<P> In most cockpit setups, reverse thrust is set when the thrust levers are on idle by pulling them further back . Reverse thrust is typically applied immediately after touchdown, often along with spoilers, to improve deceleration early in the landing roll when residual aerodynamic lift and high speed limit the effectiveness of the brakes located on the landing gear . Reverse thrust is always selected manually, either using levers attached to the thrust levers or moving the thrust levers into a reverse thrust' gate' . </P> <P> The early deceleration provided by reverse thrust can reduce landing roll by a quarter or more . Regulations dictate, however, that an aircraft must be able to land on a runway without the use of thrust reversal in order to be certified to land there as part of scheduled airline service . </P> <P> Once the aircraft's speed has slowed, reverse thrust is shut down to prevent the reversed airflow from throwing debris in front of the engine intakes where it can be ingested, causing foreign object damage . If circumstances require it, reverse thrust can be used all the way to a stop, or even to provide thrust to push the aircraft backward, though aircraft tugs or towbars are more commonly used for that purpose . When reverse thrust is used to push an aircraft back from the gate, the maneuver is called a powerback . Some manufacturers warn against the use of this procedure during icy conditions as using reverse thrust on snow - or slush - covered ground can cause slush, water, and runway deicers to become airborne and adhere to wing surfaces . </P> <P> If the full power of reverse thrust is not desirable, thrust reverse can be operated with the throttle set at less than full power, even down to idle power, which reduces stress and wear on engine components . Reverse thrust is sometimes selected on idling engines to eliminate residual thrust, in particular in icy or slick conditions, or when the engines' jet blast could cause damage . </P>

Engines using cold stream or both cold and hot stream reversing include