What happened
On 29 June 2017, a runway incursion occurred at Changi Airport involving a Singapore Airlines Boeing B777-300, registration 9V-SYF, and two departing aircraft. After landing on Runway 20C, the B777-300 attempted to vacate the runway via Rapid Exit Taxiway E6. During the turn, the pilot encountered a technical issue where the aircraft's nose landing gear steering metering valve failed, causing the aircraft to lose steering control. Consequently, the aircraft stopped on E6, positioned such that its tail remained behind the runway holding position marking.
While the B7/77-300 was stationary, the Runway Controller cleared an A320 to line up and take off. Shortly after, an A330 was also cleared to line up and depart. Although the aircraft was not at immediate risk of collision due to sufficient separation, the presence of the 9V-SYF on the taxiway constituted an incursion.
The investigation
Investigators examined the sequence of events, the controllers' decision-making processes, and the technical failure of the aircraft. The investigation established that the flight crew had reported the runway as vacated in anticipation of crossing the holding position, rather than after the aircraft had fully cleared it.
At the Control Tower, the Watch Manager performed multiple visual checks, including the use of binoculars, to assess the position of the 9V-SYF. However, the aircraft's orientation—with its nose pointing toward the tower—and shadows cast by the wings obscured the view of the holding position markings. It was only when a ground maintenance vehicle, Rover 39, reached the aircraft that it was confirmed the tail end had not yet cleared the marking.
Findings
- The primary cause of the incursion was the failure of the nose landing gear steering metering valve on the B777-300.
- The flight crew reported the runway as vacated before the aircraft had physically crossed the runway holding position marking.
- Visual assessments from the Control Tower were hindered by the aircraft's unusual orientation and shadows cast by the wings.
- There was no risk of collision with the departing A320 or A330 because of the significant safety margin between the holding position on E6 and the runway centerline.
Safety action
Following the incident, the air traffic service provider implemented improvements to the Advanced-Surface Movement Guidance and Control System (ASMGCS) to provide better visual references for separation. Additionally, the airline operator issued a reminder to all pilots to ensure aircraft have completely passed the relevant runway holding position markings before reporting a runway as vacated.