Airbus Auto Brake system
Join Date: Aug 2001
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Nice one Bolty! You're starting to talk like me!
Hey, I need to correct/clarify my previous missive.
According to the AMM, the deciding factor is NOT MLG WOW, but at least two ground spoilers commanded to extend. That may be parsing things a bit as the ground spoiler command comes from MLG WOW (and well, face it, auto spoilers armed, although that is left out of the AMM text), but hey, we're trying to be technical.
Anyhoo, here's the deal....
A/B LO or MED will apply after a preset delay (don't ask me, they don't specify, it's a "preassigned value") provided there is a command for two ground spoilers.
A/B MAX will apply after a command for at least two ground spoilers <AND> NLG WOW
<OR> (here's the gotcha)
A command for two ground spoilers plus eight (8) seconds.
The choice is either LO or MED and get stopping action from the brakes fairly quick, or select MAX and wait 8 seconds (how much runway behind?) and get either the nose gear dropped like a rock, or you plant the nose gear yourself to get the quick stop. (Your spine, your choice)
I don't know. Unless you have a serious need for it, A/B MAX would not be a good idea at the end of the day.
Any scenario, whether manual or auto shouldn't cause you to get seriously overheated brakes unless you were landing on a severely short runway as A/B MAX is nothing more than you stomping on the brakes and saying "I WANT TO STOP RIGHT NOW!!!!
However, the A/B system never panics, it's computer controlled, don't ya know....
PB
Hey, I need to correct/clarify my previous missive.
According to the AMM, the deciding factor is NOT MLG WOW, but at least two ground spoilers commanded to extend. That may be parsing things a bit as the ground spoiler command comes from MLG WOW (and well, face it, auto spoilers armed, although that is left out of the AMM text), but hey, we're trying to be technical.
Anyhoo, here's the deal....
A/B LO or MED will apply after a preset delay (don't ask me, they don't specify, it's a "preassigned value") provided there is a command for two ground spoilers.
A/B MAX will apply after a command for at least two ground spoilers <AND> NLG WOW
<OR> (here's the gotcha)
A command for two ground spoilers plus eight (8) seconds.
The choice is either LO or MED and get stopping action from the brakes fairly quick, or select MAX and wait 8 seconds (how much runway behind?) and get either the nose gear dropped like a rock, or you plant the nose gear yourself to get the quick stop. (Your spine, your choice)
I don't know. Unless you have a serious need for it, A/B MAX would not be a good idea at the end of the day.
Any scenario, whether manual or auto shouldn't cause you to get seriously overheated brakes unless you were landing on a severely short runway as A/B MAX is nothing more than you stomping on the brakes and saying "I WANT TO STOP RIGHT NOW!!!!
However, the A/B system never panics, it's computer controlled, don't ya know....
PB
Join Date: Sep 2000
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Hi Guys,
The answer is that max braking on an Airbus should not be used for landing only the RTO case (I understand third hand Boeing max braking is much less aggressive).
In 1994 Airbus Flight Test Dept. ran a series of braking tests with A340s at MTOW (test pilots running out of things to do I guess).
Three TPs were asked to brake more or less manually (I think they were allowed the benefit of anti skid) at MTOW V1 and try and beat the aircraft with max braking selected in the same conditions. All failed...the max braking selection at MTOW resulted in all plugs blowing on all tyres.
Some interesting result asides
1. Whilst all applied maximum braking initially one immediately backed off as it felt seriously wrong.
2. The other two both tried but failed to hold maximum braking through the entire deceleration. It was found that the left handed pilot allowed the right brake to release earlier and VV for the right handed pilot.
Conclusion was that if they could not do it when they were expecting it us mere line pilots would definately require max auto brake to avoid running off the end. Design guys vindicated...fire service not impressed with having their pool games disrupted.
The answer is that max braking on an Airbus should not be used for landing only the RTO case (I understand third hand Boeing max braking is much less aggressive).
In 1994 Airbus Flight Test Dept. ran a series of braking tests with A340s at MTOW (test pilots running out of things to do I guess).
Three TPs were asked to brake more or less manually (I think they were allowed the benefit of anti skid) at MTOW V1 and try and beat the aircraft with max braking selected in the same conditions. All failed...the max braking selection at MTOW resulted in all plugs blowing on all tyres.
Some interesting result asides
1. Whilst all applied maximum braking initially one immediately backed off as it felt seriously wrong.
2. The other two both tried but failed to hold maximum braking through the entire deceleration. It was found that the left handed pilot allowed the right brake to release earlier and VV for the right handed pilot.
Conclusion was that if they could not do it when they were expecting it us mere line pilots would definately require max auto brake to avoid running off the end. Design guys vindicated...fire service not impressed with having their pool games disrupted.
Join Date: Apr 2003
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Janspeed,
Good to get some empirical evidence. If it feels like "you have hit something" at 72 knots then it is deffo more aggressive than Mr. B's max braking equivalent.
Al the dinosaur said the Airbus view is max auto brake SHOULD not be used for landing (as opposed to MUST not). This gives the crew discretion to use max auto brake in the emergency unfactored performance landing on a short runway.
Both your posts point to an abort at Max TOW (however much heavier that is than max landing weight) at V1 resulting in tyres exceeding fuse temperatures. The higher speed and higher weight do not have a linear relationship and I would be surprised if the energy dissapated by brakes in the MTOW V1 case is not twice that of a relatively slow speed max landing weight. Not Airbus qualified so some numbers would help from those that are.
Good to get some empirical evidence. If it feels like "you have hit something" at 72 knots then it is deffo more aggressive than Mr. B's max braking equivalent.
Al the dinosaur said the Airbus view is max auto brake SHOULD not be used for landing (as opposed to MUST not). This gives the crew discretion to use max auto brake in the emergency unfactored performance landing on a short runway.
Both your posts point to an abort at Max TOW (however much heavier that is than max landing weight) at V1 resulting in tyres exceeding fuse temperatures. The higher speed and higher weight do not have a linear relationship and I would be surprised if the energy dissapated by brakes in the MTOW V1 case is not twice that of a relatively slow speed max landing weight. Not Airbus qualified so some numbers would help from those that are.
Only half a speed-brake
Bus (320) has ABRK: LO/MED/MAX.
Max is the equivalent of full manual (and successful!) braking designed for rejected takeoff. From design point of view, use for landing is off limits.
Oin' (737) has ABRK: RTO - equivalent of full manual (and successful!) braking
and landing modes of 1/2/3/MAX
Max is maximum autobrake setting suggested by design for landing. It is much less then the RTO setting and so it must not be used for takeoff since braking performance is insufficient.
My comment is that you cannot compare MAX(bus) to MAX(boing) as these are two completely different braking modes.
Happy braking.
FD
(the un-real)
Did I mention that I landed with PRK BRK set on Sunday? No, no, that would never happen not even in a sim...
