What happened
On 30 January 2003, an Airbus A340-311, registration G-VSKY, was taxiing at London Heathrow Airport for a scheduled flight to Newark. While maneuvering to line up on Runway 27R, the aircraft began to slide on a surface contaminated with ice and snow. The crew, operating at a speed of approximately 3 to 6 kt, attempted to correct the slide by applying asymmetric thrust to the right-hand engines. However, the combination of the slippery surface and a strong norace wind caused the right main landing gear to leave the paved taxiway and sink approximately 50 centimetres into the soft grass.
Following the excursion, the aircraft settled into a right-wing-low attitude, prompting the crew to shut down the right-hand engines. There were no fatalities and no injuries among the 14 crew members or the 130 passengers on board. The disembarkation of passengers was delayed for approximately two and a half hours while de-icing equipment was deployed to clear the taxiway.
The investigation
Investigators analyzed data from the quick access recorder, which confirmed the commander's account of the aircraft's movement and the brief application of power to the right engines. The investigation also reviewed meteorological records, noting that while the runway had been de-iced, the taxiway surfaces were contaminated.
Examination of ground operations revealed that while the runway and high-speed exits were prioritized for de-icing, there was no formal requirement at the time to measure or assess the friction levels of taxiway surfaces. The investigation noted that the last recorded de-icing of the taxiway had occurred several hours prior to the incident, and the heavy snow being blown across the area by the wind had likely re-contaminated the surface.
Findings
- The primary cause of the excursion was the contaminated taxiway surface consisting of ice and snow.
- The aircraft was maneuvering at a low speed, and the application of asymmetric thrust was insufficient to arrest the slide.
- There was no established requirement or procedure to assess or report friction conditions on taxiway surfaces.
- The presence of a strong northerly wind contributed to the sliding motion and the accumulation of new snow on the taxiway.