What happened
On 11 October 2023, a Thrush S2R-T660, registration EC-OCK, was performing a positioning flight from Córdoba Airport to Seville Airport. The flight was part of a logistical movement to prepare the aircraft for a future ferry flight to Chile. While descending through 1,500 feet near the municipality of Lora del Río, the pilot experienced a loss of engine power followed by a complete engine shutdown.
Upon realizing the engine had failed, the pilot executed emergency procedures, including activating the electric fuel pump and auto-ignition, but the engine failed to restart. The pilot then prepared for an emergency landing, feathering the propeller and selecting a landing site within an orange grove. The aircraft struck the ground with significant energy, causing substantial damage to the airframe, engine protection panels, and the hopper structure. The pilot was able to exit the aircraft without assistance and sustained no injuries.
The investigation
The CIAIAC investigation focused on the fuel system and the configuration of the aircraft's "ferry kit," which had been installed to convert the firefighting hopper into an additional fuel tank for long-range flight. Investigators examined the aircraft's maintenance records, the fuel system components, and the physical evidence at the crash site.
Technical analysis revealed that the engine shutdown was caused by an interruption in the fuel supply due to air entering the fuel circuit. The investigation noted that the modified firefighting gates positioned the hopper's fuel intake at the rear and higher than specified in the engineering bulletin. During the descent, the movement of fuel within the hopper caused the intake to draw in air instead of fuel.
Findings
- The primary cause of the accident was an emergency landing in an unprepared area following an engine shutdown caused by a fuel supply interruption.
- The interruption in fuel supply was triggered by air entering the circuit, which led to a loss of power and eventual engine flame-out.
- The ferry kit's fuel selector lever lacked a position lock or guard, allowing it to be moved into an intermediate position between the wing and hopper settings.
- This intermediate position allowed for simultaneous fuel supply from both the wing and hopper tanks, which contributed to the instability of the fuel flow.
- Vulnerabilities in the ferry kit were identified, including the lack of a fuel quantity gauge for the hopper tank and the potential for installation errors or damage during the frequent installation and removal of the kit.
Safety action
- The manufacturer, Thrush Aircraft LLC, has been issued a safety recommendation to modify the ferry fuel system kit. The recommendation specifies that the fuel tank selector should include a shut-off valve that locks in the selected position to prevent accidental movement to intermediate positions.