RTO in a boeing?
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RTO in a boeing?
What is the procedure for rejecting a takeoff before THR HOLD? Is it possible to close the thrust levers against the servos or will the A/T disconnect when they are retarded?
If you close the throttles at low speed, with the autobrakes set to RTO, will you still get maximum braking? If so, isn't this a bit extreme for an aircraft that maybe only doing 40kts?
If you close the throttles at low speed, with the autobrakes set to RTO, will you still get maximum braking? If so, isn't this a bit extreme for an aircraft that maybe only doing 40kts?
G'day TB,
The thrust levers can be closed against servo pressure but the auto throttle has to be disconnected before THR HLD or else the thrust levers will re-advance to take off thrust.
The autobrake RTO function becomes active at 85 knots so low speed RTOs are fairly sedate.
This info is in relation to a B767-300.
Regards,
BH.
The thrust levers can be closed against servo pressure but the auto throttle has to be disconnected before THR HLD or else the thrust levers will re-advance to take off thrust.
The autobrake RTO function becomes active at 85 knots so low speed RTOs are fairly sedate.
This info is in relation to a B767-300.
Regards,
BH.
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I can answer your question relative to our operations and airplane, but you'll get differing replies. We don't use autothrottles for takeoff, so autothrottle isn't a consideration when rejecting a takeoff.
That said, one is always able to override thrust levers or the autopilot. Additionally, when retarding the thrust levers one can disconnect the autopilot via palm switches on the inboard thrust levers.
RTO brakes, as part of the autobrake system, must be armed by positioning the cockpit switch to ON, but must also be armed by the wheels sensing a minimum speed. In our case, we must be moving at least 80 knots for activation of the RTO autobrakes, with no antiskid faults, and any symmetrical set of thrust levers moved to the reverse interlock position. Application of manual brakes disarms the system, just like landing autobrakes.
Some of the later systems in the type I'm presently flying use 85 knots and all thrust levers to idle, rather than requiring the reverse interlock on two symmetrical thrust levers, to activate RTO brakes...but all the criteria must still be met. Too low a speed, an anti skid fault, thrust levers not retarded, any manual braking, the RTO switch not ON, or any autobrake faults detected will individually or collectively disarm the RTO brakes and prevent them from activating.
To answer your second question, then, one won't get takeoff autobrakes (and maximum braking) at 40 knots, because the airplane isn't traveling fast enough to arm the autobrake system.
The RTO switch doesn't actually arm the system. It really disarms the system, when in the OFF position. When in the ON position, it gives the system permission to arm when all the necessary criteria are met, including those cited above.
When activated, RTO brakes deliver the full 3,000 psi braking pressure to the wheels with just enough antiskid bypass to prevent a wheel lockup.
That said, one is always able to override thrust levers or the autopilot. Additionally, when retarding the thrust levers one can disconnect the autopilot via palm switches on the inboard thrust levers.
RTO brakes, as part of the autobrake system, must be armed by positioning the cockpit switch to ON, but must also be armed by the wheels sensing a minimum speed. In our case, we must be moving at least 80 knots for activation of the RTO autobrakes, with no antiskid faults, and any symmetrical set of thrust levers moved to the reverse interlock position. Application of manual brakes disarms the system, just like landing autobrakes.
Some of the later systems in the type I'm presently flying use 85 knots and all thrust levers to idle, rather than requiring the reverse interlock on two symmetrical thrust levers, to activate RTO brakes...but all the criteria must still be met. Too low a speed, an anti skid fault, thrust levers not retarded, any manual braking, the RTO switch not ON, or any autobrake faults detected will individually or collectively disarm the RTO brakes and prevent them from activating.
To answer your second question, then, one won't get takeoff autobrakes (and maximum braking) at 40 knots, because the airplane isn't traveling fast enough to arm the autobrake system.
The RTO switch doesn't actually arm the system. It really disarms the system, when in the OFF position. When in the ON position, it gives the system permission to arm when all the necessary criteria are met, including those cited above.
When activated, RTO brakes deliver the full 3,000 psi braking pressure to the wheels with just enough antiskid bypass to prevent a wheel lockup.
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I just found this video filmed from the cabin of a 757 during an RTO. From what was said it appeared to be a birdstrike. It's amazing how quickly the aircraft returns to taxi speed after the "pop". 
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Where the picture was taken from a passenger window, it's really hard to comment regarding taxi speed, or the speed at which the RTO took place...looking out the window is really just subjective guesswork.
Here's a RTO demo of the 777 during certification:
YouTube - Boeing 777 rejected take off (RTO)
Here's a RTO demo of the 777 during certification:
YouTube - Boeing 777 rejected take off (RTO)
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(737-800 ops) Question 1: The procedure is the same both for low speed and high speed. Close thrust levers, disengage A/T, monitor RTO or max manual, speedbrakes, max reverse. In that order. Before 84 kts and THR HLD, you'll have to disconnect the A/T because if you don't they will move towards T/O N1.
Question 2: Yes, you can move the thrust levers against the servos without them disengaging. They will not disconnect when retarded.
Question 3: No, it's only armed above 90 kts.
The Boeing Flight Crew Training Manual (type specific) contains some very interresting charts of the different reject scenarios, no reverse, no speedbrake, late deployment etc. There's a very good reason to do the drill in excactly as the book says.
Another notion. I'm beginning to have second thoughts about the assumed temp procedure (reducing T/O power on long RWs to reduce wear&tear). If you always go max derate, you're always operating on the limit for the Stop case when RW limited. Which means, in the event of a reject, you'll have to perform as the Boeing test pilots did. Also, on the 737-800, in cross wind it seems that we get alot of tail strikes. My opinion is, that to keep the aircraft level during rotation, you have to apply so much control wheel deflection that the speedbrakes extend, and thus reducing alot of lift, and this at the stage where you have a pitch moment of 3 degrees pr sec.
My advice is, keep it simple, don't let the SOP's blind you and use common sense. No one will ever fire you because you went full T/O thrust, but if you go off the end after using max derate....you'll be in a pile of ****e.
Question 2: Yes, you can move the thrust levers against the servos without them disengaging. They will not disconnect when retarded.
Question 3: No, it's only armed above 90 kts.
The Boeing Flight Crew Training Manual (type specific) contains some very interresting charts of the different reject scenarios, no reverse, no speedbrake, late deployment etc. There's a very good reason to do the drill in excactly as the book says.
Another notion. I'm beginning to have second thoughts about the assumed temp procedure (reducing T/O power on long RWs to reduce wear&tear). If you always go max derate, you're always operating on the limit for the Stop case when RW limited. Which means, in the event of a reject, you'll have to perform as the Boeing test pilots did. Also, on the 737-800, in cross wind it seems that we get alot of tail strikes. My opinion is, that to keep the aircraft level during rotation, you have to apply so much control wheel deflection that the speedbrakes extend, and thus reducing alot of lift, and this at the stage where you have a pitch moment of 3 degrees pr sec.
My advice is, keep it simple, don't let the SOP's blind you and use common sense. No one will ever fire you because you went full T/O thrust, but if you go off the end after using max derate....you'll be in a pile of ****e.
