737-500 missing in Indonesia
ATC Watcher
I'm going to respond to several different posts here - although this one is the most pertinent.
Speaking Boeing specifically here - Airbus is different. The older cable controlled engines did sometimes suffer clutch slippage - usually due to high down stream cable loads (such as a seized pulley or a damaged push/pull cable). This could case one throttle to either not move, or to move at a slower rate than the other(s). It will not cause the throttle to unilaterally advance or retard - simply fail to move or move at a slower rate as the clutch slips, so it's primarily a concern with large throttle movements. The transition to FADEC has nearly eliminated this issue - FADEC thrust levers do not use a clutch, they have relatively simple friction device to prevent the thrust levers from uncommanded movement due to dynamic loads - there is almost zero force required to move the FADEC lever position resolvers (the friction devices are set to about 2 lbs. force at the lever). However, it is still possible for a FADEC thrust lever to slip during A/T movement if there is some obstruction - e.g. someone drops a pen or other debris into the thrust lever quadrant.
A good accident investigator 'never says never' - however the causes of the rudder hardover and the Lauda in-flight T/R deployment were identified, and corrective action taken via AD over 20 years ago. Since this aircraft was originally owned by United, it's rather certain that the fixes were incorporated, so it's highly unlikely that one of those was the cause. Furthermore, both would be quickly obvious during the initial review of the FDR data. Since there are still thousands of 737-3/4/500 aircraft out there, there would be urgency in getting that cause public so that checks could be made of other in-service aircraft.
I'm going to respond to several different posts here - although this one is the most pertinent.
Speaking Boeing specifically here - Airbus is different. The older cable controlled engines did sometimes suffer clutch slippage - usually due to high down stream cable loads (such as a seized pulley or a damaged push/pull cable). This could case one throttle to either not move, or to move at a slower rate than the other(s). It will not cause the throttle to unilaterally advance or retard - simply fail to move or move at a slower rate as the clutch slips, so it's primarily a concern with large throttle movements. The transition to FADEC has nearly eliminated this issue - FADEC thrust levers do not use a clutch, they have relatively simple friction device to prevent the thrust levers from uncommanded movement due to dynamic loads - there is almost zero force required to move the FADEC lever position resolvers (the friction devices are set to about 2 lbs. force at the lever). However, it is still possible for a FADEC thrust lever to slip during A/T movement if there is some obstruction - e.g. someone drops a pen or other debris into the thrust lever quadrant.
A good accident investigator 'never says never' - however the causes of the rudder hardover and the Lauda in-flight T/R deployment were identified, and corrective action taken via AD over 20 years ago. Since this aircraft was originally owned by United, it's rather certain that the fixes were incorporated, so it's highly unlikely that one of those was the cause. Furthermore, both would be quickly obvious during the initial review of the FDR data. Since there are still thousands of 737-3/4/500 aircraft out there, there would be urgency in getting that cause public so that checks could be made of other in-service aircraft.
Last edited by tdracer; 23rd Jan 2021 at 07:59. Reason: typo
Thrust disparity between engines seems to be what investigators are looking at. I wonder if China Airlines 006 may offer a scenario. From Wiki.
Following failure of engine #4 airspeed continued to decrease, and the autopilot rolled the control wheel to the maximum left limit of 23 degrees. As the speed decreased even further, the plane began to roll to the right, even though the autopilot was maintaining the maximum left roll limit. By the time the captain disconnected the autopilot, the plane had rolled over 60 degrees to the right and the nose had begun to drop. Ailerons and flight spoilers were the only means available to the autopilot to keep the wings level as the autopilot does not connect to the rudder during normal flight. To counteract the asymmetrical forces created by the loss of thrust from the No. 4 engine, it was essential for the pilot to manually push on the left rudder. However, the captain failed to use any rudder inputs at all, before or after disconnecting the autopilot.As the plane descended through clouds, the captain's attention was drawn to the attitude indicator which displayed excessive bank and pitch. Because such an attitude is highly irregular, the captain incorrectly assumed the indicators to be faulty. Without any visual references (due to the clouds) and having rejected the information from the attitude indicators, the captain and first officer became spatially disoriented.
I hate to sound a clever dick, but until the FDR is read and there is evidence of an asymmetric condition, then we are all guessing what would have caused the final dive.
That said, on numerous occasions as an instructor during simulator training I have "arranged" a clutch failure in the 737 Classic simulator at certain phases of flight. Sometimes this would occur as TOGA was selected at the start of the run, and other times while the throttles were idle during a clean descent. Then when power was needed, only one throttle would move. Where the students have been briefed beforehand of the symptoms of clutch failure on one throttle and the recovery actions (simply use the throttle manually) we found some students would quickly take corrective action before the flight path got out of hand.
On the occasions where students had not been alerted to an impending clutch failure during the preflight briefing, there were some who recognised there was a throttle problem and used normal airmanship to rectify any roll or yaw. There were others who seemed to have been so bemused that they failed to apply immediate corrective action until it was too late to recover. Read Post 310 as an example. So much depended on the flying ability of the pilot. It was those pilots who were automation dependant who were the bemused.
