On 30 March 2017, a Boeing 787-9 (9V-OJA) being operated by Scoot was taxiing for departure on a scheduled passenger flight from Singapore in normal night visibility when it was in wingtip-to-wingtip collision with a stationary Airbus A380-861 being operated by Emirates which had just been pushed back from its parking gate for departure. Both wingtips were damaged but the 787 crew were only alerted to the fact that impact was likely to have occurred when they heard the A380 requesting a return to the gate because of damage and, upon confirming by inspection that their aircraft was also damaged, also requested clearance to a parking bay.
An Investigation was carried out by the Singapore Transport Safety Investigation Bureau (TSIB). The 787 EAFRs were downloaded but although relevant parameter data was available, the two hours of voice data did not include taxi out because, contrary to Operator procedures, the EAFRs had not been deactivated once parked. Relevant ATC recorded data were also available.
The 58 year-old Captain of the 787 had 17,000 hours total flying experience but only 314 hours of this was on type. The 35 year-old 787 First Officer had 2,570 hours total flying experience which included 1,270 hours on type. The GND Controller in position was found to have been a 27 year-old trainee being supervised by a 26 year-old OJT Trainer. She had completed 5 months practical training towards the requirements for validation at Changi after beginning her controller career at Seletar aerodrome. The OJT trainer had a total of 4 years five months experience at Changi and she had “deemed” the trainee to be sufficiently competent to “manage traffic independently”.
It was established that after just over half an hour in position, the OJT trainee operating the GND position instructed the 787, which had just completed pushback from gate E28 at Terminal 2 to “taxi on greens” and hold short of Taxiway WA (see the first illustration below). This route involved following taxiways A6 and NC3 but in accordance with ‘follow the greens’ procedures, this was not verbalised. At the time this clearance was given green taxiway centreline lights were illuminated continuously along taxiways A6, NC3 and WA towards the runway 02L threshold (see the second illustration below) and had been so for the past 30 minutes as a number of aircraft had taxied on WA during that time. According to the OJT trainee, she intended to route the 787 onto taxiway WP after an arriving aircraft had landed and vacated Runway 02L via RET W5 at which point she would switch the green taxiway centreline lights leading onto WA off and switch on those leading onto taxiway WP and along it as far as the intersection with taxi lane V6. She had apparently decided that she would be able to reconfigure the lighting in this way before the 787 arrived at the WA/NC3 intersection and “she did not see the need to switch on the red stop bar light on NC3 short of WA”. The 787 crew readback of the clearance was correct and the OJT Trainer stated that she had not seen any reason to intervene.
Almost immediately, the OJT trainee cleared the A380 to pushback from gate C23 at Terminal 1 and this movement, which involved pushing the aircraft tail-first into a south-facing position, commenced about three minutes later (see the third illustration below). Within a minute of this pushback beginning, the 787 crew reported that they were approaching the WA/NC3 intersection and were instructed by the trainee controller to “…continue on the greens and hold short V6”. The trainee and her supervisor then reported having turned their attention to four departing aircraft near the runway 02L holding point. As the 787 approached the WA/NC3 intersection, its crew could see continuous green centreline lights leading from taxiway NC3 onto taxiway WA and that there was a red stop bar on the final part of NC3, so they complied with the instruction to “taxi on greens” and turned left onto taxiway WA. Once the turn was complete, both 787 pilots saw the A380 stationary on taxiway U1 and assessed visually that there was enough clearance between the two aircraft for them to continue taxiing. Even so, the First Officer, who was acting as PF, slowed the aircraft down significantly as they were about to pass the A380s vertical stabiliser. The A380 tug driver reported that he had stopped the push back prior to the collision because he had been unsure if there was sufficient separation between the two aircraft for them to pass safely.
