737-500 missing in Indonesia
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fdr
interesting
“Our environment is stochastic, with a bucket of inputs and factors that impact every moment of our interface with the job at hand. from noise of heavy rain impact, accelerations at the seat from turbulence, ATC interactions, cockpit coordination, cabin needs, flight path management and systems.”
Quite true. But I always thought that that was the job.
I have 20,000 hours flying Boeing aircraft with most being routine interspersed with moments , uuhm , not routine.
In the not routine moments my crew has responded as trained. Professionally and effectively.
Maybe I have just been lucky.
I have also operated in Indonesia.
It wont be the aircraft.
interesting
“Our environment is stochastic, with a bucket of inputs and factors that impact every moment of our interface with the job at hand. from noise of heavy rain impact, accelerations at the seat from turbulence, ATC interactions, cockpit coordination, cabin needs, flight path management and systems.”
Quite true. But I always thought that that was the job.
I have 20,000 hours flying Boeing aircraft with most being routine interspersed with moments , uuhm , not routine.
In the not routine moments my crew has responded as trained. Professionally and effectively.
Maybe I have just been lucky.
I have also operated in Indonesia.
It wont be the aircraft.
Educated guess - the speculation of a thrust lever clutch failure will be correct. One engine throttle failed to move in response to the autothrottle command at level off (bad clutch, or high downstream forces due to a seized pulley or kinked push-pull cable). Crew was rusty, possible distracted by something else, and failed to notice the throttle split. Aircraft rolled due to the thrust asymmetry, crew caught off-guard by sudden AP disconnect, lost SA, and did all the wrong things. Specifics of why the crew failed to react appropriately to a relatively benign failure will remain a mystery unless the CVR memory module is located.
Critics and lawyers will try to blame Boeing (deep pockets - unlike the operator), ignoring that the autothrottle defect had existed and gone uncorrected for some time, and SOP for the pilots is to monitor T/L position and engine parameters.
Critics and lawyers will try to blame Boeing (deep pockets - unlike the operator), ignoring that the autothrottle defect had existed and gone uncorrected for some time, and SOP for the pilots is to monitor T/L position and engine parameters.
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Preliminary KNKT Accident Report is published: http://knkt.dephub.go.id/knkt/ntsc_a...y%20Report.pdf
"The thrust lever position of the left engine continued decreasing while the right engine thrust lever remained."
Aircraft rolled to the left...
"The thrust lever position of the left engine continued decreasing while the right engine thrust lever remained."
Aircraft rolled to the left...
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Left engine thrust lever and corresponding left engine N1 decreasing. Pilots preocupied with ATC communication and bad weather, requesting heading change due to weather and then ATC ordering leveling off at 11.000 feet due to traffic. Further reduction in left engine thrust. AP disconnection followed by rapid left roll past 45 degrees. End of recording only 20 sec later.
No FDR readout provided in the report. Problems with the AT in the days before the accident.
No FDR readout provided in the report. Problems with the AT in the days before the accident.
The virtual absence of FDR data, apart from a handful of snapshots, is unusual compared to recent KNKT preliminary reports.
There is no indication of how, during the last 20 seconds of flight, the aircraft progressed from an "over 45°" left bank (QRH criterion for an upset condition) to a RH spiral descent.
There is no indication of how, during the last 20 seconds of flight, the aircraft progressed from an "over 45°" left bank (QRH criterion for an upset condition) to a RH spiral descent.
Maybe. Maybe not.
It just seems rather strange to describe a 180° roll (if indeed that's what occurred) simply as "over 45°". There are no references to "inverted" anywhere in the preliminary report, which would seem a curious omission if the case.
It just seems rather strange to describe a 180° roll (if indeed that's what occurred) simply as "over 45°". There are no references to "inverted" anywhere in the preliminary report, which would seem a curious omission if the case.
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And the problems were "fixed" by cleaning the contacts. This is reminiscent of the "fixes" done to the Inertial Reference Systems before the AdamAir accident in 2007. From the Final Report (ASN link):
Didn't work then, and probably didn't work now.
The actions to rectify the defects were mainly re-racking, contact cleaning, and relay replacement. See section 1.18.10 for further information.
(When I flew B737, we were told to have hand on thrust levers whenever they were expected to move, e.g. levelling off from a climb.)
