Brakes are fitted to an Aircraft for the following reasons.
- To enable the Kinetic energy of the moving aircraft to be converted into heat through the medium of friction, so reducing the forward motion of the aircraft during a landing run.
- To permit the aircraft to be steered while taxying on the ground.
- To restrict the forward speed when taxying, residual thrust from the engine often being appreciable.
- To hold the aircraft stationary against full thrust when the engines are run up for testing purposes.
- To enable the aircraft to be parked safely.
The brake unit must be light, have good retardation effects, and must be able to dissipate the heat generated whist retarding the aircraft. There are several types in use, and they can be placed in the following groups.
- Shoe – for light aircraft
- Drum – for light aircraft
- Disc, predominantly used on modern aircraft.
Maintenance.
Contamination of the friction surfaces of a brake unit by fluids used in aircraft servicing operations is highly detrimental to brake operation. It is essential therefore, to protect brakes from contamination by fuel, oil, grease, paint remover, de-icing fluid, etc., when operations involving their use are undertaken and the condition of the brake units should subsequently be confirmed by inspection. Installed disc brakes may be inspected for signs of fluid leakage, external damage, corrosion, disc pack wear and overheating, and the associated hydraulic pipes for security, distortion, chafing or leaks. Brake disc pack wear can be checked by measuring wear pin protrusion, the limits being specified in the approved Maintenance Manual.
In some installations a worn disc pack may be exchanged after removing the wheel and thrust or back plate, and without disconnecting the hydraulic system, but in order to carryout a detailed inspection the brake unit must be removed from the axle.
At the periods specified in the approved Maintenance Schedule the brake unit should be removed for inspection and overhaul. The wheel should first be removed and the hydraulic pipe couplings should be disconnected at the brake and fitted with suitable blanks. In some cases fluid will drain from these pipes and bleeding will be necessary
after re-connection, but in other cases connection is by self sealing couplings which isolate the hydraulic system from the brake unit. The brake unit attachment bolts should then be removed and the unit carefully withdrawn.