That said, on numerous occasions as an instructor during simulator training I have "arranged" a clutch failure in the 737 Classic simulator at certain phases of flight. Sometimes this would occur as TOGA was selected at the start of the run, and other times while the throttles were idle during a clean descent. Then when power was needed, only one throttle would move. Where the students have been briefed beforehand of the symptoms of clutch failure on one throttle and the recovery actions (simply use the throttle manually) we found some students would quickly take corrective action before the flight path got out of hand.
On the occasions where students had not been alerted to an impending clutch failure during the preflight briefing, there were some who recognised there was a throttle problem and used normal airmanship to rectify any roll or yaw. There were others who seemed to have been so bemused that they failed to apply immediate corrective action until it was too late to recover. Read Post 310 as an example. So much depended on the flying ability of the pilot. It was those pilots who were automation dependant who were the bemused.
The later pitch (not AVIAT.) in this thread seems familiar to me ... and I don't like it.
Having said that and not flying heavy iron:
I can understand not noticing split throttles timely.
I can understand not noticing a rudder input by AP (which can be ruled out due to 2 channels only?)
I cannot understand not noticing a significant aileron input by AP during wings level climb.
Maybe some 737 classic driver can elaborate on that?
Having said that and not flying heavy iron:
I can understand not noticing split throttles timely.
I can understand not noticing a rudder input by AP (which can be ruled out due to 2 channels only?)
I cannot understand not noticing a significant aileron input by AP during wings level climb.
Maybe some 737 classic driver can elaborate on that?
Why? NGs do not have an a/p yaw channel...the resulting slip should be absolutely unmissable to all but someone asleep. It would feel horrible!
Agree, what does the DFDR latch on these machines relative to on or off warnings. It would seem that even if the DFDR is still under review that certain warnings of such magnitude would already have leaked out. I've done some stuff where even before I could make it to the end of the day critical dfdr warnings had already leaked out.
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Re A/T in the news,
My biggest gripe with the 737-5 was the very insiduous disconnect of the A/T - no master warning or caution, unlike the A/P disconnect siren. Only a “click” of the switch flicking off. Very easy to not notice that you’d lost your A/T if you weren’t vigorous with your FMA’s AND by keeping your hands on your thrust levers.
at first mention of an A/T issue, my initial thoughts would be a chain of events such as - automatics disconnect, loss of speed, leading to a stall, leading to a loss of control by improper yoke input eg colgan, AF447 etc.
My biggest gripe with the 737-5 was the very insiduous disconnect of the A/T - no master warning or caution, unlike the A/P disconnect siren. Only a “click” of the switch flicking off. Very easy to not notice that you’d lost your A/T if you weren’t vigorous with your FMA’s AND by keeping your hands on your thrust levers.
at first mention of an A/T issue, my initial thoughts would be a chain of events such as - automatics disconnect, loss of speed, leading to a stall, leading to a loss of control by improper yoke input eg colgan, AF447 etc.
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I used to fly the classic and one thing I found was that it was hard to work out if you had the right amount of rudder with an engine failed / idle if the autopilot was making a turn. You use the control column being centralised to know if you have the correct amount of rudder. That’s not possible if the autopilot is rolling into or out of a turn.
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Propellerhead you are correct it’s harder in a turn but the slip indicator will tell what you need to know under these circumstances.
Watched an inexperienced first office in the sim recently trying to get the aircraft in trim during a turn. Struggled slightly but the slip indicator was way off centre and that was the big clue as to wether he had applied too much or not enough rudder.
Back to basics which unfortunately don’t get taught these days.
Watched an inexperienced first office in the sim recently trying to get the aircraft in trim during a turn. Struggled slightly but the slip indicator was way off centre and that was the big clue as to wether he had applied too much or not enough rudder.
Back to basics which unfortunately don’t get taught these days.
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Was this on a NG? On the CL the slip indicator is hard to look at especially in the sim. It's under the EADI but the only reference is the control wheel, which should be kept level.
I don't even know if the slip indicator on the CL simulator is there just as a fitting or if it could be referenced reliably.
I don't even know if the slip indicator on the CL simulator is there just as a fitting or if it could be referenced reliably.
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Yes it was an NG sim. The slip indicator is a bar under the pointer on the pfd.
Very clear and obvious assuming of course you know to look at it.
This combined with control wheel as you suggest reinforces in trim condition.
Very clear and obvious assuming of course you know to look at it.
This combined with control wheel as you suggest reinforces in trim condition.
SLF here. I'm trying to wrap my head around discussions here; are posters suggesting this accident might be similar to a single engine loss of power in a light twin, with speed below Vmc and a consequent roll and ....
oblivia
They may care, but only as they see it affecting their bottom line and their judgment about the cost of safety vs the probability and cost of accident is flawed.
it happened over time, the accumulation of bad management decisions with less than obvious consequences compared to the immediate and obvious costs.
They may care, but only as they see it affecting their bottom line and their judgment about the cost of safety vs the probability and cost of accident is flawed.
it happened over time, the accumulation of bad management decisions with less than obvious consequences compared to the immediate and obvious costs.