Originally Posted by
LarryJ
That would require a double failure, though, wouldn't it?
Is reserve braking hydraulic or pneumatic?
On the DC9/MD80 half of the cylinders on each brake are on the right system and half on the left. Losing one system doesn't affect your ability to brake.
Alternate brakes are on the left side, normal and reserve braking is on the right. Reserve braking is accomplished through a standpipe using trapped fluid in the reservoir. I don't have a QRH with me but I believe it tells you that if you lose normal braking to arm the reserve brakes in the event the alternate brakes fail (hence my thought process with the brakes).
Also, with alternate brakes, anti-skid works differently in that it is per wheel pair vs per wheel with normal braking.