PPRuNe Forums - View Single Post - Do not override autobrake to shorten the landing distance??
Old 20th Nov 2009, 11:14
  #13 (permalink)  
Centaurus
 
Join Date: Jun 2000
Location: Australia
Posts: 4,184
Likes: 0
Received 3 Likes on 3 Posts
Paradoxically, there can be a situation where use of autobrakes can get you into trouble and that is when a directional control problem occurs during a landing roll-out on a slippery runway with a crosswind. The Boeing 737 FCTM gives advice on how to correct a sideways slide when using reverse thrust. It advises the pilot to correct back to the centreline by reducing reverse thrust to reverse idle and release the brakes. In practice this is quite tricky since from full reverse to idle reverse of 23 percent N1 can take as long as 15 seconds to reach a stabilised idle. At the same time a quick stab on the rudder pedals to disengage the autobrakes can cause a further yaw unless the autobrake switch is used to disengage the system.

It could be argued if a strong crosswind is present on a slippery runway it might be worth considering not using autobrake at all but rely on tactile feel of manual rudder pedal pressure to know when to ease off braking in response to unwanted yaw. Boeing go on to say that when re-established on the centre-line apply max braking and symmetrical reverse to stop the aircraft. But you have to keep in mind that it takes several seconds to spool up from idle reverse to full reverse.
Centaurus is offline