Serious incident Boeing 737-8SA (WL) 9V-MGM,
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ASN Wikibase Occurrence # 195398
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Date:Sunday 6 December 2015
Type:Silhouette image of generic B738 model; specific model in this crash may look slightly different    
Boeing 737-8SA (WL)
Registration: 9V-MGM
MSN: 44229/5572
Year of manufacture:2015
Fatalities:Fatalities: 0 / Occupants: 153
Aircraft damage: Minor
Category:Serious incident
Location:Singapore-Changi International Airport (SIN/WSSS) -   Singapore
Phase: Pushback / towing
Nature:Passenger - Scheduled
Departure airport:Singapore-Changi International Airport (SIN/WSSS)
Destination airport:Phuket International Airport (HKT/VTSP)
Investigating agency: TSIB Singapore
Confidence Rating: Accident investigation report completed and information captured
The Boeing 737-800 parked at Bay F41 in Singapore Changi Airport was ready for departure. A ground operation crew pushed back the aircraft from the bay using an airtug and a towbar. The aircraft was to be positioned on Taxiway C2 facing south-east. It began raining during the pushback.
The aircraft’s right engine was started as the aircraft was being pushed back from Bay F41. After completion of the pushback, the aircraft was pulled forward to an End-of-Tow line that was marked on the ground. During the forward pull, the aircraft’s left engine was started. Following that the airtug driver experienced difficulty in controlling the moving aircraft. He sensed that the aircraft was pushing the airtug and causing the airtug to accelerate. The airtug also tended to drift to the left. The airtug driver tried to slow down the aircraft by applying brakes gradually, but the airtug continued to drift to the left. He then applied full brakes to stop the aircraft before reaching the End-of-Tow line. As a consequence, the towbar broke.
The airtug swung to the left, 180° anti-clockwise, and hit the left side of the aircraft which had surged forward after the towbar had broken off, resulting in damage to the lower left side of the aircraft fuselage just behind the radome. There were no injuries to any person.

The investigation team believed that the sequence of the airtug’s swinging around was likely to be as follows:
- The airtug was left of the aircraft at some stage during its manoeuvre to bring the aircraft in line with the taxiway centerline during the pull forward.
- However, when the centres of gravity of the airtug, towbar and aircraft were not in line, the forward momentum of the aircraft created a turning moment and forced the airtug, through the towbar, to turn further to the left.
- The angle between the centerline of the airtug and the centerline of the towbar increased. When the angle reached 60°, the lunette mount flat came into contact with the stop plate in the tow hitch. Further turning, however, caused the lunette mount flat to press on the stop plate and dent it. By the time the lunette mount flat became stuck in the tow hitch, the angle had reached about 96°.
- After this, the airtug and towbar were, together, pushed further to the left by the momentum of the aircraft.
- The “folding over” (or “jack knife” effect) of the airtug against the end of the tow bar caused the skin on the left side of the towbar tube just after the lunette mount flat to tear, thus sending the airtug swinging further anti-clockwise.
- The complete disconnection of the towbar from the airtug also caused the aircraft to surge forward and collide with the airtug which was swinging back towards it.

The investigation team believed that the sensation of being pushed by the aircraft could be related to the brake applications. That the aircraft was being towed by the airtug at a relatively high speed, i.e. 11 km/h or more, could make the sensation more pronounced.
The investigation team also believed that it is unlikely that the second engine could have contributed to the airtug driver’s sensation of the airtug being pushed by the aircraft as, at the time of the incident, the second engine’s power was still well below idle thrust.

Accident investigation:
Investigating agency: TSIB Singapore
Report number: 
Status: Investigation completed
Download report: Final report


Revision history:

15-May-2017 18:00 harro Added
15-May-2017 18:06 harro Updated [Narrative]
15-May-2017 18:13 harro Updated [Source]

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