The autopilot suddenly dropping out would have been the final straw - the ailerons were being held hard over, but once the autopilot dropped out they would have returned to neutral, and unless correct manual action was taken quickly, the pilots would have been hard pushed to retain control.
Perhaps there should be some sort of alarm that the autopilot is approaching its drop-out point, so crews would know before it actually happens?
(Pax) Sorry to butt in but can someone explain to me what ' off axis entry into a microburst' means pls as I can't follow the discussion. Does it just mean asymmetric wrt the centreline of the aircraft? Thanks.
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And the BITE result - obvious after the first repair attempt - wasn't a good indication if the repair was effective. Nevertheless it was sufficient for sign off after the third try.
How are these situations supposed to be handled by maintenance?
How are these situations supposed to be handled by maintenance?
Uplinker, Different causes, I know, but the result not unlike this one:- https://en.wikipedia.org/wiki/China_Airlines_Flight_006
It sounds like an asymmetric situation was badly mishandled. More thrust on one side than the other, anyone with a multi engine rating knows what happens next. The cause could just as easily have been a real engine failure, the result was the same.
Six years ago TransAsia flight 235, an ATR72 crashed in Taiwan after the crew proved unable to control a twin on one engine. The regulator required all the operators pilots to undertake a test in the simulator in handling an engine failure, not all passed.
Six years ago TransAsia flight 235, an ATR72 crashed in Taiwan after the crew proved unable to control a twin on one engine. The regulator required all the operators pilots to undertake a test in the simulator in handling an engine failure, not all passed.
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Why would the thrust lever of the left engine reduce?
The preliminary report says that the "thrust lever of the left engine started reducing, while the thrust lever position of the right engine remained." Assuming the RH remained at a high power setting, I cannot see whey the LH thrust lever would start coming back.
The A/T drives both levers together, if one jams, the other lever still moves. If the motor fails, the levers will stay in the last position. Both levers run off the same air data source so one would not be commanded to drive back.
I can see no reason why the A/T would drive one lever back, or if the clutch slips the lever would fall back itself.
The A/T drives both levers together, if one jams, the other lever still moves. If the motor fails, the levers will stay in the last position. Both levers run off the same air data source so one would not be commanded to drive back.
I can see no reason why the A/T would drive one lever back, or if the clutch slips the lever would fall back itself.
With nose low:
1. BOTH thrust levers to idle.
2. Unload the wings (ie push to less than 1g).
3. Roll wings level (nearest horizon).
4. Pull nose up towards horizon.
5. Set an appropriate attitude and smoothly increase thrust (5 degrees & climb thrust are good ballpark settings).
6. Take a few slow deep breathes.
Note: If at recovery step 5 and you still have asymmetric thrust, increasing thrust will need to be combined with coordinated rudder to prevent yaw.
1. BOTH thrust levers to idle.
2. Unload the wings (ie push to less than 1g).
3. Roll wings level (nearest horizon).
4. Pull nose up towards horizon.
5. Set an appropriate attitude and smoothly increase thrust (5 degrees & climb thrust are good ballpark settings).
6. Take a few slow deep breathes.
Note: If at recovery step 5 and you still have asymmetric thrust, increasing thrust will need to be combined with coordinated rudder to prevent yaw.
Last edited by Bleve; 10th Feb 2021 at 11:10.
@FiveGirlKit:
The auto-thrust computer will change from commanding climb thrust to looking at IAS when levelling off from a climb. The IAS will increase, so auto-thrust starts pulling the levers back. It does this via motors* which engage to the levers via clutches which are designed to slip above a certain torque.
One thrust lever jams with its engine at climb thrust but the auto-thrust does not know this, it only knows the IAS is still increasing, so it keeps driving the motors to pull both levers back. One lever is still stuck on climb thrust, so the auto-thrust keeps driving the motors to pull both levers back - but only one lever moves; the other lever is jammed and its clutch slips.
In this way you could end up with one engine at, say, 87% N1 and the other at say 35% N1 - a big split.
*Edit: Sorry, I originally claimed one motor for both levers, which is not the case. My bad.
.
The auto-thrust computer will change from commanding climb thrust to looking at IAS when levelling off from a climb. The IAS will increase, so auto-thrust starts pulling the levers back. It does this via motors* which engage to the levers via clutches which are designed to slip above a certain torque.
