Jet 737 aborts takeoff, leaves runway - Goa
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There has been a lot of chat about how this could have happened, both an unlocked reverser or asymmetric thrust could do it ( although fadec would probably limit thrust with a deployed reverser , been a while so not sure on that one ).
Most accurate posts have suggested VMCG and governor failure. A combination of these is almost impossible to control. Usually a governor failure involves an increase in thrust as the engine "runs away" before the fadec shuts it down. As the thrust runs away the pilot instinctively corrects the yaw with rudder. So now we have, let's say right right rudder in, as the right engine runs away. Then fadec shuts it down. Now you have right rudder in with a right engine failure, end result below VMCG is exit stage right.
Not saying this happened here, but any asymmetry below VMCG would be similar.
Most accurate posts have suggested VMCG and governor failure. A combination of these is almost impossible to control. Usually a governor failure involves an increase in thrust as the engine "runs away" before the fadec shuts it down. As the thrust runs away the pilot instinctively corrects the yaw with rudder. So now we have, let's say right right rudder in, as the right engine runs away. Then fadec shuts it down. Now you have right rudder in with a right engine failure, end result below VMCG is exit stage right.
Not saying this happened here, but any asymmetry below VMCG would be similar.
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Quite flummoxed by the runway excursion of #JetAirways Boeing 737-800, VT-JBG at GOI.
A few points:
1. Post accident pictures show the starboard thrust reverser deployed and the port reverser stowed. Is this due to the engine cowlings scraping on the ground or did actual deployment take place? Wonder what the actual position of the TR lever was?
2. Was there an uncommanded deployment of starboard reverser just as take-off power was set? Unlikely in a modern aircraft, but chances are there since aircraft was on ground with weight on wheels. But to my mind, in such a failure case the FADEC should have commanded idle power with a lot of warning bells and whistles going off...
3. Did the pilots spool up the outboard engine to assist the turn, close the levers as they line up and then stand them up to 45-50% when cleared for T/O, however the spooling down engine hasn't fully idled and so it spooled up faster than the other, resulting in a big yaw? Or did they use the TOGA button too early before lining up fully? Or was there an overspeed governor failure where the engine runs away before FADEC shuts it down?
4. Did they use reverse on the inboard engine (in this case – starboard) to assist the turn after a rather fast taxi? For this both power levers would have to be first brought to idle to escape the interlocks. But the aircraft did move forward, therefore forward thrust was available - so this scenario too is unlikely..
5. A low speed asymmetric power event is a difficult thing to handle in the night, without many visual references and no rudder control (below VMCG) being at too low a speed for rudder authority.
Waiting eagerly for proper findings on the DGCA enquiry..
A few points:
1. Post accident pictures show the starboard thrust reverser deployed and the port reverser stowed. Is this due to the engine cowlings scraping on the ground or did actual deployment take place? Wonder what the actual position of the TR lever was?
2. Was there an uncommanded deployment of starboard reverser just as take-off power was set? Unlikely in a modern aircraft, but chances are there since aircraft was on ground with weight on wheels. But to my mind, in such a failure case the FADEC should have commanded idle power with a lot of warning bells and whistles going off...
3. Did the pilots spool up the outboard engine to assist the turn, close the levers as they line up and then stand them up to 45-50% when cleared for T/O, however the spooling down engine hasn't fully idled and so it spooled up faster than the other, resulting in a big yaw? Or did they use the TOGA button too early before lining up fully? Or was there an overspeed governor failure where the engine runs away before FADEC shuts it down?
4. Did they use reverse on the inboard engine (in this case – starboard) to assist the turn after a rather fast taxi? For this both power levers would have to be first brought to idle to escape the interlocks. But the aircraft did move forward, therefore forward thrust was available - so this scenario too is unlikely..
5. A low speed asymmetric power event is a difficult thing to handle in the night, without many visual references and no rudder control (below VMCG) being at too low a speed for rudder authority.
Waiting eagerly for proper findings on the DGCA enquiry..
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seems to have got it spot on here..
Jet Airways' pilot's act was as miraculous as landing aircraft on water
Jet Airways' pilot's act was as miraculous as landing aircraft on water
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Based on information in public domain (read hear say) dishing out accolades is just as bad as sensure of the crew. How will it look if in the inquiry some deficiency is found? No media channels said anything about the crews actions. The evacuation was pathetically handled so some pissed of passangers scared out of their wits said something there is no need for persecution mania. Ultimately accolades by brother in arms or criticism by the ignorant is not going to matter but only the conclusion of the DGCA will prevail.
Last edited by vilas; 31st Dec 2016 at 06:02.
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The article mentions mandatory actions to prevent excursion as three options. All of them are simultaneous actions none of them is an option.If at all thrust reduction including reverse application on the good engine should be the first. That straightens the aircraft and obviates any need to shut down the faulty engine. This is the correct procedure and not arm chair exercise.
