During normal operations, reverse thrust is usually discontinued below 60 to 80 knots. My employer directs us to begin stowing the reversers at 80 knots, and have them stowed by 60.
That may be your company procedure because of specific airfield conditions. The Boeing 737 recommended procedure is different to your company procedure. The Flight Crew Training Manual states:
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"After touchdown, with the reverse levers at idle, rapidly raise the reverse thrust levers up and aft to the interlock position, then to number 2 reverse thrust detent. Conditions permitting, limit reverse to the number 2 detent. The PM should monitor engine operating limits and call out any operational limits being approached or exceeded, any thrust reverser failure, or any other abnormalities.
Maintain reverse as required, up to the maximum, until the airspeed approaches 60 knots. At this point start reducing the reverse thrust so that the reverse 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 full down after the engines have decelerated to idle. The PM should call out any indvertent selection of forward thrust as reverse thrust is cancelled. If an engine surges during reverse thrust operation, quickly select reverse idle on both engines".
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Idle forward thrust on the 737-300 is approx 23 percent N1. Idle reverse is the same. If the reverse levers are rapidly selected full down fron the full reverse position the engine will come out of reverse around 62 percent N1 giving significant forward thrust just when you are trying to slow up. Not a good look but a very common habit among some pilots.
Note the Boeing advice is to maintain reverse as desired up to the maximum until the airspeed approaches 60 knots. It is often seen where the PF is not heeding the airspeed during the roll-out and instead relies completely on the PM calling 60 knots. Only then, will the PF start reducing reverse thrust. The 60 knot call is purely a reminder - it is not an action call. You would be surprised the number of pilots under training in the simulator will forget to reduce reverse until the aircraft has stopped simply because the PM may have forgotten to call out 60 knots.
However 60 knots is not an action call because under FCOM Normal Amplified Procedures, Boeing also advise "By 60 knots, start movement of the reverse levers to be at reverese idle by taxi speed". In other words
before reaching 60 knots airspeed reverse should be reduced as above. The operative word is "By" not, "at" 60 knots
Done correctly, the N! should be at idle reverse (23 percent N1, by taxi speed. If the procedure is followed the chances of ingestion are minimal. And Boeing should know.
