What happened
On November 16, 2013, a Cessna TU206G, registered JA4000, was conducting an aerial survey mission over Akita Prefecture, Japan. The flight, operated by Honda Airways Co., Ltd., was traveling from Saitama toward Noshiro City for photography work. During the flight, the pilot noticed that the oil pressure gauge had dropped below the normal 30 psi threshold.
As the flight progressed, the pilot attempted to maintain power by increasing the throttle, but engine performance began to decline. Shortly after, significant engine vibration and white smoke were observed. Realizing the engine was failing, the pilot initially diverted to Odate Noshiro Airport but eventually determined that a landing at the closed Akita Airport was necessary. As the aircraft approached the site, the engine ceased functioning entirely. The pilot executed a forced landing on a paved area within the closed airport. While the aircraft sustained minor damage and bounced during touchdown, there were no injuries to the pilot or the passenger.
The investigation
The Japan Transport Safety Board (JTSB) conducted an investigation involving an examination of the aircraft and an engine teardown. Investigators analyzed the flight path using GPS records and air traffic control communications. The investigation focused on the mechanical state of the engine, specifically looking for the source of the oil pressure drop and the subsequent engine failure. Physical inspections of the engine revealed fractures in the crankcase and the connecting rods of the fourth and fifth cylinders.
Findings
The investigation established that the engine failure was caused by a continuous loss of oil during flight. The primary cause was an oil leak resulting from the detachment of a hose connecting the housing extension to the oil gage rod housing on the engine body. This detachment was triggered by engine vibrations acting upon a loose connection.
Further analysis revealed that the hose clamp had been improperly installed; it was positioned toward the end of the hose and jutted toward the engine body, preventing the clamp from providing uniform or adequate pressure. This improper installation allowed the hose to eventually separate from the housing, leading to the depletion of oil and the subsequent catastrophic failure of the engine components.