Reverse thrust
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Thrust.reverser.fokker70.arp.jpg
Reverse thrust is the temporary diversion of a jet engine's output so that the hot exhaust gases are blown forwards rather than backwards. The resulting thrust force acts against the forward travel of the aircraft. Reverse thrust is used by many jet aircraft to help slow down just after touch-down, thus reducing wear on the brakes and enabling the aircraft to use shorter runways.
Regulations dictate, however, that a plane must be able to land on a runway without the use of reverse thrust in order to be certified to land there.
The application of reverse thrust can be identified by a sudden increase in the volume and pitch of the engines' sound just after touch-down. The reversers are usually clearly visible at the rear of the engines during use.
Frequently landings will use "idle reverse thrust" in which the engines do not actually spool up in reverse, but the reversers are activated. This use of the engines saves fuel as well as aides in noise abatement.
External links
- Reducing Landing Distance (http://www.aerospaceweb.org/question/propulsion/q0181.shtml)