What happened
On October 23, 2008, a Bell 4लपुर 47 G 2 helicopter, registration F-BTSI, was engaged in a training flight near Sundhoffen. The flight, involving an instructor and a student pilot, had departed from Colmar aerodrome to practice approach, takeoff, and emergency procedures in a rural area. During the session, the instructor simulated a hydraulic failure without prior announcement, prompting the student to perform a side-slip landing in a clear field.
Following this maneuver, the student performed several takeoffs. During the final attempt, while the aircraft was at an altitude of approximately ten meters, the instructor took control of the aircraft with energetic inputs to reposition the helicopter into a hover within ground effect. This sudden movement caused the skids to strike the ground violently. The impact resulted in the main rotor blades striking the tail boom, causing the cabin to pitch forward and bringing the aircraft to a halt. The aircraft was destroyed.
The investigation
The investigation examined the wreckage and the flight sequence to determine the cause of the impact. Analysis of the accident site and the debris indicated that the helicopter was traveling at a high horizontal speed at the moment of impact.
Investigators also reviewed the training context. The student had recently resumed training after a thirteen-month hiatus caused by aircraft unavailability. The instructor noted that while the student was expected to make independent command decisions, the student often sought guidance on necessary actions. On the morning of the accident, the pair had completed a two-hour navigation flight. The instructor's specific technique for these maneuvers involved instructing the student to accelerate at a constant altitude within ground effect before initiating a climb, though a slight loss of altitude during acceleration was permitted.
Findings
- The primary cause of the accident was the inappropriate application of control inputs by the instructor during the attempt to transition the aircraft into a hover.
- The sudden and forceful movement of the controls led to the skids striking the terrain while the aircraft maintained significant forward momentum.