Thrust reversal

Thrust reverser systems are featured on many jet aircraft to help slow down just after touch-down, reducing wear on the brakes and enabling shorter landing distances.

A landing roll consists of touchdown, bringing the aircraft to taxi speed, and eventually to a complete stop.

However, most commercial jet engines continue to produce thrust in the forward direction, even when idle, acting against the deceleration of the aircraft.

In scenarios involving bad weather, where factors like snow or rain on the runway reduce the effectiveness of the brakes, and in emergencies like rejected takeoffs,[3] this need is more pronounced.

In the original implementation of this system on the Boeing 707,[10] and still common today, two reverser buckets were hinged so when deployed they block the rearward flow of the exhaust and redirect it with a forward component.

[6] Internal thrust reversers use deflector doors inside the engine shroud to redirect airflow through openings in the side of the nacelle.

[4] Engines such as the A320 and A340 versions of the CFM56 direct the airflow forward with a pivoting-door reverser similar to the internal clamshell used in some turbojets.

On selection, the system folds the doors to block off the cold stream final nozzle and redirect this airflow to the cascade vanes.

[6] In cold-stream reversers, the exhaust from the combustion chamber continues to generate forward thrust, making this design less effective.

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.

[citation needed] The Douglas DC-8 series of airliners has been certified for in-flight reverse thrust since service entry in 1959.

[citation needed] The Boeing C-17 Globemaster III is one of the few modern aircraft that uses reverse thrust in flight.

For aircraft susceptible to such an occurrence, pilots must take care to achieve a firm position on the ground before applying reverse thrust.

[2] If applied before the nose-wheel is in contact with the ground, there is a chance of asymmetric deployment causing an uncontrollable yaw towards the side of higher thrust, as steering the aircraft with the nose wheel is the only way to maintain control of the direction of travel in this situation.

[1] Reverse thrust mode is used only for a fraction of aircraft operating time but affects it greatly in terms of design, weight, maintenance, performance, and cost.

Penalties are significant but necessary since it provides stopping force for added safety margins, directional control during landing rolls, and aids in rejected take-offs and ground operations on contaminated runways where normal braking effectiveness is diminished.

Airlines consider thrust reverser systems a vital part of reaching a maximum level of aircraft operating safety.

An Airbus A380 deploying thurst reverser while landing, blowing water from the wet surface and making the reversed air flow observable.
Half-deployed target-type reverser of a RB.199 engine for the Panavia Tornado , one of very few fighter aircraft with thrust reversal
Variable-pitch propellers of an Grumman E-2C Hawkeye
A target-type thrust reverser being deployed on a Cessna Citation.
Target 'bucket' thrust reverser deployed on the Rolls Royce Tay engines of a Fokker 100
Clamshell outlet grating open (outboard engine) on a Rolls-Royce Conway turbofan of a Royal Air Force Vickers VC-10 tanker
Clamshell-type thrust reversers deployed on the Rolls-Royce Trent 700 engine of an Airbus A330 . The redirected thrust blows water from the wet surface, making the air flow observable.
Cold-stream type thrust reverser being deployed on a Boeing 777-300
Reverse thrust levers forward of the main levers, seen on a Boeing 747-8
A vortex made visible as powerback is used on a Boeing C-17 Globemaster III
An American Airlines Boeing 737-800 thrust-reversing on a wet runway.