What happened
On April 18, 2023, a Textron Aviation 172S, registration JA395A, operated by the Japan Coast Guard, was conducting a training flight for a commercial pilot certificate. The flight departed from Kitakyushu Airport with a trainee in the left seat and an instructor in the right seat. During a climb following stall training maneuvers over the Kunisaki Peninsula, the aircraft experienced a sudden drop in engine power.
At an altitude of approximately 3,400 feet, the crew heard a loud banging noise from the front of the aircraft. Simultaneously, the engine output displayed on the integrated instrument panel dropped from 100% to 60%, though no specific engine abnormality warnings were triggered. An aircraft flying nearby observed black smoke trailing from the exhaust of the JA395A.
As the aircraft continued to lose altitude despite attempts to adjust the power lever, the instructor determined that returning to Kitakyushu Airport was impossible. The instructor selected a suitable farmland site in Usa City, Oita Prefecture, specifically choosing a location free of overhead power lines. The instructor implemented emergency procedures, including activating the emergency locator transmitter and instructing the trainee to brace for impact. The aircraft performed a forced landing in the field, coming to rest upside down. While the aircraft was destroyed, there were no fatalities, and the two occupants sustained only minor injuries.
The investigation
The JTSB investigation examined flight data from the Garmin G1000 panel, engine data from the Full Authority Digital Engine Control (FADEC) unit, and video footage from onboard cameras. Investigators also reviewed maintenance records from the previous day, during which the engine's No. 1 fuel injector had been replaced. This work required the removal and reinstallation of the engine's intake hose.
Physical inspection of the engine revealed that the intake hose connecting the turbocharger to the intercooler had disconnected from the intercooler outlet. The investigation found that the lower hose clamp had detached and showed signs of corrosion, likely caused by battery acid leakage after the aircraft overturned. Furthermore, the investigation compared the detached clamp to an intact one, finding that the diameter of the detached clamp was significantly wider, suggesting insufficient tightening during the recent maintenance session.