Aug 31, 2020

1. What is the difference between the reverse thrust detents and are there any visual indications (say N1) to differentiate between them?

2. Are there fixed conditions as to when we would use the various detents, as opposed to saying “we‘ll use max reverse thrust on this landing as we have a quick turnaround time and need to keep the brakes cool”?

I understand that there is idle reverse, normal reverse and maximum reverse. On other forums there have been suggestions that typical respective N1 values are circa 40%, 70% and 80% but cannot find this published anywhere.

1 answer1 reply

Hi Steve, Rather than visual differences, there are tactile one when you select the reversers. Idle detent is at the reverser interlock 2nd detent can be selected once the reverser deploys and interlock unlocks Maximum reverse is past the 2nd detent (you can feel the 2nd detent as it gives you friction and you need to apply a bit of force to get past the detent) As to which one to use:

  • FCTM - "Conditions permitting, limit reverse thrust to the number 2 detent"

  • But also to minimize brake cooling FCTM "select maximum reverse thrust as soon as possible after main gear touchdown. Do not wait for nose wheel touchdown. The intention is to use reverse thrust as the major force that stops the airplane. The use of maximum reverse thrust further minimizes brake heating"

  • Brake cooling schedule is based on 2nd detent reverse, there is no data for maximum reverse thrust. This means that you cannot take credit for it. 2nd detent is normally more than enough even for 25 min turnaround.

  • On the line (this can differ from company to company):

  • You would use idle reverse if you can (brake cooling, not performance limited runway) to save fuel

  • If not then 2nd detent

  • You would use maximum reverse during RTO or short performance limited or slippery runway to ensure shortest stopping distance

  • As to the N1 values, these are roughly correct. Idle reverse is 40% only for 2 (SFP) or 5 seconds after touch down. It then drops to 20% when the EECs switch to ground idle