Autobrake Settings

[+'ve ROC]

Am I correct in saying that the Autobrake function on a 737NG provides a set rate of deacceleration regardless of reverse thrust / spoilers?

Adding de-acceleration through said sources serves to decrease break wear but will not decrease brake distance. Is this correct?

[TopBunk]

+ROC

I can't comment on the 737NG specifically, but on other types I have flown from Airbus and Boeing that is correct - a programmed deceleration rate dependent on the setting chosen. All by braking if no reverse, braking reduced as a function of the amount of reverse used.

[Flight Detent]

Hi "+'ve ROC",

My understanding is as yours, except that the MAX setting will invoke maximum braking, tempered by antiskid, regardless of any other form of retardation!

Pls feel free to correct if necessary here!

Cheers, FD

[catchup]

@Flight Detent

Agree, that's how the Busses work. About Bill Boeing's toys I don't know.

regards

[ifleeplanes]

Your are correct in that auto brake provides a deceleration rate and will bring the aircraft to a full stop if left to its conclussion. Using reverse thrust spoilers etc in effect reduces the wheel braking since they contribute to the braking force. Autobrake 3 is Max braking BUT it is less than full manual braking. Im on the NG too

[Terraplaneblues]

AB Switch Ft/sec/sec Pressure
1 4 1285
2 5 1500
3 7.2 2000
MAX/RTO 14>80kts 3000
MAX/RTO 12<80kts 3000

But it must be the decel rate which is the master as you state other forms of drag would reduce the pressure one would assume, good question.

PS - have no idea (obviously) how to post tables!

[+'ve ROC]

QUOTE

"Autobrake 3 is Max braking BUT it is less than full manual braking."

So should one choose to use manual brakes, antiskid is inop?

Thanks a lot - you are most helpful!

[ifleeplanes]

If you use manual braking antiskid still operates.

If antiskid is inop autobrake is not available. Loss of antiskid will also give you a huge weight penalty 8500kg and is the worste case in landing distance calculatons for Non Normal ops.

Are you doing an NG rating then?

[+'ve ROC]

No I'm not doing the NG rating, it 's for a piece of academic work on automation and flight.

One more point - does autobrake maintain a deaccel rate regardless of surface conditions? I'm just trying to get this clear in my noggin!

appreciate it

ROC

[XPMorten]

Preset Autobrake decelarion numbers 737.

1 = - 0,124 G's
2 = - 0,155 G's
3 = - 0,224 G's
Max = - 0,37 G / - 0,43 G
RTO = Not controlled

Cheers,

MM

[ifleeplanes]

It will try and maintain a fixed derate however if you are on a surface that is slippery it will be harder for it to do so since the wheels will lock up more easily and the anti skid will be working overtime. However I havnt come across anything so far that causes a problem. We are given braking coefficients if required which we can relate to good or medium or poor braking. We are not allowed to operate if the conditions arein the poor category.

[Niku]

Hi, first post here.

Seeing the standard autobrake deceleration rates for the 737 reminded me of something I have been wondering about. On a dry runway, with anti-skid operative, close to MTOW, what kind of a deceleration rate would you experience on a rejected takeoff using either RTO autobrake or maximum manual braking? Would the rate be very different if the aircraft was very light? How about with full reverse thrust in addition to maximum braking?

Thanks,

Niku