History of the Flight
On 30 October 2020, a Cessna 401B (registration N517HC) departed from Toussus-le-Noble aerodrome at 17:10 for a local flight of approximately 30 minutes. The pilot-in-command occupied the left front seat, a passenger who was also a pilot sat in the right front seat, and a mechanic sat in the rear. This was the first flight after the aircraft had been in storage for over twelve years, followed by approximately eight months of work to return it to airworthy condition. The purpose of the flight was to check overall correct operation.
Shortly after takeoff, the temperature of cylinder No. 4 on the left engine exceeded 460°F (around 238°C), displayed in red on the engine computer screen and activating an alert light. The mechanic-passenger suggested it might be a false alert due to a faulty temperature probe. The pilot and front-seat passenger reduced power and stabilized the aircraft at 1,500 ft. The temperature decreased and the light went out. Based on the mechanic's opinion, the pilot-in-command decided to continue the flight.
At approximately 17:20, on the return leg, the alert light reappeared, and the three occupants observed a fire in the left engine. The pilot, assisted by the front-seat passenger, cut off the fuel supply to the left engine, which did not noticeably affect the fire, and then attempted to feather the propeller. The front-seat passenger declared a MAYDAY on the Toussus-le-Noble tower frequency. The pilot-in-command initially decided to head for runway 25 but, uncertain of reaching the runway, elected to perform an emergency landing in a ploughed field. The landing was carried out with the landing gear retracted and flaps fully extended. The aircraft came to a stop, and the occupants evacuated without difficulty. Firefighters, alerted by the controller, arrived and extinguished the fire, which remained confined to the left engine.
Aircraft Information
N517HC is a Cessna 401B, a twin-engine aeroplane equipped with two 300-hp Continental TSIO-520-E piston engines. The aircraft had been owned by the maintenance workshop until February 2020 and had not been in service since 2006, stored in a workshop hangar without specific preservation measures. The left engine was manufactured in 2000 and installed that same year; its total operating time was 408 hours as of 2020. The engine manufacturer recommended a maximum time between overhauls of twelve years, including storage periods, which had been exceeded by approximately eight years.
The work to return the aircraft to airworthy condition was performed under the supervision of a French Inspection Authorization (IA) inspector. A pre-sale borescope inspection of the cylinders was reported as satisfactory, though no photographs were provided to the BEA. The 100-hour inspection was completed, and an Approval for Return to Service was signed by the IA inspector.
Personnel and Weather
The 47-year-old pilot-in-command held a Commercial Pilot Licence with Instrument Rating Multi-Engine, obtained in 2018, and had about 650 total flight hours, including 183 hours on twin-engine aircraft. The front-seat passenger, aged 51, held an Airline Transport Pilot Licence and had 4,450 hours total. The mechanic-passenger, head of the workshop that returned the aircraft to airworthiness, held a Part-65 FAA mechanics licence. The owner of the aircraft held a Private Pilot Licence with instrument and multi-engine ratings but no experience on this model.
The automated METAR at 17:30 reported wind from 220° at 8 kt, visibility greater than 10 km, few clouds at 1,700 ft, overcast at 3,400 ft, temperature 14°C, dew point 11°C, and QNH 1024. The weather was suitable for VFR flight with clear sky and no turbulence.
Consequences and Damage
The aeroplane was substantially damaged. The fire was confined to the left engine and was extinguished by the responding firefighters. No injuries were reported.
Probable Cause
Not specified in the report.