Accident to the Bachoffer BA-01 registered F-PCBJ on 15/08/2019 at Pamiers Les Pujols (Ariège)

Cat. 2 investigation report: simplified-format report, adapted to the circumstances of the occurrence and the investigation stakes.

The pilot designed and built his aeroplane single-handedly based on the drawings of another amateur-built aeroplane, the Bilouis, an aeroplane with two seats in tandem configuration. He deviated significantly from the original drawings by extending the fuselage, increasing the wingspan and the wing area without discussing the consequences of this with the designer of the Bilouis.
During the first test flight, the pilot observed a problem of stability on the pitch axis. It seems that this problem was subsequently corrected and deemed acceptable to the pilot after the sixth test flight. However, the pilot mentioned that he still experienced difficulties manoeuvring the aeroplane longitudinally.
The investigation showed that the aeroplane’s actual centre of gravity was significantly further aft than specified in the aeroplane’s documentation and the weighing record in particular. This very aft centre of gravity caused a steep nose-up moment. It is very likely that the pilot used the on-ground adjustment system to set the angle of the trimmable stabilizer to offset this nose-up moment. This adjustment balanced the aeroplane in a normal flight situation but could not correct the instability resulting from the aeroplane’s aft centre of gravity. Moreover, this aft centre of gravity and this adjustment of the horizontal stabilizer induced a risk of deteriorating the performance of the aeroplane in the event of a stall. The statements suggested that the pilot had been aware of his aeroplane’s balance and stability problems. However, it is likely that he had not been aware that it was not possible to solve these problems by the adjustment of the horizontal stabilizer alone.
On the day of the accident, after a long period of not using the aeroplane, the pilot lost control of the aeroplane at take-off. The aeroplane collided with the ground after adopting a steep nose-up attitude. The pilot’s lack of recent experience in this aeroplane that was particularly difficult to control, may have contributed to the loss of control in flight during take-off.