The OJT controllers’ intended taxi route for the 787. [Reproduced from the Official Report]
The lit taxiway centreline whilst the 787 was taxiing showing the illuminated red stop bar at the junction of NC3 and WP. [Reproduced from the Official Report]
The A380 pushback from C23 to face south. [Reproduced from the Official Report]
The left wing of the 787 then contacted the right winglet of the A380 and the tug driver reported having heard a scraping sound. The B787 crew reported having felt only a “slight jerk” and having concluded that they must have taxied over an area of uneven surface had continued taxiing.
About a minute after the collision had occurred, the trainee controller and her supervisor returned their attention to the B787 and saw that it was on taxiway WA rather than the intended taxiway WP and was approaching the WA/VZ intersection. Unaware of anything untoward, the trainee instructed the 787 to taxi to WP via V6 for departure on Runway 02L.The A380 crew then asked to return to their gate after being told of collision wing damage by their tug crew and this was approved. The 787 crew heard this exchange and stopped the aircraft. The Captain then asked the cabin crew to check the left wing visually and received back a report that the left wing navigation light “appeared to be detached and hanging freely” upon which positioning back to a parking bay was requested and a corresponding clearance received.
Damage to the 787 left wing was subsequently found to include several composite panels and damage to the A380 right wing was found to include several skin panels and a number of cracked ribs and spars. There were no injuries to the 822 occupants of the two aircraft.
The Investigation noted that there had been two identical prior events where the aircraft ‘following the greens’ on WA had been stopped before reaching an A380 facing south on taxiway U1 after pushback from C23. One of these events had been recorded two months before the collision under investigation and the other 9 months earlier. Following the January 2017 event, ATC had begun a review of its procedures and requested that the airport operator should review pushback operations but neither review had been completed by the time the collision occurred.
It was noted that the collision could not have occurred if the taxiway lighting had been configured to match the clearance given and considered that “there may be merit in ATC verbalising the taxi route” when ‘follow-the-greens’ clearances were in use. However, the ATC view was that this was not necessarily a good risk management solution. The difficulties of pilots assessing wingtip clearances visually were noted and it was concluded that prudence dictated that an aircraft should be stopped if the potential clearance was in any way marginal. It was noted that in this case, “the ambient lighting, contrast between the brightly lit vertical stabiliser of the A380 and its dark right wing tip and relative position of both aircraft” were all factors that may have affected the accuracy of the 787 pilots’ visual perception.
A number of Safety Actions were noted to have been implemented by various parties following the collision but the Investigation nevertheless determined that it was necessary to make a total of eight Safety Recommendations as follows:
- that the Air Traffic Services Provider considers verbalising the taxi route in addition to the instruction to “taxi on the greens” in the taxi clearance. [RA-2018-004]
- that the Civil Aviation Authority of Singapore considers requiring the Air Traffic Services Provider to verbalise the taxi route in addition to the instruction to “taxi on the greens” in the taxi clearance. [RA-2018005]
- that the Air Traffic Services Provider ensures that its safety management system will identify and address safety hazards through the review of occurrences. [RA-2018-006]
- that the Civil Aviation Authority of Singapore requires the Air Traffic Services Provider to ensure that its safety management system will identify and address safety hazards through the review of occurrences. [RA-2018-007]
- that Scoot reviews its procedures to ensure that flight recorders are deactivated at the end of a flight following a significant occurrence. [RA-2018-008]
- that the Civil Aviation Authority of Singapore ensures that all Singapore Air Operator Certificate holders have procedures that ensure the deactivation of flight recorders upon completion of a flight following an accident or a serious incident. [RA-2018-009]
- that the Civil Aviation Authority of Singapore considers requiring commercial aircraft on Singapore’s register to install proximity sensors or cameras at the wing tips to assist pilots in making wing tip clearance decision. [RA-2018-010]
- that the Air Traffic Services Provider considers revising the piece of information in the Aerodrome Advisory Chart AD-2-WSSS-ADC-3, viz. “ACFT taxiing on TWY WA are not clear of ACFT pushback from ACFT stands C24, C25 & C26 until at the end of pushback”, to ensure that pilots will not miss the information. [RA-2018-011]
The Final Report was published on 19 March 2018.