Sequence of Events
On 29 June 2017 at about 1524LT, a B777-300 (registration 9V-SYF) operated by Singapore Airlines landed on Runway 20C at Singapore Changi Airport. After landing, the Runway Controller (RWC) instructed the B777 to vacate via Rapid Exit Taxiway E6 and South Cross 1 (SC1) and contact the Ground Movement Controller (GMC) on frequency 124.3 MHz. The RWC also instructed a departing A320 to line up on Runway 20C.
The RWC observed the B777 vacating the runway and moving on E6. Assessing that the aircraft would soon be clear of the runway holding position marking, he issued a departure clearance to the A320 and cleared an A330 to line up behind it.
As the B777 approached the holding position on E6, the Pilot Monitoring (PM) called the GMC reporting, "Good afternoon, vacated runway for South Cross 1 (SC1)." The Pilot Flying (PF) used the tiller to turn onto SC1 but felt the aircraft was not responding. Applying more tiller input caused the aircraft to turn more than desired. Sensing loss of steering control, the PF stopped the aircraft on E6, with the nose pointing roughly toward the Control Tower.
The flight crew informed the GMC of a technical problem and stated they would hold position. At about 1525LT, the GMC made a general broadcast in the Control Tower alerting controllers. The Tower Watch Manager (WM) heard the broadcast, alerted the Airport Emergency Service (AES), and called aerodrome maintenance crew to assist. The WM quickly assessed that the aircraft appeared clear of the holding position marking.
Meanwhile, the departing A320 had already commenced its take-off roll. The RWC observed this and allowed the A320 to continue, assessing sufficient separation. The A320 departed at about 1526LT, and the A330 began lining up. The RWC advised the A330 of a delay, then consulted the WM, who again assessed the B777 as clear of the runway. The WM used binoculars and noted that the nose and main landing gears had crossed the marking, with parts obscured by wing shadow, but concluded the entire aircraft was clear. The RWC then cleared the A330 for take-off at about 1528LT.
While the A330 was rolling, the WM moved closer to the window and looked again through binoculars. As a precaution, he suspended runway operations on Runway 20C after the A330 departure and requested a ground maintenance vehicle (Rover 39, R39) to check for fluid leaks and confirm if the entire aircraft had crossed the holding position.
R39 arrived at E6 about 1534LT and reported no fluid leak but that the tail end of the B777 was not clear of the runway holding position marking. Runway operations on Runway 20C were suspended until the B777 was towed clear.
Personnel Information
The B777 crew comprised a 60-year-old Commander (PM) with 7853.5 total flying hours (2825.7 on B777) and a 46-year-old First Officer (PF) with 2963.3 total hours (all on B777). The Watch Manager (WM) was 47, licensed since 1994 with 23 years' aerodrome controller experience. The Runway Controller (RWC) was 28, licensed since 2016 with 12 months' experience. The Ground Movement Controller (GMC) was 28, licensed since November 2016 with 8 months' experience.
Meteorological Information
Weather at the time was clear and the ground was dry.
Recorded Data
The investigation accessed air traffic control audio transcripts, recordings of the Airfield Ground Lighting Control and Monitoring System, and closed-circuit TV recordings of the E6 area.
Aircraft Information
The B777-300 has a length of about 74m, a nose-to-main-gear distance of about 31m, and a wingspan of about 61m. A functional test of the nose landing gear system found the nose gear steering metering valve faulty.
Aerodrome Information
The Control Tower height is about 81m above ground, with an unobstructed view of E6. The line-of-sight angle to the B777 at E6 was about 3° from horizontal. The distance from Runway 20C centerline to the E6 runway holding position marking is 145m. Minimum distances for large aircraft (B777, A330, A320) are 90m; for larger types (B747, A380) it is 107.5m.
Analysis
The investigation examined flight crew reporting, the RWC's decision to allow departures while the B777 remained on E6, the WM's judgment of clearance, and air traffic service provider guidelines. The B777 crew had no intention to stop on E6.