History of the Flight
On 2 December 2011 at about 4:15 p.m., a Boeing 747-400F freighter aircraft operated by Singapore Airlines Cargo, registration 9V-SFL, was landing on Runway 02L at Singapore Changi Airport. The runway was damp, and the aircraft was configured with flaps at 25° and auto-brakes set to level 2. The First Officer (FO) was the pilot flying, and the Pilot-In-Command (PIC) was monitoring.
The aircraft touched down approximately 120 meters beyond the touchdown marking. Thrust reversers were activated. When the aircraft decelerated to about 99 knots, the FO deactivated the auto-brakes by briefly applying manual brakes. Manual brakes were reapplied about five seconds later, during which the aircraft traveled about 280 meters. Thrust reversers were stowed when speed reached about 68 knots.
As the aircraft neared rapid exit taxiway W4, the FO observed a speed of around 60 knots and felt the aircraft was still decelerating (FDR data indicated about 70 knots). The FO focused on locating taxiway W3, his intended exit. Based on visual cues, he judged the speed safe to turn and applied right rudder pedal input. However, FDR data showed negligible rudder input. When the aircraft did not turn, the FO applied some tiller input. The aircraft began turning right, but both pilots felt it skidding left. They attempted to steer back to the runway centerline. Despite their efforts, the right wing gear, right body gear, and nose gear momentarily left the paved runway onto the grass. The control tower observed the excursion and alerted the Airport Emergency Service (AES). The aircraft returned to the runway centerline, vacated via taxiway W2, and taxied to a stop at the intersection of taxiways V3 and WP, where AES approached. After checking systems with no anomalies, the ground engineer reported mud ingestion into the No. 3 engine. The crew shut down that engine as a precaution and taxied to parking bay 505.
Damage
All wheels except No. 4, and all brake assemblies of the right wing gear and right body gear, were damaged and required replacement. One fan blade in the No. 3 engine was damaged by ingested mud. Additionally, four threshold lights of Runway 20R and two elevated runway edge lights between taxiways W2 and W3 were damaged.
Personnel Information
The PIC, aged 40, held an Airline Transport Pilot Licence issued by CAAS, with a B747-400 rating and 9,095 total flying hours (3,624 on type). The FO, aged 34, also held an ATPL with B747-400 rating and 3,440 total hours (3,173 on type). Both had adequate rest of 18 hours 14 minutes before the flight.
Medical and Pathological Information
After the incident, both pilots underwent medical and toxicological tests, which revealed no abnormalities.
Additional Information
A runway friction test conducted after the incident found the friction coefficient within limits.
The aircraft's nose wheel steering could be controlled via rudder pedals (up to ±7° deflection) or a nose wheel steering tiller (up to ±70° deflection). The tiller had precedence over rudder pedal steering. According to the operator's flight manual, the tiller should be used only at normal taxi speed (normally less than 30 knots), and crews were instructed not to have hands on the tiller above that speed.
Investigation Findings
The investigation concluded that the aircraft did not decelerate to a sufficiently low speed for a safe turn onto taxiway W3. When the tiller was applied at relatively high speed, the aircraft began turning but the inertia caused a skid, resulting in the runway excursion.