Thrust reversal

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Thrust reversers deployed on the CFM56 engine of an Airbus A321 F-GTAR Air France (3698209485).jpg
Thrust reversers deployed on the CFM56 engine of an Airbus A321

Thrust reversal, also called reverse thrust, is the temporary diversion of an aircraft engine's thrust so that it acts against the forward travel of the aircraft, providing deceleration. 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. Such devices affect the aircraft significantly and are considered important for safe operations by airlines. There have been accidents involving thrust reversal systems, including fatal ones.


Reverse thrust is also available on many propeller-driven aircraft through reversing the controllable-pitch propellers to a negative angle. The equivalent concept for a ship is called astern propulsion.

Principle and uses

Half-deployed target-type reverser of a RB.199 engine for the Panavia Tornado, one of a very few fighter aircraft with thrust reversal Rolls Royce RB.199 2.jpg
Half-deployed target-type reverser of a RB.199 engine for the Panavia Tornado, one of a very few fighter aircraft with thrust reversal

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. [1] The brakes of the landing gear of most modern aircraft are sufficient in normal circumstances to stop the aircraft by themselves, but for safety purposes, and to reduce the stress on the brakes, [2] another deceleration method is needed. 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. [4]

A simple and effective method is to reverse the direction of the exhaust stream of the jet engine and use the power of the engine itself to decelerate. Ideally, the reversed exhaust stream would be directed straight forward. [5] However, for aerodynamic reasons, this is not possible, and a 135° angle is taken, resulting in less effectiveness than would otherwise be possible. Thrust reversal can also be used in flight to reduce airspeed, though this is not common with modern aircraft. [6] There are three common types of thrust reversing systems used on jet engines: the target, clam-shell, and cold stream systems. Some propeller-driven aircraft equipped with variable-pitch propellers can reverse thrust by changing the pitch of their propeller blades. Most commercial jetliners have such devices, and it also has applications in military aviation. [5]

Types of thrust reversal systems

Small aircraft typically do not have thrust reversal systems, except in specialized applications. On the other hand, large aircraft (those weighing more than 12,500 lb) almost always have the ability to reverse thrust. Reciprocating engine, turboprop and jet aircraft can all be designed to include thrust reversal systems.

Propeller-driven aircraft

Variable-pitch propellers of an E-2C Hawkeye US Navy 060403-N-0499M-151 A Sailor performs maintenance to an E-2C Hawkeye.jpg
Variable-pitch propellers of an E-2C Hawkeye
A target-type thrust reverser being deployed
Target 'bucket' thrust reverser deployed on the Tay engines of a Fokker 100 Klm f100 ph-kle arp.jpg
Target 'bucket' thrust reverser deployed on the Tay engines of a Fokker 100

Propeller-driven aircraft generate reverse thrust by changing the angle of their controllable-pitch propellers so that the propellers direct their thrust forward. This reverse thrust feature became available with the development of controllable-pitch propellers, which change the angle of the propeller blades to make efficient use of engine power over a wide range of conditions. Reverse thrust is created when the propeller pitch angle is reduced from fine to negative. This is called the beta position. [7]

Piston-engine aircraft tend not to have reverse thrust, however turboprop aircraft generally do. [8] Examples include the PAC P-750 XSTOL, [9] Cessna 208 Caravan, and Pilatus PC-6 Porter.

One special application of reverse thrust comes in its use on multi-engine seaplanes and flying boats. These aircraft, when landing on water, have no conventional braking method and must rely on slaloming and/or reverse thrust, as well as the drag of the water in order to slow or stop. In addition, reverse thrust is often necessary for maneuvering on the water, where it is used to make tight turns or even propel the aircraft in reverse, maneuvers which may prove necessary for leaving a dock or beach.[ citation needed ]

Jet aircraft

On aircraft using jet engines, thrust reversal is accomplished by causing the jet blast to flow forward. The engine does not run or rotate in reverse; instead, thrust reversing devices are used to block the blast and redirect it forward. High bypass ratio engines usually reverse thrust by changing the direction of only the fan airflow, since the majority of thrust is generated by this section, as opposed to the core. There are three jet engine thrust reversal systems in common use: [6]

Target type

The target thrust reverser uses a pair of hydraulically-operated 'bucket' type doors to reverse the hot gas stream. For forward thrust, these doors form the propelling nozzle of the engine. 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. This type of reverser is visible at the rear of the engine during deployment. [6]