One thrust lever jams with its engine at climb thrust but the auto-thrust does not know this, it only knows the IAS is still increasing, so it keeps driving the motors to pull both levers back. One lever is still stuck on climb thrust, so the auto-thrust keeps driving the motors to pull both levers back - but only one lever moves; the other lever is jammed and its clutch slips.
In this way you could end up with one engine at, say, 87% N1 and the other at say 35% N1 - a big split.
*Edit: Sorry, I originally claimed one motor for both levers, which is not the case. My bad.
.
Last edited by Uplinker; 10th Feb 2021 at 14:30.
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knkt.go.id/public/files/uploads/posts/posts/postbody/ip.201-1-13-knkt-2021.pdf
Preliminary report of Sriwijaya Air crash.. (sorry in Indonesian languange. Use google translate copy paste to translate).
From Report..
1. Auto Throttle broken. Repaired twice.
2. During take off AT pulls back left engine. AP engaged around 2000 feet.
3. At around 8000 feet, AT again pulls left engine down. Right Engine stays. Continue climb.
4. At 10600 feet, AT again pulls left engine. Right engine stays.
5. Altitude drop. Pitch nose up. Roll started (to left). Then AP disengage. Then nose pitch down.
6. FDR stops recording after 20 seconds. No detail data released.
What can cause AT to pulls 1 engine? Too much engine's vibrations? Faulty sensor data, computer error? Or, (God forbids) thrust reverser deployed during flights?
The preliminary report doesn't explain what pilot do next after 3rd AT pulls down left engine. But i find it hard to believe, even for (i apologize to use the word) un-intelligence pilot NOT to noticed that 1 of the engine start pulling down power, and creates rolls. OR am i wrong? I'm not pilot btw. I just curious (my background is electronics).
That's the latest news from Sriwijaya accident report (preliminary)..
Preliminary report of Sriwijaya Air crash.. (sorry in Indonesian languange. Use google translate copy paste to translate).
From Report..
1. Auto Throttle broken. Repaired twice.
2. During take off AT pulls back left engine. AP engaged around 2000 feet.
3. At around 8000 feet, AT again pulls left engine down. Right Engine stays. Continue climb.
4. At 10600 feet, AT again pulls left engine. Right engine stays.
5. Altitude drop. Pitch nose up. Roll started (to left). Then AP disengage. Then nose pitch down.
6. FDR stops recording after 20 seconds. No detail data released.
What can cause AT to pulls 1 engine? Too much engine's vibrations? Faulty sensor data, computer error? Or, (God forbids) thrust reverser deployed during flights?
The preliminary report doesn't explain what pilot do next after 3rd AT pulls down left engine. But i find it hard to believe, even for (i apologize to use the word) un-intelligence pilot NOT to noticed that 1 of the engine start pulling down power, and creates rolls. OR am i wrong? I'm not pilot btw. I just curious (my background is electronics).
That's the latest news from Sriwijaya accident report (preliminary)..
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Uplinker
That's not true. 737 A/T has two servomechanisms, one per each lever. Have a look at
, particularly around 0:45, where you will see that A/T can move each thrust lever separately.
This functionality is required to synchronize the engine RPM, as the same thrust lever angle might not result in exactly the same N1, depending on many factors, particularly with these hydromechanically-controlled engines.
That's not true. 737 A/T has two servomechanisms, one per each lever. Have a look at
This functionality is required to synchronize the engine RPM, as the same thrust lever angle might not result in exactly the same N1, depending on many factors, particularly with these hydromechanically-controlled engines.
FiveGirlKit
The left thrust lever has operated correctly; the problem is that in response to a thrust reduction command, when the climb mode of FLCH/VNAV - THR; changing to ALT CAP -SPD, that gives a thrust reduction. In the first instance, the left thrust lever comes back slightly, as the AT tries to maintain the commanded speed, which will probably be 250KCAS. As the RT TL is not being picked up by the clutch, the AT will increase the thrust reduction command, and effectively close the LH TL to idle or near that.
