737-500 missing in Indonesia
Winemaker
The suggestion was made that it’s possible for the auto thrust clutch to fail, and that could lead to the power of one engine to reduce, possibly all the way back to idle. I’m not on plan B, so not sure if they are suggesting the throttle itself would move too, but I would guess it would. Having one engine at idle, and the other at climb thrust would obviously induce a yaw. If this would happen with the autopilot on, the autopilot would try to maintain the path with ailerons deflection, but it has no automatic rudder trim, so the aircraft would have a sideslip. I would think that as long as they were climbing in an airspeed mode the speed would not have gotten low enough to get near to any Vmc condition. It is possible that, perhaps because of the loss of performance the pilots selected a higher climb rate using vertical speed, and the speed loss that followed lead to an autopilot disconnect and loss of control because of the out of trim situation, but that is pure speculation.
The suggestion was made that it’s possible for the auto thrust clutch to fail, and that could lead to the power of one engine to reduce, possibly all the way back to idle. I’m not on plan B, so not sure if they are suggesting the throttle itself would move too, but I would guess it would. Having one engine at idle, and the other at climb thrust would obviously induce a yaw. If this would happen with the autopilot on, the autopilot would try to maintain the path with ailerons deflection, but it has no automatic rudder trim, so the aircraft would have a sideslip. I would think that as long as they were climbing in an airspeed mode the speed would not have gotten low enough to get near to any Vmc condition. It is possible that, perhaps because of the loss of performance the pilots selected a higher climb rate using vertical speed, and the speed loss that followed lead to an autopilot disconnect and loss of control because of the out of trim situation, but that is pure speculation.
hans brinker
The thrust lever won't close by itself ordinarily, although there is one particular case where that certainly will occur. A clutch problem will leave the thrust lever at a position, anywhere along the available TLA's.
The problem with an asymmetry while on APLT and without rudder input is not a VMCA issue, it is simply that there is an APLT roll input to maintain attitude due to uncorrected yaw, and the APLT will happily apply the roll input until it doesn't. If the APLT roll authority is limited, then eventually a roll-off that exceeds the APLT limits can occur and the APLT disconnects. at that time, the Roll input is removed, the yaw remains and a rapid roll occurs. The authority to stop the roll is lower than normal due to the roll induced by the yaw, so recovery is less than expected in normal handling, and on occasions that has resulted in confusion in the cockpit. (I observed that in a B744 on one occasion, and the roll in the screw up was sufficient o leave a well-deserved scar on the loopy captain's RH forehead from the storm light switch poetically shaped as a blade).
Within the normal envelope of the APLT, if the APLT is disconnected the crew may not be ready for the removal of the force of the APLT on the ailerons, which will rapidly return to neutral unless counted by the driver. That may seem obvious, especially when the driver is going to be trying to pickle off the APLT from a control position that is decidedly not neutral, but often crew will not be ready for the loads that are being assumed by them to maintain the current control position. An insidious problem can be encountered as well if the driver happens to mistakenly use aileron trim instead of rudder trim while the APLT is engaged. On too many aircraft, doing that will not disconnect the APLT immediately where using the stab trim will, but the extent of trim input is not observable on say, Boeings... and so a wild ride can occur at disconnect if it is not recognized.
All of these issues should be nonissues, but then that is the case with most accidents and most human endeavours; when the humans understanding of their state differs from actual, wild rides happen. If you are not used to wild rides (and even when you are) they can escalate rapidly as the human scurries to get back into the loop, which means doing all of the OODA stuff in quick time. The normal envelope of +/- 35, +25/-10 (or whatever the limits of your ride are set at) leaves a lot of attitudes and accelerations that the driver doesn't get to spend time experiencing.
The thrust lever won't close by itself ordinarily, although there is one particular case where that certainly will occur. A clutch problem will leave the thrust lever at a position, anywhere along the available TLA's.
The problem with an asymmetry while on APLT and without rudder input is not a VMCA issue, it is simply that there is an APLT roll input to maintain attitude due to uncorrected yaw, and the APLT will happily apply the roll input until it doesn't. If the APLT roll authority is limited, then eventually a roll-off that exceeds the APLT limits can occur and the APLT disconnects. at that time, the Roll input is removed, the yaw remains and a rapid roll occurs. The authority to stop the roll is lower than normal due to the roll induced by the yaw, so recovery is less than expected in normal handling, and on occasions that has resulted in confusion in the cockpit. (I observed that in a B744 on one occasion, and the roll in the screw up was sufficient o leave a well-deserved scar on the loopy captain's RH forehead from the storm light switch poetically shaped as a blade).
