What happened
In the early hours of 29 November 2017, a Boeing 777-200, registration 9V-SQK, was being moved between maintenance bays at Singapore Changi Airport. While the aircraft was being towed along Taxiway South Cross 1, a diesel-powered Kalmar Towbarless 190 tow tug suddenly caught fire.
The towing crew, which included a driver, a headset man, and a certifying technician positioned in the aircraft cockpit, noticed vibrations followed by engine failure and visible flames emerging from the area behind the tug's cabin. The driver attempted to suppress the flames using an onboard 2 kg dry powder extinguisher, but the fire continued to spread. The technician in the cockpit activated the aircraft's parking brakes and alerted ground control before evacuating the aircraft via a slide raft.
Airport rescue and firefighting services responded to the scene. While a domestic tender arrived first to manage the spread, the fire was eventually extinguished by foam tenders. There were no injuries reported, though the tow tug was destroyed and the 9V-SQK sustained heat damage to its radome, nose landing gear, tires, and various electrical and hydraulic components within the nose gear wheel well and fuselage skin panels.
The investigation
Investigators examined the mechanical state of the tow tug's transmission system and the maintenance protocols of the service provider. The inquiry focused on the failure of the transmission shaft assembly and the effectiveness of the emergency response and fire reporting chain between Apron Control, Air Traffic Control, and the firefighting services.
Findings
- The investigation identified that the bolts securing the output flange retainer plate on the transmission shaft assembly had loosened.
- The tow tug manufacturer's manual lacked sufficient detail regarding the maintenance of the transmission shaft assembly and its connections.
- The maintenance program used by the service provider was insufficient because it relied on the manufacturer's incomplete instructions.
- There were identified gaps in the communication chain, specifically regarding how quickly and accurately fire information was relayed to the airport rescue and firefighting service.
Safety action
Following the incident, the maintenance provider implemented more rigorous inspection schedules, including a seven-day mandatory check of transmission shaft assemblies and enhanced lubrication procedures. The aerodrome operator also increased the required capacity of fire extinguishers on airside vehicles and updated fire reporting protocols to ensure the firefighting service is notified more directly and promptly.