Clam-shell type

The clam-shell door system is pneumatically operated. When activated, the doors rotate to open the ducts and close the normal exit, causing the thrust to be directed forward. [6]

Cascade type

The cascade thrust reverser is commonly used on turbofan engines. On turbojet engines, this system would be less effective than the target system, as the cascade system only makes use of the fan airflow and does not affect the main engine core, which continues to produce forward thrust. [1]

Clam-shell outlet grating open (outboard engine) on a Rolls-Royce Conway turbofan of a VC10 VC10 Aircraft at an Airfield in the Middle East MOD 45150451.jpg
Clam-shell outlet grating open (outboard engine) on a Rolls-Royce Conway turbofan of a VC10

Cold stream type

Pivoting-door thrust reversal seen on the CFM-56 engines of an Airbus A340-300 Airbus A340-313E, Finnair JP7679383.jpg
Pivoting-door thrust reversal seen on the CFM-56 engines of an Airbus A340-300

In addition to the two types used on turbojet and low-bypass turbofan engines, a third type of thrust reverser is found on some high-bypass turbofan engines. Doors in the bypass duct are used to redirect the air that is accelerated by the engine's fan section but does not pass through the combustion chamber (called bypass air) such that it provides reverse thrust. [4] The cold stream reverser system is activated by an air motor. During normal operation, the reverse thrust vanes are blocked. On selection, the system folds the doors to block off the cold stream final nozzle and redirect this airflow to the cascade vanes. [6] This system can redirect both the exhaust flow of the fan and of the core. [5]

The cold stream system is known for structural integrity, reliability, and versatility. During thrust reverser activation, a sleeve mounted around the perimeter of the aircraft engine nacelle moves aft to expose cascade vanes which act to redirect the engine fan flow. This thrust reverser system can be heavy and difficult to integrate into nacelles housing large engines. [11]

Cold-stream type thrust reverser being deployed on a Boeing 777-300. PH-BVC KLM (3701878334).jpg
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 Thrust levers of a Boeing 747-8.jpg
Reverse thrust levers forward of the main levers, seen on a Boeing 747-8

In most cockpit setups, reverse thrust is set when the thrust levers are on idle by pulling them further back. [1] 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'.

The early deceleration provided by reverse thrust can reduce landing roll by a quarter or more. [5] 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.

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. [12]

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.[ citation needed ]

In-flight operation

A vortex made visible as powerback is used on a Boeing C-17 Globemaster III C17 Reverse Thrust.JPG
A vortex made visible as powerback is used on a Boeing C-17 Globemaster III

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.[ citation needed ]

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. [13]

The Hawker Siddeley Trident, a 120- to 180-seat airliner, was capable of descending at up to 10,000 ft/min (3,050 m/min) by use of reverse thrust, though this capability was rarely used.

The Concorde supersonic airliner could use reverse thrust in the air to increase the rate of descent. Only the inboard engines were used, and the engines were placed in reverse idle only in subsonic flight and when the aircraft was below 30,000 ft in altitude. This would increase the rate of descent to around 10,000 ft/min.[ citation needed ]

The Boeing C-17 Globemaster III is one of the few modern aircraft that uses reverse thrust in flight. The Boeing-manufactured aircraft is capable of in-flight deployment of reverse thrust on all four engines to facilitate steep tactical descents up to 15,000 ft/min (4,600 m/min) into combat environments (a descent rate of just over 170 mph, or 274 km/h). The Lockheed C-5 Galaxy, introduced in 1969, also has in-flight reverse capability, although on the inboard engines only. [14]

The Saab 37 Viggen (retired in November 2005) also had the ability to use reverse thrust both before landing, to shorten the needed runway, and taxiing after landing, allowing many Swedish roads to double as wartime runways.