Within the normal envelope of the APLT, if the APLT is disconnected the crew may not be ready for the removal of the force of the APLT on the ailerons, which will rapidly return to neutral unless counted by the driver. That may seem obvious, especially when the driver is going to be trying to pickle off the APLT from a control position that is decidedly not neutral, but often crew will not be ready for the loads that are being assumed by them to maintain the current control position. An insidious problem can be encountered as well if the driver happens to mistakenly use aileron trim instead of rudder trim while the APLT is engaged. On too many aircraft, doing that will not disconnect the APLT immediately where using the stab trim will, but the extent of trim input is not observable on say, Boeings... and so a wild ride can occur at disconnect if it is not recognized.
All of these issues should be nonissues, but then that is the case with most accidents and most human endeavours; when the humans understanding of their state differs from actual, wild rides happen. If you are not used to wild rides (and even when you are) they can escalate rapidly as the human scurries to get back into the loop, which means doing all of the OODA stuff in quick time. The normal envelope of +/- 35, +25/-10 (or whatever the limits of your ride are set at) leaves a lot of attitudes and accelerations that the driver doesn't get to spend time experiencing.
Tim27
Not only that a hand should be on thrust levers at ALL times when the AT is active. Ie when making significant movements. Caught out the guys in Emirates, big time, crashing a perfectly serviceable jet.
....and during a coupled approach hard to believe that guys are not following through on both yoke and thrust levers.
Not only that a hand should be on thrust levers at ALL times when the AT is active. Ie when making significant movements. Caught out the guys in Emirates, big time, crashing a perfectly serviceable jet.
....and during a coupled approach hard to believe that guys are not following through on both yoke and thrust levers.
All of these issues should be nonissues, but then that is the case with most accidents and most human endeavours; when the humans understanding of their state differs from actual, wild rides happen. If you are not used to wild rides (and even when you are) they can escalate rapidly as the human scurries to get back into the loop, which means doing all of the OODA stuff in quick time. The normal envelope of +/- 35, +25/-10 (or whatever the limits of your ride are set at) leaves a lot of attitudes and accelerations that the driver doesn't get to spend time experiencing.
Surely every airline SOP mandates on a coupled approach, following through, hands on controls and thrust levers during final approaches. (My Company B 747,below 1000ft.) And most importantly on a Go Around. EK would not have lost the 777 at DXB, due this omission.
Basic Airmanship?
Basic Airmanship?
Last edited by cessnapete; 29th Jan 2021 at 08:33.
Some aircraft may require 'follow through' from certification.
e.g. autopilot runaway above 1000 ft may use a 4 sec reaction time. Below 1000 ft, 2 sec could apply providing the pilots is 'hands on' to reduce height loss, quicker reaction.
jimtx, if you imply that you are over-riding the autopilot - applying force other than that from the AP, then be prepared for a surprise: - back driven trim, sudden force disconnect.
e.g. autopilot runaway above 1000 ft may use a 4 sec reaction time. Below 1000 ft, 2 sec could apply providing the pilots is 'hands on' to reduce height loss, quicker reaction.
jimtx, if you imply that you are over-riding the autopilot - applying force other than that from the AP, then be prepared for a surprise: - back driven trim, sudden force disconnect.
Icarus2001
As do the crews that end up out of sorts. UAL, USAir, etc had upset training before 587, 585, 427... and had bad days. So did a bunch of 604 drivers, AF447 etc. Now, before the cries of but the b737 rudder PCU....!, note that the roll rates were well above flight control available rates, so autorotative effects were in pkay on 427 and 585, and lo, 427 elevators are NU throughout the sad event. 585 rates... Etc.. NTSB was silent on rates achieved.
Anyway, if you aren't in the head, have conpetency and are aware of what and preferably why, and are not inconvenienced by the accelerations and vibrations at your seat, then it is all good. For the rest, the training hopefully gives a capability to sort out what they got and undo it.
