What happened
On June 16, 2023, at approximately 11:32 JST, a privately owned Cessna T303, registration JA5309, was undergoing an engine function check on the apron at Naha Airport. The pilot was preparing for a flight to Yao Airport via Amami Airport. During the power increase on the No. 1 (left) engine, the pilot observed white smoke and a burning smell emanating from the engine area. Simultaneously, the "L ENG FIRE" warning light illuminated.
In response, the pilot immediately shut down both engines. Upon exiting the aircraft with a portable fire extinguisher, the pilot noted that the white smoke was increasing. Although the pilot attempted to suppress the flames using the onboard extinguisher, the fire continued to burn until airport fire services arrived approximately seven minutes later to extinguish the blaze with water. There were no injuries to the pilot.
The investigation
The Japan Transport Safety Board (JTSB) examined the damage to the aircraft's left engine cowling and internal components. The investigation revealed that the turbine part of the exhaust turbocharger had detached from the exhaust tailpipe. Additionally, the wastegate valve connection had also separated. The inspection found that the heat shield, vacuum system hoses, and portions of the engine cowling had been scorched or burnt.
Investigators focused on the coupling used to join the turbine and tailpipe. This component showed widespread corrosion, fractures in the outer band, and cracking in the v-retainer segment near the spot welds. Furthermore, the investigation identified that the coupling was a non-specified part, as the part number marked on it did not match the manufacturer's approved parts list, and it lacked the required maximum tightening torque markings.
Maintenance records indicated that the aircraft had not undergone a required periodic inspection since November 2022, as more than seven months had passed, exceeding the six-month interval required by the maintenance manual. The pilot was also unaware of the specific six-month inspection requirement.
Findings
- The fire was triggered by the failure of the exhaust turbocharger coupling, which allowed hot exhaust gases to escape and ignite the heat shield, hoses, and cowling.
- The use of a non-specified part for the coupling likely contributed to the structural failure of the component.
- The pilot had noted unusual signs during previous inspections—including melted plastic-like debris and black discoloration on the cowling access door—but did not perform a more detailed inspection.
- The coupling was positioned in a location that was not visible even when the engine cowling access door was opened, making detection difficult during standard pre-flight checks.