The Shuttle Training Aircraft, a highly modified Grumman Gulfstream II, used reverse thrust in flight to help simulate Space Shuttle aerodynamics so astronauts could practice landings. A similar technique was employed on a modified Tupolev Tu-154 which simulated the Russian Buran space shuttle.[ citation needed ]


The amount of thrust and power generated are proportional to the speed of the aircraft, making reverse thrust more effective at high speeds. [2] [ self-published source? ] For maximum effectiveness, it should be applied quickly after touchdown. [1] If activated at low speeds, foreign object damage is possible. There is some danger of an aircraft with thrust reversers applied momentarily leaving the ground again due to both the effect of the reverse thrust and the nose-up pitch effect from the spoilers. 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. [11]

In-flight deployment of reverse thrust has directly contributed to the crashes of several transport-type aircraft:

See also

Related Research Articles


Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction, to be applied to that system. The force applied on a surface in a direction perpendicular or normal to the surface is also called thrust. Force, and thus thrust, is measured using the International System of Units (SI) in newtons, and represents the amount needed to accelerate 1 kilogram of mass at the rate of 1 meter per second per second. In mechanical engineering, force orthogonal to the main load is referred to as static thrust.

Taxiing Movement of an aircraft on the ground, under its own power

Taxiing is the movement of an aircraft on the ground, under its own power, in contrast to towing or push-back where the aircraft is moved by a tug. The aircraft usually moves on wheels, but the term also includes aircraft with skis or floats.

Landing Transition from being in flight to being on a surface

Landing is the last part of a flight, where a flying animal, aircraft, or spacecraft returns to the ground. When the flying object returns to water, the process is called alighting, although it is commonly called "landing", "touchdown" or "splashdown" as well. A normal aircraft flight would include several parts of flight including taxi, takeoff, climb, cruise, descent and landing.

Spoiler (aeronautics)

In aeronautics, a spoiler is a device which intentionally reduces the lift component of an airfoil in a controlled way. Most often, spoilers are plates on the top surface of a wing that can be extended upward into the airflow to spoil the streamline flow. By so doing, the spoiler creates a controlled stall over the portion of the wing behind it, greatly reducing the lift of that wing section. Spoilers differ from airbrakes in that airbrakes are designed to increase drag without affecting lift, while spoilers reduce lift as well as increasing drag.

Air brake (aeronautics)

In aeronautics, air brakes or speed brakes are a type of flight control surfaces used on an aircraft to increase drag or increase the angle of approach during landing. Air brakes differ from spoilers in that air brakes are designed to increase drag while making little change to lift, whereas spoilers reduce the lift-to-drag ratio and require a higher angle of attack to maintain lift, resulting in a higher stall speed.

American Airlines Flight 625 1976 aviation accident

American Airlines Flight 625, a Boeing 727-100, crashed at St. Thomas, U.S. Virgin Islands on April 27, 1976, while on a domestic scheduled passenger flight originating at T. F. Green Airport in Rhode Island and ending at Saint Thomas, United States Virgin Islands, with an intermediate stop at John F. Kennedy International Airport. 37 out of the 88 passengers on board died in the accident.

Learjet 25

The Learjet 25 is an American ten-seat, twin-engine, high-speed business jet aircraft manufactured by Learjet. It is a stretched version of the Learjet 24.

Qantas Flight 1

Qantas Flight 1 was a Qantas passenger flight between Sydney and London that was involved in a runway overrun accident at Don Mueang International Airport in Bangkok on 23 September 1999 as it was landing for a stopover.

Southwest Airlines Flight 1248

Southwest Airlines Flight 1248 was a scheduled passenger flight from Baltimore, Maryland, to Chicago, Illinois, continuing on to Salt Lake City, Utah, and then to Las Vegas, Nevada. On December 8, 2005, the airplane slid off a runway at Chicago-Midway while landing in a snowstorm and crashed into automobile traffic, killing a six-year-old boy.

Astern propulsion

Astern propulsion is a maneuver in which a ship's propelling mechanism is used to develop thrust in a retrograde direction. Astern propulsion does not necessarily imply the ship is moving astern ; astern propulsion is used to slow a ship by applying a force in the direction of the bow of the ship, instead of the stern. The equivalent concept for an airplane is thrust reversal.

S7 Airlines Flight 778

S7 Airlines Flight 778(RU778/SBI778) was an Airbus A310-300 on a scheduled domestic passenger flight, flying from Moscow Domodedovo to Irkutsk, when it crashed upon landing at Irkutsk International Airport at 07:44 local time on 9 July 2006, killing 125 people. The plane overshot the runway, sliding over several hundred metres of wet runway and grass. It crashed through a concrete barricade, hit a group of private garages and burst into flames. Television pictures showed smoking ruins of the Airbus with only the tail section intact. It took two hours for local firefighters from five different fire stations to extinguish the blaze.