The B717 stall video shows a competent crew having a wild old ride.. As did perpignan. A while back i did a BFR in a SE jet with a sharp examiner. While he was doing a barrel roll it turned into a half cuban, but with an entry of around 350kts... And not so much height for what then occurred, an indecision on which way to roll, he had to look behind the wing or in the mirror for the horizon, and then he went for a pull through rather than a roll out to a recovery, which was at about 450kts indicated and 7g. We were well clear of the ground, but not by design. It had enough margin for the recovery to be talked through, but the split S was not a manoeuver i was expecting to see a good driver get into outbof a barrel roll. Post flight, the examiner noted he was disoriented with trying to acquire the horizon and needed to follow the recovery that was being called. It was a non event, but was still curious in the recovery attempted and the reason why. There but for Grace etc...
As do the crews that end up out of sorts. UAL, USAir, etc had upset training before 587, 585, 427... and had bad days. So did a bunch of 604 drivers, AF447 etc. Now, before the cries of but the b737 rudder PCU....!, note that the roll rates were well above flight control available rates, so autorotative effects were in pkay on 427 and 585, and lo, 427 elevators are NU throughout the sad event. 585 rates... Etc.. NTSB was silent on rates achieved.
Anyway, if you aren't in the head, have conpetency and are aware of what and preferably why, and are not inconvenienced by the accelerations and vibrations at your seat, then it is all good. For the rest, the training hopefully gives a capability to sort out what they got and undo it.
The B717 stall video shows a competent crew having a wild old ride.. As did perpignan. A while back i did a BFR in a SE jet with a sharp examiner. While he was doing a barrel roll it turned into a half cuban, but with an entry of around 350kts... And not so much height for what then occurred, an indecision on which way to roll, he had to look behind the wing or in the mirror for the horizon, and then he went for a pull through rather than a roll out to a recovery, which was at about 450kts indicated and 7g. We were well clear of the ground, but not by design. It had enough margin for the recovery to be talked through, but the split S was not a manoeuver i was expecting to see a good driver get into outbof a barrel roll. Post flight, the examiner noted he was disoriented with trying to acquire the horizon and needed to follow the recovery that was being called. It was a non event, but was still curious in the recovery attempted and the reason why. There but for Grace etc...
Last edited by fdr; 31st Jan 2021 at 03:29.
Join Date: Jan 2015
Location: Banksville
Posts: 70
Likes: 0
Received 0 Likes
on
0 Posts
I’d be interested to know from any 737 drivers here, how obvious a sideslip is when engine thrust is asymmetrical. I assume it much depends on how out of balance the thrust is, but....something you can feel easily in seat of pants?....
When you are disorientated, seat of the pants does not help. AF 447 descended at 10000ft/min yet the crew held the stick full back. Although I did 'upset training' in the commercial world it was of little use and I relied upon training received in the military.
Join Date: Aug 2002
Location: Castletown
Posts: 241
Likes: 0
Received 0 Likes
on
0 Posts
Joejosh999
Depends on the situation at the time of engine failure.
If the autopilot is engaged in level flight for example, then the control wheel will be displaced (turn) towards the "live" engine. If there is no rudder input to counteract yaw, then the autopilot will disconnect when the AFDS cannot cope.
Without an autopilot engaged, then the turn and slip indicator will show the pilot the sideslip. Boeing do not recommend trimming the rudder to completely get rid of the sideslip, as a "neutral" control column is desired which avoids inadvertent spoiler extension which causes increased drag and a reduction in lift.
Depends on the situation at the time of engine failure.
If the autopilot is engaged in level flight for example, then the control wheel will be displaced (turn) towards the "live" engine. If there is no rudder input to counteract yaw, then the autopilot will disconnect when the AFDS cannot cope.
Without an autopilot engaged, then the turn and slip indicator will show the pilot the sideslip. Boeing do not recommend trimming the rudder to completely get rid of the sideslip, as a "neutral" control column is desired which avoids inadvertent spoiler extension which causes increased drag and a reduction in lift.
Join Date: Nov 2002
Location: Dublin
Posts: 652
Likes: 0
Received 0 Likes
on
0 Posts
"Depends on the situation at the time of engine failure"..correct,
During every return to lease flight we do this
CRUISE AT OR ABOVE 37,000 FEETA. DUCT PRESSURE
(1) Check that duct pressure regulates between 34 to 50 psig _____
B. ENGINE ACCELERATION & HIGH STAGE BLEED CROSSOVER
(1) Engine IgnitionCONT
(2) AutothrottleOFF
(3) Maintain stable flight at cruise altitude.
a) FMC N1 page select CON ____
(4) Engine #1
a) Set No. 2 thrust lever to MCT.
b) Rapidly retard No. 1 thrust lever to idle.
c) Check for crossover indicated by sudden duct pressure increase _____
d) Allow RPM and EGT to stabilize.
e) (Timed event) In approx one second advance the No. 1 thrust lever toward MCT. Set thrust lever approx 1 knob width below engine No. 2 to avoid overboost.
