A brake wear limit indicator which is matched to the brake energy capacity of the overhauled brake. A wear-limit bushing is attached to the brake piston housing. The bushing length is chosen based on the brake energy capacity of the brake and is marked with a related part number. A wear pin is attached to the brake pressure plate and extends through a hole in the bushing. A brake overhaul is required when the brake wears such that the pin no longer protrudes from the bushing.
Commercial jet aircraft brake stopping performance and brake energy capacity were based on testing conducted on new brakes. Currently, however, the Federal Aviation Administration (FAA) is requiring worn brake accountability on all commercial jet transport category aircraft because there is a degradation in stopping performance and brake energy capacity when steel brakes are worn. As a result of this recent FAA activity relative to worn brake stopping performance, many steel brakes require wear limit adjustments and re-identification of the brake configuration.
It has been standard practice in the past to provide brake part number identification by using raised lettering and/or stamping of the brake piston housing. Wear pins have also been used to indicate when a brake has been fully worn (indicated by a flush wear pin), and should be removed from the aircraft for overhaul. The brake piston housing is a pressure vessel and is under considerable stress during operation. Re-identification by stamping or the attachment of fasteners for the installation of a nameplate introduces undesired stress risers in the brake piston housing.
Therefore, it has been past practice to refrain from re-identification when wear limits are changed. Part number control is required by the FAA-approved Airplane Flight Manual. Because of the concerns associated with re-identification, steel brakes certified for a higher brake energy capacity could not be used at lower brake energy performance values or vice versa.
Indications of brake wear with wear pins referenced to movable brake components are known in the prior art patent literature; as exemplified, e.g., by U.S. Pat. No. 4,658,936 issued Apr. 21, 1987, to Moseley, which contains a wear pin that is held against the pressure plate with spring tension, and wherein the pin is marked to indicate the amount of brake wear by the amount of protrusion from the housing.
Author – WONDESON GETACHEW HAILE
