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Old 28th Jul 2007, 20:18
  #614 (permalink)  
bsieker
 
Join Date: Jul 2007
Location: Germany
Posts: 550
A320 autobrake

Originally Posted by PEI_3721
MAX is used for takeoff. Also, when landing in contaminated conditions most aircraft manufacturers require MAX as the normal procedure.
MAX will not provice better deceleration on slippery surfaces than MED.

As has been discussed here, there are three autobrake settings on the A320, LO, MED and MAX.

LO has a target deceleration of 1.7m/s/s, MED of 3.0 m/s/s, and MAX has no such limit and brakes as hard as possible. MAX is only to be used for rejected take-offs.

On slippery surfaces (and I'm not implying anything about the state of the accident runway), 3m/s/s may not be achievable at all, so MED and MAX settings will have the same effect.

If not even 1.7m/s/s can be achieved, LO will provide the same deceleration, but LO autobrake starts 2 seconds later than MED (4s after ground spoiler deployment, vs. 2s in MED), so the total distance will be longer.

This also makes it clear that the thrust reversers do not shorten the braking distance when the friction between wheels and runway can achieve 3m/s/s (or 1.7m/s/s for "LO" autobrake). They just ease some of the strains on the brakes.

To convey that "MAX" is different from LO and MED, its pushbutton is set slightly separated from the other two.

Just getting the physics and autobrake logic straight.
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