What happened
On 11 May 1999, a Fan Jet Falcon 20F, registration G-BGOP, was being prepared for a private flight at Farnborough Airport. After completing initial cockpit preparations, the commander applied the parking brake and, hearing the sound of hydraulic pressure, authorized ground engineers to remove the wheel chocks. Following his external inspections, the commander briefly left the cockpit.
While the aircraft was unattended, the co-pilot noticed the aircraft moving forward. Attempts to engage the emergency brakes were unsuccessful. The co-lag also attempted to start the No 2 and No 1 engines to generate hydraulic power for the braking system, but neither engine responded. As the G-BGOP drifted, it veered to the left and collided with the right wing of a parked Gulfstream 3, registration PK-PJA. The collision caused damage to the Falcon's No 2 engine nacelle, fuselage, and front windscreens, as well as damage to the wing of the Gulfstream.
The investigation
Investigators examined the hydraulic and braking systems of the G-BGOP following the incident. While the hydraulic valves were functioning correctly, the investigation revealed that the parking brake accumulator suffered from an internal leak, which caused a gradual loss of pressure over time.
It was also noted that the aircraft had recently undergone repairs for a generator fault, and the generator switches had been left in the off position, which prevented the engines from being started during the emergency.
Findings
- The primary cause of the movement was the gradual loss of hydraulic pressure in the parking brake accumulator caused by an internal leak.
- The crew was unable to provide hydraulic power for the brakes because the engine start sequence was precluded by the generator switches being left in the off position.
- The flight deck lacks a dedicated brake pressure gauge, meaning the crew had no way to monitor accumulator pressure when the aircraft's electrical power was disconnected.
- The commander's initial confirmation of hydraulic pressure was misleading because the pressure switch for the master fault panel only activates when electrical power is applied to the system.