Sxmarbury33 From United States of America, joined Oct 2000, 445 posts, RR: 0 Posted (12 years 9 months 2 weeks 5 days 19 hours ago) and read 1378 times:
I read somewhere that the autobrakes are tied into the IRU to give a constant deceleration rate. I dont quite see the benefit of having this unless the aircraft is heavy coming in and has to do a quick turn. In this senario the pilot can use heavy reverse and less brake so that they dont heat up affecting the rto performance. Other than that i see no reason. Lets say im taking a 757 into KSNA and using autobrake 3. Im going to want all the brakeforce of auto 3 plus any bouns that the reverse can give me. Im just assuming that this system cuts out in the event that max auto or especially RTO is used. Even though the pilot can always elect to maunually brake i just dont understand the logic of the system so if any of you have opinions or info please post.
HAL From United States of America, joined Jan 2002, 2585 posts, RR: 52
Reply 2, posted (12 years 9 months 2 weeks 5 days 14 hours ago) and read 1350 times:
The autobrake setting is a TOTAL deceleration force. If you have a short runway and elect to use autobrakes 3, the brakes will modulate off as more reverse is used to keep a steady deceleration force. That way you know about how long your landing roll will be, and not be subject to vagaries like uneven pedal application, or delayed reverser application.
One smooth landing is skill. Two in a row is luck. Three in a row and someone is lying.
FDXmech From United States of America, joined Mar 2000, 3251 posts, RR: 33
Reply 3, posted (12 years 9 months 2 weeks 5 days 7 hours ago) and read 1331 times:
A large part of the reason is the autobrake system depends on a properly functioning antiskid system.
Should the antiskid system fail, the autobrake will not arm or will disarm.
One of the parameters the antiskid system requires is a valid IRS input.
Prior to the IRS interfacing with the antiskid system, aircraft speed and deceleration signals were a function solely of wheel speed transducers in each wheel assembly sending its RPM to the A/S computer.
The problem with this is should the wheels stop spinning due to severe hydroplaning or severe runway ice, the computer might think the aircraft stopped moving.
With the IRS coupled to the antiskid and thus autobrake, these systems aren't solely dependant on the spinning wheels for spinup/speed/decelleration signals.
As a sidenote, the A300-600 uses nosewheel speed sensors for its antiskid reference speed, as well as the IRS.