Last edited by vilas; 31st Dec 2016 at 11:53.
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I have read elsewhere on an aviation page on a popular social media site that the crew "may" have used reverse on the no2 to assist with the 180 turn, then hit toga once lined up, but before the reverser sleeves/interlocks were fully back in place, so the increasing thrust blew the reverser back open again with said result. That was the only comment of that scenario being speculated that I've seen though.
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Is there anything to confirm uncommanded reverser deployment other than the pictures showing the #2 sleeves deployed (only have observed outer sleeve in pictures) and some unconfirmed accounts?
I have been studying the CFM56-7b thrust reverser (78-34-00) design to understand the barriers for uncommanded reverser deployment. it is designed to prevent this failure from occurring that which has no single pathway (assuming the throttle levers were not physically commanded to reverse thrust). A cascade of failures including multiple independent switch-controlled relays would be necessary for both sync-locks to activate, for both locking actuators to release, and to apply hydraulic power to deploy. No single hardware failure would lead to deployment (the lever/linkage itself is the only common element). There are maintenance procedures to manually deploy and override locks. The logic for on-ground or 10 feet AGL is applied as an additional interlock to the hydraulic commands.
The thrust reverser is not efficient in comparison to forward thrust, especially at low speeds (e.g. effective reverse thrust would be reduced from comparable forward thrust). For sure, there would be no forward thrust when the sleeves deploy the blocking doors (when considering yawing moment).
Until 60 knots, there should be considerable scrutiny on setting takeoff power. With the data suggesting this speed was never achieved, then the pilot monitoring should have had full attention on the engine instruments, and should have noted reverser deployment without any delay. I would have expected both throttles to be slammed to idle in this occurrence, in less than three seconds to allow for reaction, and engines spooled down about three seconds later. That would suggest that the airplane should stop accelerating within about 6 seconds from the failure occurrence. In this case, the considerable loss of directional control left the airplane still accelerating while plowing away.
Two points from the ADS-B reporting:
1) there was at least a minute from when the airplane reversed course in taxi and lined up to the when the airplane began its takeoff roll.
2) the airplane continued to accelerate after departing the runway. Three specific reports were six seconds apart, the first at runway departure (and it about six seconds from initiating the takeoff roll). From departing the runway, peak speed was reported six seconds later and speed was subsiding 12 seconds later.
I have been studying the CFM56-7b thrust reverser (78-34-00) design to understand the barriers for uncommanded reverser deployment. it is designed to prevent this failure from occurring that which has no single pathway (assuming the throttle levers were not physically commanded to reverse thrust). A cascade of failures including multiple independent switch-controlled relays would be necessary for both sync-locks to activate, for both locking actuators to release, and to apply hydraulic power to deploy. No single hardware failure would lead to deployment (the lever/linkage itself is the only common element). There are maintenance procedures to manually deploy and override locks. The logic for on-ground or 10 feet AGL is applied as an additional interlock to the hydraulic commands.
The thrust reverser is not efficient in comparison to forward thrust, especially at low speeds (e.g. effective reverse thrust would be reduced from comparable forward thrust). For sure, there would be no forward thrust when the sleeves deploy the blocking doors (when considering yawing moment).
Until 60 knots, there should be considerable scrutiny on setting takeoff power. With the data suggesting this speed was never achieved, then the pilot monitoring should have had full attention on the engine instruments, and should have noted reverser deployment without any delay. I would have expected both throttles to be slammed to idle in this occurrence, in less than three seconds to allow for reaction, and engines spooled down about three seconds later. That would suggest that the airplane should stop accelerating within about 6 seconds from the failure occurrence. In this case, the considerable loss of directional control left the airplane still accelerating while plowing away.
Two points from the ADS-B reporting:
1) there was at least a minute from when the airplane reversed course in taxi and lined up to the when the airplane began its takeoff roll.
2) the airplane continued to accelerate after departing the runway. Three specific reports were six seconds apart, the first at runway departure (and it about six seconds from initiating the takeoff roll). From departing the runway, peak speed was reported six seconds later and speed was subsiding 12 seconds later.
then the pilot monitoring should have had full attention on the engine instruments
Maybe you meant that the PM should be focussing much of their attention on the engine instruments?
With your rather generous 3 seconds for recognition I think you are departing the runway with full thrust on one and none / reverse on the other if you are below 60kts.
Here is another possible scenario... Ruder pedal jam. Unlikely? maybe not, Boeing know about it.
