What happened
On May 6, 2004, an EADS SOCATA TB 20 was conducting a qualification extension flight at La Baule aerodrome. Following several takeoffs and landings, the instructor directed the pilot to begin a training exercise. During the approach for runway 29, the crew heard the "gear not down" audible warning. The instructor alerted the pilot to the fact that the landing gear had not been extended, prompting the pilot to operate the gear lever.
As the aircraft approached the runway, the pilot fully extended the flaps to correct a high trajectory. During the landing roll, the main gear made contact with the runway first, followed by the nose gear. However, the nose gear subsequently began to retract progressively. This caused the propeller to strike the ground, resulting in a bent propeller and damage to the engine cowling. There were no injuries to the two occupants on board.
The investigation
Investigators examined the aircraft's landing gear systems and electrical components. The inspection confirmed that the landing gear position indicator lights were functional and that the red warning light (indicating gear in motion) extinguished once the main gear was locked. However, the green indicator for the nose gear remained unlit, and the nose gear failed to lock in the down position.
Technical analysis revealed that the nose gear extension mechanism stopped prematurely. The investigation focused on the electrical wiring of the nose gear limit switch. It was discovered that during a previous maintenance procedure, the wiring for the micro-switch had been soldered. This repair had made a flexible assembly rigid, preventing it from adapting to the natural movements of the landing gear strut.
Findings
- An inappropriate maintenance operation involving the soldering of wiring at a limit switch created a rigid point in a component that required flexibility.
- A broken wire near the solder point prevented the electrical contact necessary to signal the completion of the gear extension.
- The failure of the nose gear to lock prevented the hydraulic sequence from completing, leading to the gear's retraction under load.
- The crew failed to detect the mechanical anomaly during their final landing checks.