Start timing when thrust lever is advanced and stop timing at 90% N1.
f) Record acceleration timesec.
g) Engine should accelerate smoothly and without compressor stalls ____
The reason I post this is to simply emphasise that the aircraft does not fall from the sky or lurch hopelessly one way or the other and a small control column deflection and rudder input is sufficient, the big difference being we are mentally prepared for the event.
If you loose an engine in the climb or turn and do not revert to basic airmanship and problem diagnosis there is a likelihood of the incorrect actions being taken. The A/T should not retard the TL in the climb unless the target altitude had been captured in the MCP +/_ the limits of VNAV or LVL Change, VS does not count here as climb in VS the AT is controlled by the MCP speed. During an engine failure in the climb yaw would be fairly significant, but again, there would be no commands to the AT servos unless some signals had been given to the system either in terms of MCP speed reduction in VS or "Capture" in another mode.
An A/T servo failure during TL retard should be spotted by the crew but is not a reason to have a jet upset and certainly not regarded as so "time critical" that diagnosis cannot be performed. To be honest, the turn and slip is more of a comfort thing, the yoke displacement is a more natural indication and does not lag as much as the ball.
Apart from EFATO, at a safe height, the excessive use of rudder trim is not recommended as unless you are terrain critical and need to continue the climb, as normally you would simply stop the climb and after the diagnosis trim of the QRH recommends it.
The reasons for this accident are yet to be established and the whole engine, TL, AT debate is speculation, it could just as easily be a jammed or broken flight control.
During every return to lease flight we do this
CRUISE AT OR ABOVE 37,000 FEETA. DUCT PRESSURE
(1) Check that duct pressure regulates between 34 to 50 psig _____
B. ENGINE ACCELERATION & HIGH STAGE BLEED CROSSOVER
(1) Engine IgnitionCONT
(2) AutothrottleOFF
(3) Maintain stable flight at cruise altitude.
a) FMC N1 page select CON ____
(4) Engine #1
a) Set No. 2 thrust lever to MCT.
b) Rapidly retard No. 1 thrust lever to idle.
c) Check for crossover indicated by sudden duct pressure increase _____
d) Allow RPM and EGT to stabilize.
e) (Timed event) In approx one second advance the No. 1 thrust lever toward MCT. Set thrust lever approx 1 knob width below engine No. 2 to avoid overboost.
Start timing when thrust lever is advanced and stop timing at 90% N1.
f) Record acceleration timesec.
g) Engine should accelerate smoothly and without compressor stalls ____
The reason I post this is to simply emphasise that the aircraft does not fall from the sky or lurch hopelessly one way or the other and a small control column deflection and rudder input is sufficient, the big difference being we are mentally prepared for the event.
If you loose an engine in the climb or turn and do not revert to basic airmanship and problem diagnosis there is a likelihood of the incorrect actions being taken. The A/T should not retard the TL in the climb unless the target altitude had been captured in the MCP +/_ the limits of VNAV or LVL Change, VS does not count here as climb in VS the AT is controlled by the MCP speed. During an engine failure in the climb yaw would be fairly significant, but again, there would be no commands to the AT servos unless some signals had been given to the system either in terms of MCP speed reduction in VS or "Capture" in another mode.
An A/T servo failure during TL retard should be spotted by the crew but is not a reason to have a jet upset and certainly not regarded as so "time critical" that diagnosis cannot be performed. To be honest, the turn and slip is more of a comfort thing, the yoke displacement is a more natural indication and does not lag as much as the ball.
Apart from EFATO, at a safe height, the excessive use of rudder trim is not recommended as unless you are terrain critical and need to continue the climb, as normally you would simply stop the climb and after the diagnosis trim of the QRH recommends it.
The reasons for this accident are yet to be established and the whole engine, TL, AT debate is speculation, it could just as easily be a jammed or broken flight control.
