What happened
On January 14, 2007, at 16:20, a Grob G 109 B motor glider, registered F-CAQN, was conducting a local instructional flight at Maubeuge aerodrome. The flight was operated by a club and carried an instructor and a student pilot. During the approach to runway 23, the instructor, seated in the right-hand seat, had planned to take control of the aircraft at the beginning of the final approach.
The approach was stabilized with the engine at idle, the propeller at full fine pitch, and a speed between 110 and 115 km/h, with the airbrakes partially extended. As the aircraft reached the flare at approximately two to three meters above the ground, it suddenly pitched nose-down. The instructor was unable to prevent the aircraft from striking the runway hard. The propeller made contact with the ground, causing the aircraft to veer left off the runway and undergo a ground loop. The aircraft sustained damage during the event.
The investigation
Investigators examined the aircraft and found no mechanical anomalies that could have caused the loss of control. The flight manual specifies that the stall speed for the Grob G 109 B at a maximum weight of 850 kg is 83 km/h in stabilized horizontal flight with reduced power and fully extended airbrakes. While the airbrakes are highly effective at reducing glide ratio, the manual does not specify a nose-down pitching effect. Additionally, the aircraft was not equipped with a stall warning system.
The investigation focused on the instructor's experience and cockpit configuration. The instructor typically conducts instruction in a Scheibe SF 28 tandem aircraft. Because that aircraft was unavailable, the instructor used the Grob G 109 B in a side-by-side configuration. Although the instructor held a TMG qualification, his previous experience in the right-hand seat of this specific model was limited to observing other pilots without actively flying the controls. The instructor noted that being right-handed, he was unaccustomed to operating the control stick with his left hand while managing the airbrakes with his right hand. He also indicated that he may have pushed the stick forward while attempting to retract the airbrakes to delay the landing.