Jammed Elevator on takeoff B737
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Centaurus
Scratching at fading memories here but isn't the range of the main electric trim on the 737 less than the full range of manual trim wheel inputs, hence full nose down trim will be unrecoverable without manual trim wheel input?
On the subject, if the trim setting is on the forward limit of the green band (so no take of configuration warning upon setting take off thrust) does that guarantee that there is sufficient elevator authority at Vr to initiate rotation?
winding the stab trim fully forward before take off in the simulator. Of course the crew are briefed it is a training exercise with no surprises. The aurul warn C/B is pulled to silence the configuration warning
On the subject, if the trim setting is on the forward limit of the green band (so no take of configuration warning upon setting take off thrust) does that guarantee that there is sufficient elevator authority at Vr to initiate rotation?
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Jammed Elevator on takeoff B 737
Hi Sciolistes, 80 Kts because the elevator becomes responsive then. At the start of the TO roll, you won't know if there is any control surface movement. At 80 kts you will
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Nearly right Port Strobe, the electric trim is forward limited, to move outside this range you have to pull the stab trim cutout switches and wind the stab trim fwd manually. If you restore the stab trim cut outs, the electric trim will be available from the fully fwd position you are now in to wind the stab trim back to the normal range.
Thie exercise ( jammed elevator) was probably introduced as the incorrect technique was applied during the take off roll.
Thie exercise ( jammed elevator) was probably introduced as the incorrect technique was applied during the take off roll.
mis trim/cg v jammed elevator
Hi.
if the elevator control moves full deflection without developing a pitch rate, the likelihood is the aircraft is out of trim, by either an erroneous stabiliser setting, or an incorrect load. For the first case, the aircraft is designed to have adequate elevator authority to override the stabiliser setting. For the erroneous cg, in most cases there is adequate elevator and stabiliser available to fly the aircraft, but rotation will be at a higher speed due to the delay in response.
The cg error can be either excessively forward or aft:
for the aft cg, the aircraft will have a noticeable poor nosewheel steering response at almost all speeds, with a fair bit of scuffing occurring. If that doesn't trigger some concern, on power application on most aircraft (not the MD11/DC10) the nose will pitch up, extreme cases. In all cases the pitch attitude will increase on the roll without command. On one case evaluated, the pitch up occurred on thrust application, and the nose wheel was off the ground before 60 KIAS, and the aircraft lifted off without control input about 5 kts before V1. The aircraft was dynamically unstable, but only mildly so, and the crew engaged the autopilot at low altitude which coped with the instability. In that case the crew then cleaned up.... and continued to destination... and the cg got worse along the way. on landing the aircraft pitched up after touchdown and went off the side of the runway at low speed. That aircraft had a cg 12%MAC aft of the normal envelope, and 2% further aft than ever tested by the manufacturer. The data showed that the AP was responding to the instability constantly during the cruise, and the possibility existed that a disengagement in cruise would have resulted in structural overload through a PIO. Don't recommend flying an out of trim aircraft at speed or high mach, altitude....
On another aft cg case, the aircraft pitched up on thrust application and the tail hit the ground, below 50KIAS. the crew rejected the takeoff, but were able to taxi back...
For the forward cg case, it is only going to be apparent at rotate; on one case evaluated, the elevators moved correctly to their commanded position, but there was no pitch rate initially, with increasing pitch at about Vr+20KIAS with full elevator application. The aircraft cleanup was delayed until the crew confirmed the trim error, and evaluated that the configuration change would not adversely affect the trim case. Normal fuel burn placed the cg shift beneficially, on landing the aircraft used limited flap and full manual trim, and was still out of trim but controllable in pitch.
A jammed elevator is indicated by restricted movement of the elevator control on a conventional control system, and may be either in the control runs or the actuator/surface. Most mechanical systems have a control system split available, where override will disconnect the L & R control channels to allow freedom of movement. FBW systems introduce alternative failure modes, but for the B777 are basically conventional, the Airbus is different....
On a 4 engine aircraft at heavy/limiting weights, a jam noted at Vr is going to be bad news. The time available for evaluation and response is probably less than that available before crossing the golf course.
On a 2 engine aircraft, the situation is a little better, and there may be adequate time to apply nose up trim sufficient to fly the aircraft off the ground. I would think your ball park figure is going to be in the order of 3-4 units of additional ANU trim to get the plane to respond, and that will take some time to run, probably 8-10 seconds. From that time, the aircraft will start to pitch After liftoff, the aircraft will have excessive ANU trim and will continue to pitch up, and will need a return to near the original TO trim position. If the speed gets out of sorts, roll may be advantageous in maintaining speed until the stab trim has been set correctly.