737NG-FTD-25-15004
Rudder Pedal Motion Restricted
Background
An operator reported that a Rejected Take Off (RTO) was performed at 25 knots after pilot experienced stuck rudder pedals. The airplane returned to the gate safely and the flight crew reported no rudder pedal anomalies prior to takeoff roll. Maintenance found a loose flush-head fastener protruding/interfering with the rudder pedal movement (captains rudder pedal housing, left foot - inboard side). Maintenance subsequently re-torqued the fastener, performed a rudder pedal adjustment and limit test with no findings. A Boeing review of Flight Data Recorder (FDR) data confirmed the following: Right rudder pedal motion was restricted to approximately 3 degrees, Left rudder pedal motion was not restricted and Centering capability was not restricted. See the attached Illustrations for additional information.
737NG-FTD-25-15004
Rudder Pedal Motion Restricted
Background
An operator reported that a Rejected Take Off (RTO) was performed at 25 knots after pilot experienced stuck rudder pedals. The airplane returned to the gate safely and the flight crew reported no rudder pedal anomalies prior to takeoff roll. Maintenance found a loose flush-head fastener protruding/interfering with the rudder pedal movement (captains rudder pedal housing, left foot - inboard side). Maintenance subsequently re-torqued the fastener, performed a rudder pedal adjustment and limit test with no findings. A Boeing review of Flight Data Recorder (FDR) data confirmed the following: Right rudder pedal motion was restricted to approximately 3 degrees, Left rudder pedal motion was not restricted and Centering capability was not restricted. See the attached Illustrations for additional information.
Originally Posted by lemme @ 2nd Jan 2017, 20:59
Until 60 knots, there should be considerable scrutiny on setting takeoff power. With the data suggesting this speed was never achieved, then the pilot monitoring should have had full attention on the engine instruments, and should have noted reverser deployment without any delay. I would have expected both throttles to be slammed to idle in this occurrence, in less than three seconds to allow for reaction, and engines spooled down about three seconds later.
While an uncommanded deployment would likely be a 10^-9 occurrence, the exercise was intended to reinforce the importance of keeping one's eyes on the engine instruments when setting power and during the entire takeoff run.
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But why would the thrust not be reduced immediately? In low speed reject even application of reverse on the available engine is airbus procedure to swing the aircraft back to the live engine side. Also there is recorded runway excursion due to sitting too far back being unable to apply differential braking. Instantaneous rudder application and thrust levers all the way back to reverse is the correct procedure.
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Waiting eagerly for proper findings on the DGCA enquiry..
Indeed. Here is another incident where the operating crew survived unscathed, as did the a/c; so the subsequent enquiry should be short and swift. All this speculation about what might or might not have happened, or what the crew might have experienced or actioned etc., surely much of that is already known.
Indeed. Here is another incident where the operating crew survived unscathed, as did the a/c; so the subsequent enquiry should be short and swift. All this speculation about what might or might not have happened, or what the crew might have experienced or actioned etc., surely much of that is already known.
Hello vilas; Re,
If the engine went into reverse, yes, exactly.
Whether the engine actually went into reverse or not and if so, by what means, is still not known, so, apropos RAT_5's and others' comments, still awaiting the DGCAs account of events.
Originally Posted by vilas 4th Jan 2017, 11:11
But why would the thrust not be reduced immediately?
Whether the engine actually went into reverse or not and if so, by what means, is still not known, so, apropos RAT_5's and others' comments, still awaiting the DGCAs account of events.
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I have to say, that I do not keep my eyes on the engine instruments during the entire takeoff run. And I don't think that it is a good idea to do so.
While an uncommanded deployment would likely be a 10^-9 occurrence,
With WOW and only two barriers the historical data would suggest something more like 10^-7 but coupled with some redundancy in the aircraft a catatrasphic result would be more like 10^-8
and some would even challenge that a third barrier could meet that 10E-9
With WOW and only two barriers the historical data would suggest something more like 10^-7 but coupled with some redundancy in the aircraft a catatrosphic result would be more like 10^-8 (WOW switch is third barrier)
Of course in this case no catastrophe resulted
JammedStab, re:
Yes, the statement taken literally and without the filters that normally attend knowledge, experience & airmanship is indeed too narrow for advice to young players. I was making the observation expecting that a trained & seasoned airman would know that during takeoff, focus is demanded on all aspects of the takeoff such as aircraft & engine performance, trajectory on the runway, (on centerline), etc. and not just slavishly to the engine gauges without a glance elsewhere.
lomapaseo, re:
Ok, well is it a difference that makes a difference?
The point being made is, it's rare, period, so I should have said "rare" and not applied an exact number.
Originally Posted by JammedStab @ 4th Jan 2017, 17:30
I have to say, that I do not keep my eyes on the engine instruments during the entire takeoff run. And I don't think that it is a good idea to do so.
lomapaseo, re:
Originally Posted by lomapaseo @4th Jan 2017, 17:34
A little too genererous estimated above
The point being made is, it's rare, period, so I should have said "rare" and not applied an exact number.
