Originally Posted by
MightyGem
Reverse thrust in flight??
Yes, all four engines can go into reverse thrust in flight. The C-17 also has speed brakes. In speed brake mode the flaps extend to dramatically increase drag, and the spoilers deploy to cancel out the increase in lift caused by the flaps and also further increase drag. This makes possible a tactical descent well in excess of 20,000 ft/min. The idea being to arrive directly over the destination airfield in a combat zone at high altitude and then very rapidly spiral down and land before an enemy outside the airport can drop mortars or other weapons on the runway. It works very well.
And incidentally, besides in flight reverse, the reversers are safe and effective at negative airspeed. Meaning the C-17 can back up on the ground under its own power at max weight, up a 2% slope, into a tail wind. On almost all aircraft you don't want to use the reversers below about 50 knots because of "re-ingestion," where the engines re-ingest exhaust air which can cause severe compressor stalls.