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Revision as of 13:05, 30 June 2008 by Editor1 (talk | contribs)
Article Information
Category: Flight Technical Flight Technical
Content source: Skybrary skybrary
Content control: Eurocontrol Eurocontrol

Definition

A brake is a device for slowing or stopping the motion of a machine or vehicle, or restraining it from starting to move again.

Description

Aircraft brakes are located on the main wheels and are usually applied by either a hand control or by foot pedals (toe or heel), although on modern aircraft, automated braking systems are also becoming prevalent. Wheel brakes operate independently in order to allow for differential braking, which can supplement nosewheel/tailwheel steering during ground operations. The kinetic energy lost by slowing an aircraft down is usually translated into heat by friction. Anti-Skid or Anti-Lock Braking Systems (ABS) are designed to minimise the amount skidding that occurs when a wheel is stopped from rotating ie locked, thus minimising the potential for tyre damage.

Effects

  • Overheated brakes
    • Loss of braking performance
    • Fire
    • Tyre deflation
  • Brake failure
    • Runway excursions
    • Uncommanded aircraft ground movements

Defences

Minimise brake applications by adjusting power settings when possible, including the use of reverse thrust.

If heavy braking has to be undertaken, ensure an adequate cooling period follows, otherwise subsequent braking performance may be degraded, along with the potential for tyre overheating to occur.

Leave the gear down for protracted periods if overheating is suspected. Know how the brake system operates; each system will have specific instructions associated with it.

Stay aware for uncommanded ground movements; don’t become too engrossed inside the cockpit when on the ground.

Typical Scenarios

The following are extracts from real-life incidents:

  • After landing the aircraft did not decelerating normally and the FO announced ‘Manual Braking’. The commander pressed the brakes without effect. The crew then... The commander braked to bring the aircraft to a halt about 40 metres from the end of the runway, bursting three mainwheel tyres. Analysis showed that it took ten to thirteen seconds for the commander to recognise the lack of pedal braking and there was no overt warning from the ...
  • Shortly after commencing the taxi for takeoff, a hydraulic union in the braking system fractured, causing fluid to leak from the Yellow hydraulic system. The departure was cancelled and the aircraft returned to the terminal. After stopping on the allocated stand, the parking brake was selected on, but the brakes failed to apply, as the parking brake is operated by the Yellow hydraulic system. The aircraft then began to move forward under idle engine power... The aircraft collided with the airbridge, damaging the left engine inlet cowl, before coming to a stop.
  • Having carried out the normal pre-flight checks the pilot released the parking brake by fully depressing the brake pedals prior to taxi. The aircraft was taxied to the threshold of Runway 05, a distance of nearly 2 nm, which took approximately 10 minutes. During this time the engine was running at 1000-1200 rpm and the brakes were rarely operated. Just before arriving at the holding point the pilot noticed "dust - like" smoke coming from the area of the left wheel, the volume of which rapidly increased as the aircraft was brought to a halt.
  • After starting the engine, the aircraft began to move forward. Despite repeatedly operating the toe brakes, the aircraft swung round, resulting in its left wing contacting the left wing of an adjacent aircraft, and its right wing striking the wall of a shed.

Contributory Factors

  • Over-reliance on automated systems which subsequently fail.
  • There is evidence that the fitting of ABS brakes to cars has had an undesirable effect in that drivers have started to drive far more aggressively, believing that they are now much safer. It could be considered not unreasonable to assume that the same psyche may pervade the cockpit.
  • Misunderstanding of the abilities of a braking system; ABS can actually INCREASE the braking distance under some circumstances eg ice, snow, gravel and “soft” surfaces.
  • ABS does not prevent aquaplaning.
  • Spats and leg fairings (which are particularly prevalent on GA aircraft) can lead to poor brake cooling and act as traps for material which can act as a source of ignition for fires.


Solutions

If it is known that the brakes (and tyres) may be hot then the following precautions may be prudent in order to allow the components time to cool:

  • Leave the gear down for a protracted period after take-off.
  • If at all possible, avoid committing to a landing very soon after take-off.
  • Follow the Flight Manual guidelines on cooling periods for example after an emergency stop at whatever speed.

Consider whether Hot Brake incidents should be attended by fire crews.

Ground controllers should consider where they would place an aircraft that requires a prolonged cooling period on the ground so as to minimise disruption to other traffic.

Related Articles

Further Reading

  • [Automatic Braking System Failure