What happened
On 16 October 2015, a TigerAir Airbus A320, registration 9V-TRH, was performing a scheduled passenger flight departing from Singapore Changi Airport. During the take-off roll, the inboard and outboard fan cowls of the left engine detached from the aircraft. The cabin crew alerted the flight crew after a passenger noticed the engine interior was visible.
Upon reaching 8,000ft, the flight crew stabilized the aircraft and determined that engine parameters remained normal. However, during the subsequent approach to Changi, the crew activated the landing gear, which triggered a Master Warning indicating that the left main landing gear was not downlocked. Despite attempting a manual gravity extension, the warning persisted. The crew declared a Mayday and entered a holding pattern to reduce the aircraft's weight by burning fuel. After a low fly-past confirmed to ground engineers that the gear appeared secure, the aircraft landed safely with no injuries to the 178 people on board.
The investigation
Investigators examined the maintenance history of the aircraft, specifically a base layover completed the previous day. During this maintenance, a technician had opened the left engine fan cowls to check the oil level of the integrated drive generator. The investigation found that the technician did not follow the full manufacturer-prescribed procedures for closing the cowls and failed to record the activity in the aircraft logbook.
Furthermore, the investigation scrutinized the pre-flight walkaround inspections performed by the departure engineer and the flight crew. It was determined that these inspections relied on checking if the cowl surfaces appeared flush with the engine nacelle rather than physically verifying the latches. A simulation confirmed that unfastened latches can still appear flush and can be obscured by the engine's structure or the angle of view from a standing position.
Findings
- At least three of the four latches on the left engine were unfastened prior to departure.
- The loss of the cowls was caused by airflow forces acting on the unlatched components during high-speed take-off.
- The landing gear warning was an erroneous indication caused by debris from the fan cowl striking a proximity sensor on the left main landing gear door.
- Maintenance and flight crew inspections were inadequate because personnel did not crouch or squat to visually confirm the latches were secured, relying instead on an unreliable assessment of surface flushness.
- The airport's FOD detection system failed to immediately identify the debris on the runway due to insufficient camera resolution.