What happened
On May 11, 2004, at approximately 11:05 UTC, a Thrush Commander S-2R, registration CS-AJS, was performing agricultural sowing operations near Batal to distribute rice seeds. While flying at a low altitude of approximately 50 feet, fully loaded with wet rice seeds, the aircraft experienced a sudden engine failure.
The pilot attempted to manage the emergency by checking the fuel selector, engine controls, and magnetos, finding all in the correct positions. After initiating a left turn toward the only suitable landing area—an unflooded field—the pilot attempted to use the manual fuel pump and began an emergency discharge of the seed load. Although the engine briefly showed signs of restarting, the power could not be sustained. To avoid an irrigation ditch, the pilot performed a 180-degree turn to approach the field into the wind, but due to the low altitude and loss of power, the aircraft could only complete a 90-degree turn, forcing a landing across the width of the field.
Upon touchdown, the pilot chose to execute a ground loop to avoid overshooting the field into a flooded area. Due to the soft, uncompacted nature of the plowed soil, the right main landing gear collapsed, causing the right wing to strike the ground and the aircraft to slide approximately five meters. The pilot sustained minor injuries to the right arm.
The investigation
The GPIAAF examined the engine, propeller, and fuel systems. Post-accident testing showed that the engine could be restarted successfully and functioned normally for several minutes. The ignition system, magnetos, mixture control, and carburetor heat were all found to be operational. No mechanical failures were detected within the engine or its immediate accessories, and there was no evidence of contaminated fuel or blocked fuel lines.
However, a detailed inspection of the fuel tank ventilation system revealed a total obstruction in the air intake lines. The investigation noted that the position of the vent breather, located on the underside of the left wing, made it difficult to use protective covers. Furthermore, the aircraft's typical operating environment—unprepared airstrips with abundant dust, vegetation, and insects—increases the risk of such blockages.
Findings
- The primary cause of the engine failure was the obstruction of the fuel tank ventilation lines.
- The vent breather's location on the left wing underside prevented the effective use of protective covers.
- Operating from unpaved, dusty, or vegetated strips facilitates the clogging of air intakes by environmental debris or insects.
- The aircraft's landing gear collapsed because the right main wheel sank into the soft, plowed soil during the ground loop.