Powered lift

A powered lift aircraft takes offs and lands vertically under engine power but uses a fixed wing for horizontal flight. Like helicopters, these aircraft do not need a long runway to take off and land, but they have a speed and performance similar to standard fixed-wing aircraft in combat or other situations.

TAM Airlines Flight 3054

TAM Airlines Flight 3054 (JJ3054/TAM3054) was a regularly scheduled domestic passenger flight from Porto Alegre to São Paulo, Brazil. On the evening of July 17, 2007, the Airbus A320-233 executing the flight overran runway 35L at São Paulo during moderate rain and crashed into a nearby TAM Express warehouse adjacent to a Shell filling station. The plane exploded on impact, killing all 187 passengers and crew on board and 12 people on the ground. The crash surpassed Gol Transportes Aéreos Flight 1907 as the deadliest aviation accident in Brazilian territory and in South American history, and remains the deadliest aviation accident involving the A320 proper worldwide, and the second-deadliest air disaster involving the A320 family, surpassed by the bombing of Metrojet Flight 9268, an A321-231, which crashed in Egypt in October 2015 with 224 fatalities.

China Airlines Flight 605

China Airlines Flight 605 was a daily non-stop flight departing from Taipei at 6:30 a.m. and arriving at Kai Tak Airport in Hong Kong at 7:00 a.m. local time. On November 4, 1993, the plane went off the runway while landing during a storm. It was the first hull loss of a Boeing 747-400.

RwandAir Flight 205

RwandAir Flight 205 was a Canadair CRJ-100 that crashed into the Terminal Building after an emergency landing at Kigali, Rwanda killing one passenger. The flight was operated by JetLink Express on behalf of RwandAir. In the aftermath of the accident, RwandAir suspended all operations with JetLink Express.

1955 MacArthur Airport United Airlines crash Airplane crash in New York

On April 4, 1955, a United Airlines Douglas DC-6 named Mainliner Idaho crashed shortly after taking off from Long Island MacArthur Airport, in Ronkonkoma, Islip, New York, United States.

Red Wings Airlines Flight 9268

Red Wings Airlines Flight 9268 was a Tupolev Tu-204-100 passenger jet that on 29 December 2012 crashed on landing at Moscow Vnukovo Airport, Russia, following a repositioning flight from Pardubice Airport, Czech Republic. There were no passengers on board, but 5 of the 8 crew members were killed when the aircraft hit a ditch and highway structures after overrunning the runway.

Target-type thrust reversal

Target-type thrust reversal is a deceleration method when an aircraft lands. Like other types of thrust reversals, it temporarily divert the engine exhaust (thrust) forward to provide deceleration. This type of thrust-reverser is suitable for engines of 3,000 lbf (13 kN) or greater thrust.

Sriwijaya Air Flight 62

Sriwijaya Air Flight 62 (SJ62/SSY62) was a scheduled domestic passenger flight, operated by Indonesian airline Sriwijaya Air from Soekarno-Hatta International Airport, Jakarta to Sultan Thaha Airport, Jambi. On 27 August 2008, the aircraft operating the flight, a Boeing 737 series 200 registered as PK-CJG, overran the runway and crashed onto a house during its landing attempt at Jambi. Due to the accident, 26 people were injured, including 3 people on the ground. One person later succumbed to his injuries. Everyone on board the aircraft survived the crash. It was the first fatal crash in Sriwijaya Air's operational history and was the only fatal accident until Sriwijaya Air Flight 182 crashed in 2021.

Air Caraïbes Flight 1501

Air Caraïbes Flight 1501 (TX1501/FWI1501) was a scheduled international passenger flight, flying from Saint Martin Airport in the Dutch overseas territory of Sint Maarten to Saint Barthélemy Airport which was in the French overseas region of Guadeloupe at that time. The flight was operated by Air Caraïbes, a Caribbean regional airline, using a de Havilland Canada DHC-6-300 Twin Otter. On 24 March 2001, during an approach to Saint Barthélemy Airport, the DHC-6 Twin Otter banked steeply to the left and crashed onto a house, killing all 19 passengers and crew on board. One person on the ground was also killed in the explosions that followed.


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