What happened
On December 14, 2004, an EADS SOCATA TB 20, registration F-GGNZ, was conducting a training flight departing from Moulins aerodrome. The aircraft was occupied by an instructor and three students. During the initial climb, while passing through 4,000 feet, the instructor noted a sudden loss of engine power. Following standard emergency procedures for an in-flight engine failure, the instructor activated the electric fuel pump, after which engine parameters appeared to return to normal.
The crew decided to return to Moulins. However, after three minutes of cruise flight, the instructor deactivated the electric fuel pump, at which point engine power rapidly declined. Despite repeated attempts to restart the engine and following emergency protocols, the engine failed to recover. The instructor declared an emergency on the Saint-Yan approach frequency, provided a position relative to the Mouless VOR, and announced an intention to land in a field. The aircraft subsequently performed an emergency landing in a harvested cornfield at L’Augère, near Dompierre-sur-Besbre.
The investigation
Post-landing inspections of the aircraft's ignition, intake, and fuel systems revealed no immediate anomalies. Investigators found that while the electric pump functioned normally when operated independently, fuel flow ceased whenever it was placed in series with the mechanical pump.
Upon disassembly of the mechanical pump, which utilizes a flexible diaphragm, investigators discovered that a washer intended to secure the pushrod was loose. This washer had shifted into a position that obstructed the pump's check valve, thereby interrupting fuel delivery to the injection unit.
Findings
- The engine failure was caused by a manufacturing defect in the mechanical fuel pump, specifically a failure to properly crimp the pushrod retaining washer.
- This defect caused the washer to obstruct the check valve, cutting off the fuel supply.
- While the manufacturer and the FAA had previously issued corrective actions for similar pumps, the specific unit installed in F-GGNZ was not part of the previously identified defective batches.
- Subsequent inspections by the operator, SEFA, identified three other pumps in their fleet with similar non-compliant pushrod diameters and defective crimping.