Spoiler (aeronautics)

A close look at the inner workings of spoilers in lift dump deployment during the landing of anAirbus A320.

A close look at the spoiler (the parts of the wing that are raised up) during the landing of anAirbus A321.

A view of the right wing of aBoeing 767-300ERduring descent with spoilers partially deployed.

Spoilers deployed to slow down for descent on a QantasBoeing 737-800.

Extended spoilers are intended to increase thelift-induced dragby spoiling thespanwiselift distribution across the wing. The glider shown is aSlingsby Capstan.

Inaeronautics,aspoiler(sometimes called alift spoilerorlift dumper) is a device which intentionally reduces theliftcomponent of anairfoilin a controlled way. Most often, spoilers are plates on the top surface of a wing that can be extended upward into the airflow tospoilthe streamline flow. By so doing, the spoiler creates a controlledstallover the portion of the wing behind it, greatly reducing the lift of that wing section. Spoilers differ fromairbrakesin that airbrakes are designed to increase drag without disrupting the lift distribution across the wing span, while spoilers disrupt the lift distribution as well as increasing drag.

Spoilers fall into two categories: those that are deployed at controlled angles during flight to increase descent rate or control roll, and those that are fully deployed immediately on landing to greatly reduce lift ( "lift dumpers" ) and increase drag. In modern fly-by-wire aircraft, the same set of control surfaces serve both functions.

Spoilers were used by mostgliders(sailplanes) until the 1960s to control their rate of descent and thus achieve a controlled landing. Since then, spoilers on gliders have almost entirely been replaced by airbrakes, usually of theSchempp-Hirthtype. Spoilers and airbrakes enable the glide angle to be altered during the approach while leaving the speed unchanged.

Airlinersare almost always fitted with spoilers. Spoilers are used to increase descent rate without increasing speed. Their use is often limited, however, as the turbulent airflow that develops behind them causes noise and vibration, which may cause discomfort to passengers. Spoilers may also be differentially operated for roll control instead ofailerons;Martin Aircraft was the first company to develop such spoilers in 1948.Onlanding,however, the spoilers are nearly always fully deployed to help slow the aircraft. The increase inform dragcreated by the spoilers directly assists the braking effect. However, the most gain comes as the spoilers cause a dramatic loss of lift and hence the weight of the aircraft is transferred from the wings to the undercarriage, allowing the wheels to be mechanically braked with less tendency to skid.

In air-cooledpiston engineaircraft, spoilers may be needed to avoidshock coolingthe engines. In a descent without spoilers, air speed is increased and the engine will be at low power, producing less heat than normal. The engine may cool too rapidly, resulting in stuck valves, cracked cylinders or other problems. Spoilers alleviate the situation by allowing the aircraft to descend at a desired rate while letting the engine run at a power setting that keeps it from cooling too quickly (especially true forturbochargedpiston engines, which generate higher temperatures thannormally aspiratedengines).

Spoiler controls

Spoiler controls can be used for roll control (outboard or mid-span spoilers) or descent control (inboard spoilers).

Some aircraft use spoilers in combination with or in lieu ofaileronsfor roll control, primarily to reduceadverse yawwhen rudder input is limited by higher speeds. For such spoilers the termspoileronhas been coined. In the case of a spoileron, in order for it to be used as a control surface, it is raised on one wing only, thus decreasing lift and increasing drag, causing roll and yaw. Eliminating dedicated ailerons also avoids the problem ofcontrol reversaland allowsflapsto occupy a greater portion of the wing trailing edge.

Almost all modern jet airliners are fitted with inboard lift spoilers which are used together during descent to increase the rate of descent and control speed. Some aircraft use lift spoilers on landing approach to control descent without changing the aircraft's attitude.

One jet airliner not fitted with lift spoilers was theDouglas DC-8which used reverse thrust in flight on the two inboard engines to control descent speed (however the aircraft was fitted with lift dumpers). TheLockheed Tristarwas fitted with a system calledDirect Lift Controlthat used the spoilers on landing approach to control descent.

Airbusaircraft withfly-by-wirecontrol utilise wide-span spoilers for descent control, spoilerons, gust alleviation, and lift dumpers. Especially on landing approach, the full width of spoilers can be seen controlling the aircraft's descent rate and bank.

Lift dumpers

Lift dumpers are a special type of spoiler extending along much of the wing's length and designed to dump as much lift as possible on landing. Lift dumpers have only two positions, deployed and retracted. Lift dumpers have three main functions: putting most of the weight of the aircraft on the wheels for maximum braking effect, increasingform drag,and preventing aircraft "bounce" on landing.

Lift dumpers are almost always deployed automatically on touch down. The flight deck control has three positions: off, automatic ( "armed" ), and manual (rarely used). On landing approach "automatic" is selected and, on touchdown, a sensor called a weight-on-wheels switch signals the lift dumpers to be raised. The flight control spoilers are also raised as additional lift dumpers.

Virtually all modern jet aircraft are fitted with lift dumpers. TheBritish Aerospace 146is fitted with particularly wide-span spoilers to generate additional drag and makereverse thrustunnecessary.

A number of accidents have been caused either by inadvertently deploying lift dumpers on landing approach, or forgetting to set them to "automatic".

Incidents and accidents

• Air Canada Flight 621– Premature deployment of the spoilers at low altitude contributed to this crash inTorontoon 5 July 1970.
• United Airlines Flight 553– Forgetting to deactivate the spoilers contributed to crash atChicago Midway International Airporton 8 December 1972.
• LoftleiðirIcelandic Airlines Flight 509 – Deployment of lift dumpers while attempting to arm them 40 feet above the runway caused this accident atJohn F. Kennedy International Airporton 23 June 1973.
• American Airlines Flight 965– Forgetting to deactivate the spoilers while climbing to avoid a mountain contributed to this crash on 20 December 1995.
• American Airlines Flight 1420– Forgetting to deploy the spoilers contributed to this crash atLittle Rock National Airporton 1 June 1999.
• Atlantic Airways Flight 670– The spoilers did not deploy during landing on a fairly short wet runway, causing overrun and falling over a cliff, on 10 October 2006.
• TAM Airlines Flight 3054– ThisAirbus A320's pilots were aware of their deactivated starboard engine #2 thrust reverser,and so apparently did not attempt to use it to brake when attempting to land atSão Paulo's Congonhas Airporton 17 July 2007; under one theory of the cause, they used an old procedure, which reduced the required runway length for landing but was superseded because it invited pilot error, which required them to leave the engine in idle rather than reverse thrust, and mistakenly left the engine at full power.The plane's spoilers may have been their only method of braking at speed. The plane slid off the runway, over a major highway, and ploughed into a warehouse, killing all 186 on board as well as several on the ground. It wasBrazil's worst aviation disaster.

See also

• Air brake (aircraft)