Over the years of Boeing 737 simulator training with crews from various airlines we see quite a few variations in use of reverse for landing. .
The FCTM states in part: "Maintain reverse thrust as required, up to maximum until the airspeed approaches 60 knots. At this point start reducing the reverse thrust so that the reverse thrust levers are moving down at a rate commensurate with the deceleration rate of the airplane. The thrust levers should be positioned to reverse idle by taxi speed. Then to full down after the engines have decelerated to idle"
In the simulator it is common to see the PF either cancelling reverse thrust by lowering the reverse levers all the way down at the call of 60 knots (instead of stopping at the reverse idle detent) or, in attempting to locate the reverse idle detent by feel, the PF lowers the reverse levers too far and it becomes forward thrust (not desirable for obvious reasons).
Some pilots deliberately choose to cancel full reverse at the call of 60 knots by smartly placing the reverse thrust levers all the way down. When that happens the N1 takes time to wind down from full reverse. It is during the wind down period the N1 will be rapidly passing through around 60% N1 as the reverse sleeves fully close, leaving the engine momentarily passing a figure of around 55% to 60% N1 in forward thrust. (again undesirable for obvious reasons). Instead of slowing up, the aircraft then momentarily accelerates along the runway due to relatively high N1 in forward thrust on the way down to idle N1
For various reasons, occasionally the PNF fails to call "60 Knots." Usually something else has taken his attention or because he is staring outside the windscreen. In the absence of the "60 knot" call from the other pilot, the PF should start reducing to idle reverse based on his own ASI reading and not relying on a call-out from the PNF to remind him what to do. Surely this is nothing more than a matter of good airmanship and knowledge of the Boeing FCTM published procedures?
Finally, a word about use of reverse thrust for landing on slippery runway operations with a significant crosswind component. Readers can study the appropriate Boeing FCTM advice at their leisure. But read it carefully especially the advice on reverse idle selection and use of brakes. Some operators prefer to have the PNF operating the reverse levers on all landings - dry or slippery. This relies heavily on accurate directions from the PF to the PNF at a dynamic time. If the aircraft starts sliding sideways on a slippery runway then it is vital the PF take over operation of the reverse levers. Some juggling of brakes in conjunction with reverse thrust will be needed and there is no time to call out instructions to the PNF.
Read the diagram published in the FCTM to see what I mean.
Last edited by Centaurus; 31st Jan 2020 at 07:31.