If you have proceeded with a takeoff, and get airborne, then limiting configuration changes may be wise. The aircraft AP system particularly ones with CWS functionality may have the ability to bypass the control run if that is the cause of the jam, and act directly to the elevator hydraulic control servo (at least one type does that).
time wise, the 4 engine aircraft at balance field limit high weights is going off the end of the runway about 12 seconds after Vr... so if it takes some time for the trim to reset (say 8 secs), and then some time to rotate (say 5 secs), it is going to be close... really close (yes attitude will start to change at some point as the trim is being run...). The reject is also going off the end, at around 80-100Kts... dealers choice. The light twins are going to be in better shape for both stop and go cases. Individual case will depend on runway available, weight/thrust etc.
Best place to have this is in a sim, and probably not as an unbriefed event. Before placing any faith in the go case on a 4 engine aircraft, would really want to practice that is a sim to assess runway used. While the sim is not necessarily certified for that evolution, the trim response "should" be close to representative.
The above is some background on the issue, and should not be construed to be a procedure. At the end of the day, the buck stops in the LHS.
Good luck!
if the elevator control moves full deflection without developing a pitch rate, the likelihood is the aircraft is out of trim, by either an erroneous stabiliser setting, or an incorrect load. For the first case, the aircraft is designed to have adequate elevator authority to override the stabiliser setting. For the erroneous cg, in most cases there is adequate elevator and stabiliser available to fly the aircraft, but rotation will be at a higher speed due to the delay in response.
The cg error can be either excessively forward or aft:
for the aft cg, the aircraft will have a noticeable poor nosewheel steering response at almost all speeds, with a fair bit of scuffing occurring. If that doesn't trigger some concern, on power application on most aircraft (not the MD11/DC10) the nose will pitch up, extreme cases. In all cases the pitch attitude will increase on the roll without command. On one case evaluated, the pitch up occurred on thrust application, and the nose wheel was off the ground before 60 KIAS, and the aircraft lifted off without control input about 5 kts before V1. The aircraft was dynamically unstable, but only mildly so, and the crew engaged the autopilot at low altitude which coped with the instability. In that case the crew then cleaned up.... and continued to destination... and the cg got worse along the way. on landing the aircraft pitched up after touchdown and went off the side of the runway at low speed. That aircraft had a cg 12%MAC aft of the normal envelope, and 2% further aft than ever tested by the manufacturer. The data showed that the AP was responding to the instability constantly during the cruise, and the possibility existed that a disengagement in cruise would have resulted in structural overload through a PIO. Don't recommend flying an out of trim aircraft at speed or high mach, altitude....
On another aft cg case, the aircraft pitched up on thrust application and the tail hit the ground, below 50KIAS. the crew rejected the takeoff, but were able to taxi back...
For the forward cg case, it is only going to be apparent at rotate; on one case evaluated, the elevators moved correctly to their commanded position, but there was no pitch rate initially, with increasing pitch at about Vr+20KIAS with full elevator application. The aircraft cleanup was delayed until the crew confirmed the trim error, and evaluated that the configuration change would not adversely affect the trim case. Normal fuel burn placed the cg shift beneficially, on landing the aircraft used limited flap and full manual trim, and was still out of trim but controllable in pitch.
A jammed elevator is indicated by restricted movement of the elevator control on a conventional control system, and may be either in the control runs or the actuator/surface. Most mechanical systems have a control system split available, where override will disconnect the L & R control channels to allow freedom of movement. FBW systems introduce alternative failure modes, but for the B777 are basically conventional, the Airbus is different....
On a 4 engine aircraft at heavy/limiting weights, a jam noted at Vr is going to be bad news. The time available for evaluation and response is probably less than that available before crossing the golf course.
On a 2 engine aircraft, the situation is a little better, and there may be adequate time to apply nose up trim sufficient to fly the aircraft off the ground. I would think your ball park figure is going to be in the order of 3-4 units of additional ANU trim to get the plane to respond, and that will take some time to run, probably 8-10 seconds. From that time, the aircraft will start to pitch After liftoff, the aircraft will have excessive ANU trim and will continue to pitch up, and will need a return to near the original TO trim position. If the speed gets out of sorts, roll may be advantageous in maintaining speed until the stab trim has been set correctly.
