<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> <P> Some aircraft, notably some Russian and Soviet aircraft, are able to safely use reverse thrust in flight, though the majority of these are propeller - driven . Many commercial aircraft, however, cannot . In - flight use of reverse thrust has several advantages . It allows for rapid deceleration, enabling quick changes of speed . It also prevents the speed build - up normally associated with steep dives, allowing for rapid loss of altitude, which can be especially useful in hostile environments such as combat zones, and when making steep approaches to land . </P> <P> The Douglas DC - 8 series of airliners has been certified for in - flight reverse thrust since service entry in 1959 . Safe and effective for facilitating quick descents at acceptable speeds, it nonetheless produced significant aircraft buffeting, so actual use was less common on passenger flights and more common on cargo and ferry flights, where passenger comfort is not a concern . </P>

The purpose of cascade vanes in a thrust reversing system is to