Incident Overview
On July 14, 2023, at approximately 15:06 Japan Standard Time, a Cessna 172R (registration JA10AZ) operated by Okayama Air Service Co., Ltd. experienced a continuous engine stoppage in flight near Kohnan Airfield in Okayama City, Okayama Prefecture. The aircraft was conducting a training flight for a commercial pilot certificate, with a trainee in the left pilot seat, a captain as instructor in the right seat, and a passenger in the right rear seat. The three occupants were not injured, and the aircraft was not damaged.
Flight History
The flight departed Kohnan Airfield at 13:07 for touch-and-go training at Hiroshima Airport, then returned to Kohnan Airfield. After three touch-and-go landings on Runway 09 using the south side traffic pattern, the aircraft entered the north side traffic pattern for a full-stop landing. While on the base leg at about 800 ft, the trainee set engine revolutions to 1,500 rpm but later noticed a drop to approximately 1,000 rpm. The trainee increased the rpm to about 2,000, then adjusted back to 1,500. When lowering flaps from 10° to 20°, the revolutions again fell below 1,000 rpm, and the trainee felt no thrust, as if the propeller were windmilling. At about 15:06, the captain judged the engine had stopped and took over control. Two restart attempts were unsuccessful. The captain raised flaps to 0° and continued the approach at about 65 kts, gliding to a landing on Runway 09. The propeller stopped rotating during the landing roll. At 15:08, the aircraft vacated the runway via Taxiway T4 and stopped on the taxiway.
Post-Incident Examination
Examination of the airframe and engine after the incident revealed no failures. A ground engine operation test found no abnormalities. The aircraft's weight and center of gravity were within allowable ranges at the time of the incident.
Emergency Procedures and Fuel System Notes
The aircraft's Pilot's Operating Handbook includes engine restart procedures for in-flight failure, such as setting the fuel selector valve to BOTH, turning on the auxiliary fuel pump, and ensuring the mixture is rich. The fuel system includes a reservoir tank with about 1.7 liters of fuel, sufficient for about 10 to 15 minutes of engine operation at 1,500 rpm if fuel from the main tanks is interrupted. The engine design and manufacturer note that air mixed in the fuel line or fuel injection servo can prevent proper fuel delivery and may cause engine shutdown. Additionally, excessive fuel vapor, which can occur during extended low-rpm operations or in warm conditions, may lead to vapor lock and engine stoppage. The investigation did not determine a specific cause for the engine stoppage.