auto brakes rto question
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Joined: Apr 2008
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From: nowhere
auto brakes rto question
Perhaps the answer is obvious but....
After performing an RTO to a complete stop using autobrakes RTO only and allowing them to stop the aircraft, is it correct to say that you have the equivalent of the parking brake being applied until the Autobrakes are deselected?
After performing an RTO to a complete stop using autobrakes RTO only and allowing them to stop the aircraft, is it correct to say that you have the equivalent of the parking brake being applied until the Autobrakes are deselected?
Joined: Mar 2000
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From: Long ago and far away ......
"Equivalent" might be too strong a word to describe this. If you are using the term "parking brake" to help a layman understand what an RTO braking system does, then the analogy may help. But you may also be in danger of confusing someone in to thinking that we try to get airborne with the parking brake on! Obviously, we would never make it in to the air get if we tried that little stunt! 
RTO can be considered as a 'switch' that is set, ready to automatically apply maximum braking following the decision to discontinue a takeoff, when certain conditions are met. In the Boeing 777, for example, these conditions occur when the Autobrake selector is set to RTO (armed) and:
I hope this helps!
RTO can be considered as a 'switch' that is set, ready to automatically apply maximum braking following the decision to discontinue a takeoff, when certain conditions are met. In the Boeing 777, for example, these conditions occur when the Autobrake selector is set to RTO (armed) and:
- the aircraft is on the ground
- groundspeed is above 85 knots, and
- both thrust levers are retarded to idle.
I hope this helps!
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From: N5109.2W10.5
is it correct to say that you have the equivalent of the parking brake being applied until the Autobrakes are deselected?
But if you mean, your procedure after RTO is to set the parking brake - then no they are not equivalent.
Imagine the fire crews inspecting your aircraft without the parking brake set, and someone disarms the ground spoilers.
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From: fairly close to the colonial capitol
There are a few differences, JS, between setting the parking brake and an RTO Autobrake application.
On the 737, the parking brake applies less than 1000psi at the wheels - this figure is not to be confused with hydraulic accumulator pressure. For an RTO, full braking pressure is applied at 3000psi with no modulation for deceleration scheduling - it is the maximum possible. In an RTO event, up to five times the energy is absorbed by the brakes compared to a normal idle-reverse landing.
As Mr. B. indicates above, anti-skid is active for RTO braking but not with the parking brake applied.
On the 737, the parking brake applies less than 1000psi at the wheels - this figure is not to be confused with hydraulic accumulator pressure. For an RTO, full braking pressure is applied at 3000psi with no modulation for deceleration scheduling - it is the maximum possible. In an RTO event, up to five times the energy is absorbed by the brakes compared to a normal idle-reverse landing.
As Mr. B. indicates above, anti-skid is active for RTO braking but not with the parking brake applied.
Thread Starter
Joined: Apr 2008
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From: nowhere
Thanks for the answers.
Remember that the question is not about the deceleration process in which RTO is used. I am talking about once the aircraft has come to a complete stop without any manual braking applied.
Are the brakes still being continuously applied by the Autobrake RTO system and therefore preventing you from taxiing when thrust is applied?
There is a statement to consider not setting the parking brake after a high speed rejected takeoff. But if we let Autobrake RTO stop the aircraft completely, is the aircraft at that point sitting there with brakes fully applied.
Remember that the question is not about the deceleration process in which RTO is used. I am talking about once the aircraft has come to a complete stop without any manual braking applied.
Are the brakes still being continuously applied by the Autobrake RTO system and therefore preventing you from taxiing when thrust is applied?
There is a statement to consider not setting the parking brake after a high speed rejected takeoff. But if we let Autobrake RTO stop the aircraft completely, is the aircraft at that point sitting there with brakes fully applied.
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From: fairly close to the colonial capitol
Are the brakes still being continuously applied by the Autobrake RTO system and therefore preventing you from taxiing when thrust is applied?
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From: N5109.2W10.5
When the aircraft has stopped the wheels are seen as not spinning so therefore brakes would be released by the anti-skid system.
Anti-skid system will deactivate below a given speed.