If you have proceeded with a takeoff, and get airborne, then limiting configuration changes may be wise. The aircraft AP system particularly ones with CWS functionality may have the ability to bypass the control run if that is the cause of the jam, and act directly to the elevator hydraulic control servo (at least one type does that).
time wise, the 4 engine aircraft at balance field limit high weights is going off the end of the runway about 12 seconds after Vr... so if it takes some time for the trim to reset (say 8 secs), and then some time to rotate (say 5 secs), it is going to be close... really close (yes attitude will start to change at some point as the trim is being run...). The reject is also going off the end, at around 80-100Kts... dealers choice. The light twins are going to be in better shape for both stop and go cases. Individual case will depend on runway available, weight/thrust etc.
Best place to have this is in a sim, and probably not as an unbriefed event. Before placing any faith in the go case on a 4 engine aircraft, would really want to practice that is a sim to assess runway used. While the sim is not necessarily certified for that evolution, the trim response "should" be close to representative.
The above is some background on the issue, and should not be construed to be a procedure. At the end of the day, the buck stops in the LHS.
Good luck!
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Hi yankee, if the control surface wont move then neither will the control wheel - at any speed.
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Even if all four ailerons were jammed the wheel will still move, but it wouldn't do you a lot of good.
L1011, a superior design
Moderator
The aircraft was dynamically unstable, but only mildly so
Probably not ? In general, a knowledgeable pilot (read TP training) might manage to fly a circuit in a statically unstable aircraft but it would be a bit of an ask to expect a successful outcome in a dynamically unstable example.
The tale is a thing of eyebrow raising and heart thumping ... and excessive sweating.
Probably not ? In general, a knowledgeable pilot (read TP training) might manage to fly a circuit in a statically unstable aircraft but it would be a bit of an ask to expect a successful outcome in a dynamically unstable example.
The tale is a thing of eyebrow raising and heart thumping ... and excessive sweating.
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Then again, it might...if any flaps/slats are extended, due differential spoiler actuation with control wheel movement.
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Carl,
737 of course
The answer was in the context of the elevator. But on the 737 the Capt's control wheel controls the ailerons and the FO's the spoilers. Both control wheels are connected thus actuating both types of flight controls accordingly. If a jam on either side is experienced, the opposite side can break the connection and have some roll control.
What type of aircraft?
On the L-1011 if an aileron is jammed, bungees installed in the input system will extend or collapse to allow movement of the control wheel and any un-jammed aileron.
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If a jam on either side is experienced, the opposite side can break the connection and have some roll control.
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Scratching at fading memories here but isn't the range of the main electric trim on the 737 less than the full range of manual trim wheel inputs, hence full nose down trim will be unrecoverable without manual trim wheel input?
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Denti & KG
Thanks for that, makes sense that MET would be allowed to get you out that corner. Taking the flap lever out the UP detent was mighty useful to set full AND trim prior to deicing
Thanks for that, makes sense that MET would be allowed to get you out that corner. Taking the flap lever out the UP detent was mighty useful to set full AND trim prior to deicing
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On the L1011, the handle labeled 'pull roll disconnect' will accomplish the same purpose.
Now, lower the flaps to 4 degrees or more, and do the same procedure above. Now along with the 4 full up ailerons you will get 12 up spoilers, for even more fun.
Both of the above may be a little to much fun to have while you are in the air, so I suggest they only be accomplished on the ground.
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411A, if you want to have a little fun, pull that "roll disconnect handle", then have your co-pilot turn his control wheel full left, at the same time you turn your control wheel full right. All 4 ailerons will move full up.
Now, lower the flaps to 4 degrees or more, and do the same procedure above. Now along with the 4 full up ailerons you will get 12 up spoilers, for even more fun.
Both of the above may be a little to much fun to have while you are in the air, so I suggest they only be accomplished on the ground.
Now, lower the flaps to 4 degrees or more, and do the same procedure above. Now along with the 4 full up ailerons you will get 12 up spoilers, for even more fun.
Both of the above may be a little to much fun to have while you are in the air, so I suggest they only be accomplished on the ground.
We do most of our pilot/FE proficiency checks in the airplane now, since the Bournmouth L10 sim went TU some time ago.
Recall years ago some DC8 pilots were in training on the L10, and they tried some pre-start control checks, with hydraulics...OFF.
Aileron crosshatch lights illuminated, as you might expect, and I was called from hotac at 3am...and asked...'whatever could be wrong?'
My simple reply...'RTFB, dummy, it ain't a Douglas.'
