What happened
On 17 May 1998, a Socata TB10, registration G-BHER, completed a series of local flights around Redhill Aerodrome before returning to Biggin Hill Airport. Following a standard landing, the pilot taxied the aircraft via a grass taxiway to a parking area. After the engine was shut down and the pilot had begun post-flight procedures, a strong, acromatised smell of smoke was detected.
Upon inspecting the aircraft, the pilot observed smoke and subsequent flames emerging from the front of the right main landing gear tyre. The fire, which was initially difficult to suppress because it was contained within the wheel spat, was eventually extinguished by the Airfield Fire Service. The incident resulted in no fatalities or injuries, but the aircraft sustained substantial damage, including the destruction of the right-hand fibreglass wheel spat, damage to the hydraulic brake hose, and melting of the lower wing skin.
The investigation
Investigators examined the aircraft and the parking brake system, which utilized a cable-operated mechanism. The maintenance organization noted that this specific system was prone to sticking due to the difficulty of balancing the cables to ensure both pedals released cleanly. Additionally, the physical layout of the cable runs made it difficult to manually release the mechanism if it became stuck.
At the time of the accident, the pilot noted that the parking brake switch was unserviceable, though there had been no signs of brake binding during recent flights. While an instructor suggested that dried grass from the taxiway might have ignited on the hot brake disc, the AAIB also considered the possibility of hydraulic fluid ignition. The investigation noted that the enclosed environment of the wheel spat could allow hydraulic fluid to mix with oxygen and ignite if it came into contact with a hot surface.
Findings
- The fire caused substantial damage to the right wing and right landing gear leg.
- The parking brake system was known to be difficult to balance and prone to sticking.
- The exact cause of the fire could not be definitively established due to the extensive damage to the brake unit and wheel assembly.
- Potential ignition sources included dried grass contacting a hot brake disc or the spontaneous ignition of leaking hydraulic fluid on a hot surface within the wheel spat.