At 35 bank the GPWS Mode 6 "BANK ANGLE " sounds continuously. If the bank angle of 45 is correct, then sometime thereafter the APLT has disconnected, which can be determined how, and the aileron that has been applied has to be taken over by the pilot, which is probably not the case. Disconnect with a large aileron deflection often ends up with inadequate force to maintain the existing displacement and a return to a near-neutral aileron is highly likely. At that point, the roll rate is going to accelerate away from desired bank due to the yaw that still remains. The roll rate from the yaw is around 25/s so the aircraft is at 90 bank in a couple of seconds, and what the crew then do is going to be a major factor. the roll to the right is compromised by the more than 90-degree deflection needed on the yoke, but of all of the potential upsets, a captain in the left seat is going to get more right aileron on than the FO, If they are using their outboard hand only. If they grab the controls by both hands, then they have a reduced likelihood of getting full aileron on. With a bank of 90, more RH aileron is required as the natural tendency is then for the nose to fall and that increases the yaw and the subsequent roll rate, so it is not surprising that the crew get confused. (1994 Buff bingle Fairchild, "Budd" Holland and his unfortunate crew.... 2010 Elmendorf C-17 is slightly different, but kind of close) Approaching this point, the nose is going to start slicing down, and speed is going to start to increase, but so will the g loading, so initially the speed will not build rapidly. if the aircraft stalls (not necessary to have this event) the aircraft will rapidly roll inverted, and the nose will drop towards vertical promptly. Speed will increase rapidly but the plane steeply noses down, possibly still with the asymmetry complicating the recovery. Without a stall, speed/aoa stability will assure that the aircraft at the 90 bank or steeper will start loading up, and as soon as the vector is below horizontal, the g will build up rapidly, and the aircraft is going to have a steep spiral, It is possible the crew follow through with the roll at that point, it wouldn't be the first occasion of a crew doing that (B717 stall wild ride) It is conceivable that the aircraft recorder ends with the TLs still split, LH at idle, RH at climb thrust. There are surprisingly few ways to get from A to B in the time available; from the first report, a roll excursion was likely. reminiscent of Sharm Al Sheik.
The left thrust lever has operated correctly; the problem is that in response to a thrust reduction command, when the climb mode of FLCH/VNAV - THR; changing to ALT CAP -SPD, that gives a thrust reduction. In the first instance, the left thrust lever comes back slightly, as the AT tries to maintain the commanded speed, which will probably be 250KCAS. As the RT TL is not being picked up by the clutch, the AT will increase the thrust reduction command, and effectively close the LH TL to idle or near that.
At 35 bank the GPWS Mode 6 "BANK ANGLE " sounds continuously. If the bank angle of 45 is correct, then sometime thereafter the APLT has disconnected, which can be determined how, and the aileron that has been applied has to be taken over by the pilot, which is probably not the case. Disconnect with a large aileron deflection often ends up with inadequate force to maintain the existing displacement and a return to a near-neutral aileron is highly likely. At that point, the roll rate is going to accelerate away from desired bank due to the yaw that still remains. The roll rate from the yaw is around 25/s so the aircraft is at 90 bank in a couple of seconds, and what the crew then do is going to be a major factor. the roll to the right is compromised by the more than 90-degree deflection needed on the yoke, but of all of the potential upsets, a captain in the left seat is going to get more right aileron on than the FO, If they are using their outboard hand only. If they grab the controls by both hands, then they have a reduced likelihood of getting full aileron on. With a bank of 90, more RH aileron is required as the natural tendency is then for the nose to fall and that increases the yaw and the subsequent roll rate, so it is not surprising that the crew get confused. (1994 Buff bingle Fairchild, "Budd" Holland and his unfortunate crew.... 2010 Elmendorf C-17 is slightly different, but kind of close) Approaching this point, the nose is going to start slicing down, and speed is going to start to increase, but so will the g loading, so initially the speed will not build rapidly. if the aircraft stalls (not necessary to have this event) the aircraft will rapidly roll inverted, and the nose will drop towards vertical promptly. Speed will increase rapidly but the plane steeply noses down, possibly still with the asymmetry complicating the recovery. Without a stall, speed/aoa stability will assure that the aircraft at the 90 bank or steeper will start loading up, and as soon as the vector is below horizontal, the g will build up rapidly, and the aircraft is going to have a steep spiral, It is possible the crew follow through with the roll at that point, it wouldn't be the first occasion of a crew doing that (B717 stall wild ride) It is conceivable that the aircraft recorder ends with the TLs still split, LH at idle, RH at climb thrust. There are surprisingly few ways to get from A to B in the time available; from the first report, a roll excursion was likely. reminiscent of Sharm Al Sheik.