What happened
On 2 December 2011, a Singapore Airlines Cargo Boeing 747-400F, registration 9V-SFL, was landing on Runway 02L at Singapore Changi Airport. The flight, arriving from Sharjah, UAE, touched down on a damp runway. During the landing roll, the First Officer deactivated the auto-brakes at approximately 99 knots by briefly applying manual brakes, but did not maintain this braking pressure for several seconds.
As the aircraft approached rapid exit taxiway W3, the flight crew attempted to turn the aircraft toward the exit. During this maneuver, the aircraft's right wing gear, right body gear, and nose gear momentarily left the paved surface and entered the grass area. The crew managed to steer the aircraft back onto the runway and proceed to a parking bay. The incident caused damage to various wheels, brake assemblies, and runway lighting, and mud was ingested into the No. 3 engine, damaging a fan blade.
The investigation
The investigation focused on the deceleration process and the mechanics of the turn. Investigators found that the First Officer had deactivated the auto-brakes earlier than usual to expedite the runway vacancy, based on a visual perception that the aircraft was at a safe speed. However, the investigation revealed that the pilot had not checked the actual airspeed immediately before the turn attempt.
Furthermore, the investigation examined the use of the nose wheel steering tiller. While the pilot used the tiller to initiate the turn, the aircraft was traveling at approximately 59 knots, which is significantly higher than the typical taxi speed of under 30 knots for which tiller use is recommended.
Findings
- The aircraft failed to decelerate to a sufficiently low speed before attempting to vacate via taxiway W3.
- The flight crew deactivated the auto-brakes prematurely and did not maintain manual braking, which prevented the aircraft from reaching a safer turning speed.
- The use of the nose wheel steering tiller at a high speed (59 knots) caused the aircraft's inertia to trigger a skid, leading to the excursion.
- The pilot relied on visual cues rather than instrument readings to judge the aircraft's speed during the turn.