looks like pilot intervention, right?
 
Exeiowa
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Fri Feb 12, 2021 3:53 pm

Thank you for that explanation now the rest of the discussion is much clearer to me!
 
OldB747Driver
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Fri Feb 12, 2021 4:19 pm

pugman211 wrote:
If the above is true, then when the autopilot disconnected wouldn't the aircraft enter a sharp left turn? But the final seconds show a sharp right turn, which to me looks like pilot intervention, right?

I believe the information you're basing the right turn on was not complete, or based on available unfiltered or processed radar data. @mandala499 posted an accurate representation that illustrates the rapid left turn and the resulting steep descent and coincides rather precisely with the theory that the right thrust lever was at high power and the left at or near idle with the autopilot attempting to turn to a heading of 075 and level out at 11,000' until it was disconnected. It is difficult to convey how rapid/violent and confusing the left roll would have been to an unsuspecting crew.
 
Okie
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Fri Feb 12, 2021 4:38 pm

pugman211 wrote:
If the above is true, then when the autopilot disconnected wouldn't the aircraft enter a sharp left turn? But the final seconds show a sharp right turn, which to me looks like pilot intervention, right?


Once you roll over then the actions of the airplane appear reversed on radar because the radar is on the ground and it is then observing the top of the airframe instead of bottom.

Okie
 
OldB747Driver
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Fri Feb 12, 2021 5:02 pm

To follow up my previous post, with the bolded/italicized portion of the report's quote highlighted by me:
Preliminary Report wrote:
At 14:40:05 LT, the FDR data recorded the aircraft altitude was about 10,900 feet,which was the highest altitude recorded in the FDR before the aircraft started its descent. The AP system then disengaged at that point with a heading of 016°, the pitch angle was about 4.5° nose up, and the aircraft rolled to the left to more than 45°. The thrust lever position of the left engine continued decreasing while the right engine thrust lever remained. At 14:40:10 LT, the FDR data recorded the autothrottle (A/T) system disengaged and the pitch angle was more than 10° nose down. About 20 seconds later the FDR stopped recording. The last aircraft coordinate recorded was 5°57'56.21"S 106°34'24.86"E
 
airtechy
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Re: Sriwijaya Air 737-500 (SJ182 CGK-PNK) crashes shortly after takeoff

Fri Feb 12, 2021 8:26 pm

The engineer in me would sure like to see a block diagram of the autothrottle system to see how it is implemented. The thrust change required ( I assume based on airspeed error) has to be the split between the two engines, but how is that value acquired and how is it split between the two engines? You would think (?) that there would be a safeguard against such a large difference in commanded thrust from the two engines (such as maybe a look at the N1 gauges). :scratchchin:

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