Accident
On 27 May 2023, at approximately 11:45 local time, a Robin DR400/180 aircraft, registered F-BUSU, experienced a loss of engine power during the final approach to runway 08L at Tarbes-Laloubère aerodrome. The aircraft was operated by Aéroclub de Bigorre and was conducting a local flight with one pilot and one passenger on board. The forced landing on the adjacent golf course resulted in injuries to both occupants and the destruction of the aircraft.
Aircraft and Operator
The aircraft, a Robin DR400/180, was equipped with three fuel tanks: a left tank (40 litres), a right tank (40 litres), and a main rear tank (110 litres). The operator, Aéroclub de Bigorre, also operated several DR400/120 aircraft, which had a single tank and a simpler fuel selector. The accident aircraft featured a four-position fuel selector for tank selection, unlike the two-position switch on the single-tank variants.
Sequence of Events
According to statements and wreckage examination, the pilot conducted a local flight lasting approximately 35 minutes. On the return leg, he joined the downwind leg for runway 08L. On final approach, with the engine at idle, the pilot attempted to increase power but found no response. The propeller was rotating, but the engine was not delivering power. The pilot then prepared for a forced landing on the golf course, which featured numerous trees and a few clearings.
During the landing, the aircraft passed between two trees located six metres apart while skidding. The rear section of the fuselage struck one tree and ruptured, causing the aircraft to spin to the right before stopping. Examination of the propeller indicated the engine was not transmitting torque at impact.
Fuel System Examination
Post-accident inspection revealed that the left tank was empty, the right tank contained approximately 30 litres, and the main tank contained about 70 litres. The fuel system showed no anomalies, and the carburettor bowl and connecting hose contained only a small amount of fuel. The fuel selector valve was found in the "CLOSED" position, but the chief-pilot stated he moved it from "MAIN" to "CLOSED" to secure the wreckage. The electric pump switch was in the "OFF" position.
The pilot indicated that before the flight, he decided not to use the right tank to reserve fuel for the next pilot. He did not recall which tank he used for takeoff and did not think he operated the fuel selector during the flight. The passenger stated they started on the left tank and made no tank change during the flight.
Contributing Factors
Investigators determined that the left tank was used for the entire flight and landing circuit. The fuel in that tank was fully consumed, leading to fuel starvation and loss of engine power. Contributing factors included incomplete flight preparation regarding fuel distribution and a lack of training in fuel management for aircraft with multiple tanks.
Meteorological and Aerodrome Information
Weather conditions at the time were estimated as wind from 020° at 4 knots, CAVOK, temperature 24°C. The aerodrome had two parallel runways 825 m long; runway 08L for aeroplanes had a landing distance available of 630 m with a displaced threshold. The aerodrome chart noted that trees on the golf course required a steep approach slope.