What happened
On 9 July 1998, an Airbus A300-600, registration N70072, was conducting a scheduled passenger flight from London Heathrow to Boston. During the initial climb, the crew observed a persistent 'Oil Filter Clog' caution light for the number two engine. Following established emergency procedures, the crew attempted to clear the indication by adjusting the throttle, but the light remained steady. Consequently, the commander elected to shut down the number two engine.
The aircraft returned to London Heathrow for an emergency landing. Because the aircraft lacked a fuel jettison system, it landed at a weight of 368,000 lb, significantly exceeding the normal maximum landing weight of 308,700 lb. While the touchdown was smooth, the aircraft's deceleration was heavily influenced by asymmetric forces. As the aircraft rolled to the end of the runway, the crew noted that while the left brake temperatures were normal, the four right-side brake temperatures had reached the maximum gauge reading of 700°C.
Upon stopping, the crew observed smoke emanating from the right main landing gear area. The Airport Fire Service attended the scene and identified a small fire caused by burning grease. The incident resulted in no fatalities and no injuries to the 174 passengers or 11 crew members, though all four tyres on the right gear deflated due to the heat.
The investigation
The investigation focused on two primary areas: the cause of the engine oil filter warning and the overheating of the right-side brakes. Engineers examined the number two engine and found no mechanical damage or actual filter clogging. Instead, they discovered that the differential pressure switch had suffered an internal short circuit due to water contamination.
Regarding the braking issue, investigators analyzed the landing conditions, noting the use of asymmetric reverse thrust on the left engine and the presence of a crosswind. The investigation examined the energy absorption capabilities of the brake system during overweight landings and the impact of differential braking used to maintain directional control.
Findings
- The engine oil filter warning was a spurious indication caused by a short circuit in the pressure switch.
- The right-side brakes absorbed a disproportionate amount of braking energy due to the use of differential braking to counteract yawing moments from the crosswind and asymmetric thrust.
- The aircraft landed significantly above its normal maximum landing weight.
- Excessive lubrication of the wheel bearings may have contributed to the fire, as melted grease from the axles was found on the bogie components.
Safety action
- Airbus Industry was advised to reassess the adequacy of the oil filter clog caution system, particularly for ETOPS operations.
- Guidance for crews regarding aircraft handling during ground rolls with one engine shutdown was recommended for amplification in the Operating Manual.
- A recommendation was made for aviation authorities to review brake system certification requirements, specifically regarding overweight landings and the effects of crosswind and asymmetric thrust.