What happened
On 18 March 1999, a Beagle B121 Pup Series 2, registration G-AXJJ, was performing a private flight at Huddersfield (Crosland Moor) Airfield. While backtracking on Runway 2-5, the pilot was initially able to use the toe brakes to stop the aircraft twice to avoid a dog on the airfield. However, as the aircraft gained speed while traveling up the 2.6% incline of the runway, the pilot noticed the brakes were losing effectiveness. Despite attempts to pump the brakes and apply the handbrake, the pilot could not maintain control using only nosewheel steering without risking a departure from the runway edges. To avoid the adjacent quarry or the steep 45-degree slope, the pilot chose to run off the end of the runway at approximately 5 knots. The aircraft descended the slope and came to rest on its right wingtip and propeller. The pilot sustained minor injuries, specifically whiplash and lower back pain, and was able to exit the aircraft without assistance.
The investigation
Investigators examined the braking system, which consisted of original Dunlop brakes. They discovered that hydraulic fluid was leaking from the left brake forward piston area and the reservoir was significantly depleted. Upon disassembly, it was revealed that the forward piston had begun to move out of its housing, and the associated friction pad was missing; it was later recovered from the runway. While the rear piston remained in place, the remaining friction pads were worn down to the metal surface of the backplate.
Further investigation into maintenance records showed the aircraft had flown 17 hours since its last 50-hour inspection. The certifying engineer had assessed the brakes as being approximately one-third worn and deemed replacement unnecessary. However, the investigation found that the dimensional checks required by the Service Manual can be misleading if only certain components of the pad assembly are replaced. Additionally, the maintenance organisation was unfamiliar with this specific aircraft type and had not been informed of the unusually high rate of brake pad wear experienced by this aircraft due to its operating environment.