What happened
On 31 May 1998, an Airbus A310-300, registration N835AB, was operating a scheduled passenger flight from Kingston, Jamaica, to London Heathrow. During the flight, the aircraft experienced a failure in the YELLOW hydraulic system caused by a loss of fluid. Following standard procedures, the crew completed the necessary drills and proceeded to land at Heathrow on Runway 27.
After landing, the aircraft taxied to stand M24. Upon reaching the stand, the crew applied the parking brake and brought the aircraft to a halt. However, before chocks could be positioned, the aircraft began moving forward. The pilot attempted to apply maximum braking pressure, but the movement continued until the No 1 engine cowling struck a vertical steel post on the jetway structure. The impact was forceful enough to displace the jetty toward the terminal building and caused damage to the engine cowl. There were no fatalities and no injuries among the 204 passengers or 12 crew members.
The investigation
The investigation examined the aircraft's flight data, cockpit voice recordings, and physical components. Investigators identified that the No 1 engine nose cowling had embedded a rotating beacon and its mounting bracket from the jetty structure.
Technical inspections of the right-hand main gear bay revealed a leak in the YELLOW hydraulic system. The cause was identified as a failed 'O' ring seal in a sampling valve. While the aircraft's braking system was found to be functioning according to its design, investigators noted that the pressure in the brake accumulators had likely depleted. Because the parking brake was applied while the system was unpressurised, the accumulators were not sufficiently charged to hold the aircraft against the residual engine thrust.
Findings
- A failed 'O' ring in a YELLOW hydraulic system sampling valve caused a loss of fluid.
- The loss of hydraulic fluid occurred several hours before the aircraft arrived at the gate.
- Insufficient pressure remained in the brake accumulators to maintain the parking brake's effectiveness against the aircraft's idle thrust.
- There was no specific instruction in the checklists to recharge the accumulators before parking the aircraft after such a failure.
- The parking brake may not have been released by the crew once the movement began, which would have allowed the use of the foot brakes to stop the aircraft.