What happened
On 15 August 2019, a Bachoffer BA-01, registration F-PCBJ, was performing a local flight from the Pamiers-Les Pujols aerodrome. Shortly after departing from runway 27, witnesses observed the aircraft level off at a low altitude before pitching into a steep nose-up attitude. The aircraft subsequently experienced a left-wing stall and collided with the ground. The pilot, who was the designer and builder of the aircraft, sustained one fatality.
The investigation
The investigation focused on the aircraft's structural modifications and weight and balance configuration. The Bachoffer BA- 01 was a unique, amateur-built wooden aircraft based on the design of the Bilouis. The builder had significantly modified the original design by extending the fuselage and increasing the wingspan and wing area.
Investigators examined the wreckage and found the engine and propeller were in good condition, with the propeller blades showing damage consistent with rotation under power at impact. While the elevator trim control linkage was found disconnected, the investigation determined this separation likely occurred due to the forces of the ground impact rather than being the cause of the accident.
Furthermore, the investigation compared the aircraft's weighing records with its three-view drawings. Discrepancies were found in the center of gravity (CG) reference datum, revealing that the actual CG was significantly further aft than documented. The estimated CG during the flight was approximately 50% of the Mean Aerodynamic Chord (MAC), far exceeding the maximum allowable limit of 36%.
Findings
- The aircraft's aft center of gravity created a natural nose-up tendency and longitudinal instability.
- To compensate for this imbalance, the pilot had adjusted the trimmable horizontal stabilizer to a high positive angle (+7.2 to +7.8°), which created a nose-down aerodynamic moment.
- This specific configuration increased the risk of a premature stall of the horizontal tail and made the aircraft difficult to control, particularly at low speeds.
- The pilot's lack of recent experience in this specific, difficult-to-handle aircraft may have contributed to the loss of control during the takeoff phase.