What happened
On the early morning of 24 October 1998, a Boeing 747-136, registration G-AWNN, was operating a scheduled flight from Philadelphia to London Heathrow. Due to heavy headwinds over the Atlantic, the crew diverted to Shannon Airport to refuel.
During the landing on Runway 24, the aircraft's No. 2 engine experienced a surge while the crew was utilizing reverse thrust. Following established procedures, the Flight Engineer shut down the engine to manage a rapid rise in Turbine Gas Temperature. After coming to a halt near the intersection of Runway 24 and Taxiway Alpha, the crew attempted to execute a left-hand turn to exit the runway.
During this maneuver, the aircraft's nose wheels drifted off the paved surface and into the grass verge, striking a taxiway light. The aircraft eventually came to a stop with its nose wheels embedded in the grass. There were no injuries among the 290 passengers or 18 crew members on board.
The investigation
The AAIU examined the mechanical and operational factors surrounding the incident. Investigators focused on the engine surge, the functionality of the aircraft's steering systems, and the crew's decision-making regarding the turn radius.
Technical analysis of the No. 2 engine revealed that a pivot bolt in the Reverse Actuated Bleed System (RABS) had migrated within the engine cowling, which disturbed airflow and triggered the surge. Regarding the steering, investigators found that the circuit breaker for the body gear steering had tripped, which prevented the supplemental steering from assisting the turn. While the crew noted difficulty distinguishing the paved edges from the lighting configuration in the night-time conditions, the investigation confirmed that the runway and taxiway lights were positioned according to standard recommendations.
Findings
- The primary cause of the engine surge was the migration of the RABS cam pivot bolt within the thrust reverser bleed valve.
- The aircraft was unable to complete the intended turn within the available pavement because the body gear steering was inoperative due to a tripped circuit breaker.
- The crew's attempt to execute a 180-degree turn at the runway/taxiway intersection was risky given the nighttime conditions and prevailing winds.
- The Flight Engineer followed correct procedures by shutting down the engine following the temperature spike.