The spoilers are panels on the wings that come up during landings to dump lift, which helps to increase the efficiency of braking. They also increase the drag on the aircraft, which helps in aerodynamic braking.
The spoiler panels, when they are extended in flight, act as speed brakes which helps to increase the rate of descent of the aircraft. They can also be deflected differentially, to roll the aircraft.
The types of spoilers on aircraft
There are two main types of spoilers. They are ground spoilers and flight spoilers. The ground spoilers are only used on the ground, while the flight spoilers are used both on the ground and in flight.
To give you an example, the Boeing 737 has 12 spoiler surfaces, out of which only four are dedicated ground spoilers. The rest of the eight spoilers are flight spoilers. In the Airbus A320, there are a total of 10 spoiler surfaces. Out of the 10, only two spoilers are dedicated ground spoilers.
Photo: Boeing 737 FCOM
In the air, the flight spoilers can be used as both speed brakes and roll spoilers.
How spoilers work
The actuation of spoilers or speed brakes in flight causes a reduction in the lift on the wings, which makes the aircraft descend at a faster rate. They come in handy in emergencies that require a very high rate of descent. They can also be used by pilots to manage their descent profiles.
When airplanes descend, they convert potential energy (height) to kinetic energy (speed). What this means is that as an aircraft descends faster and faster, there is an inevitable increase in speed. If a pilot wants to increase his or her descent rate while keeping speed at a low value (this can happen due to restrictions on speed imposed by air traffic control), he or she could extend the spoilers.
By doing so, there is a sudden loss of lift which increases the rate of descent and, at the same time, the drag from the spoiler panels help to reduce the speed of the aircraft.
When used in roll, spoilers are known as roll spoilers. The roll spoilers deflect differentially, which helps to bank the aircraft. For instance, if the pilots want to bank or roll the aircraft to the right, the spoilers on the right wing extend while the spoilers on the left wing remain retracted. This causes the right wing to lose lift, and the aircraft banks to the right.
Photo: Getty Images
During landing and in the event of a rejected takeoff, the spoilers can be extended on the ground to dump lift which increases the load on the wheels. This makes the wheel brakes more effective. When actuated on the ground, both the ground and flight spoilers extend.
Photo: Airbus
There are also airplanes with air brakes. Typically, air brakes are found in the tail of the aircraft, and they do not directly affect the lift of the aircraft. They are purely used to increase the drag on the aircraft, which in turn reduces its speed. They can be extended and used during the approach and all the way to the landing.
There are two commonly known airplanes with this feature. One is the BAe 146, and the other is the Fokker 100.
How are spoilers controlled and operated
In the co*ckpit, the spoilers can be extended or retracted by a spoiler control lever. In most co*ckpit settings, the pilots are required to move the spoiler lever aft to extend them and to move the lever forward to retract them.
When in flight, the movement of the lever only extends the flight spoilers, while the ground spoilers remain locked. When used as speed brakes, the spoilers extend symmetrically on both wings. To give you an example, in the A320, spoilers 2,3, and 4 act as speed brakes. Thus, when the pilot extends them by moving the spoiler lever back, the spoiler panels number 2, 3, and 4 of both the left and the right wing go up.
In some aircraft, if a spoiler surface on one wing fails to extend, the same spoiler on the other wing is automatically inhibited. This is to prevent a spoiler asymmetry condition which could deteriorate the handling characteristics of the aircraft.
Photo: Airbus A380 FCOM
The roll spoilers are automatically activated with pilot inputs on the yoke or the side stick. In non-fly-by-wire aircraft, the roll control is divided. One pilot’s control column controls the aileron, which is the primary control for the roll, and the other pilot’s control column controls the roll spoilers. In most conventional aircraft, both the controls are interconnected such that input in either control column moves both the aileron and the spoilers.
However, when there is a jam in the controls, the force applied to one of the controls releases the interconnection and allows the non-jammed side to control the aircraft. For example, if the ailerons are connected to the captain’s controls and become jammed, the force applied to the first officer’s control removes the connection and allows the first officer to control the roll through the spoiler surfaces.
In the Boeing 737, for example, the captain's yoke is connected to the ailerons, while the first officer's is connected to the roll spoilers.
Photo: Joe Kunzler | Simple Flying
In normal operations, the movement of the aileron control mechanism moves the spoilers. There is a mechanical link between the aileron control rods and the spoiler controls. When a certain amount of control wheel rotation is applied, the spoilers come up together with ailerons which helps to increase the roll rate of the aircraft.
In fly-by-wire aircraft, the spoilers are commanded by the flight control computers.
Spoiler automation
When coming in for a landing or to prepare the aircraft for a rejected take-off, the spoilers can be armed to be automatically extended. To arm the spoilers, the pilots are required to move the spoiler control lever to the arm position. When armed, spoilers come up when certain aircraft conditions are met. Different aircraft manufacturers have different conditions, but in most cases, it involves the detection of the aircraft being on the ground. This detection is done by the Weight on Wheels (WoW) switches which activate when the main landing gears touch down.
Photo: Boeing 737 FCOM
If the pilots forget to arm the spoilers for landing, then there is an automatic spoiler extension mechanism. This usually includes activation of reverse thrust on the engines, and sometimes it comes up automatically when wheels spin up to a certain speed during landing.
In Airbus aircraft, there is a feature called Phased Lift Dumping (PLD). In most Airbus aircraft, the spoilers extend only when both main wheels touch the ground. However, when PLD is active, there is a partial spoiler extension when just one main landing gear makes contact on the runway. This allows for a smoother touchdown of the other main landing gear.
As soon as the other main landing gear touches down, full spoiler extension is commanded. In the Airbus A380, full spoiler extension occurs when three main landing wheels make contact with the runway.
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Photo: Airbus
The spoiler automatic inhibition
The spoilers are automatically retracted if the thrust levers are advanced. This can occur if a pilot were to initiate a go-around after the main wheels touch down. This allows the aircraft to perform during the go-around without losing lift.
In modern aircraft, if the pilot were to move the thrust levers to the max in flight with the spoiler control lever not retracted, the spoilers automatically retract. This inhibition will continue until the pilot moves the thrust levers away from the maximum position and resets the spoiler control lever. Also, some aircraft inhibit speed brakes or reduce their maximum deflection angle with a certain amount of flaps extended. This prevents excessive aerodynamic buffeting on the flaps.
