What happened
On February 10, 2000, a De Havilland Canada DHC-6 Twin Otter, registration F-GUTH, was performing a training flight during a positioning maneuver from Courchevel to Lyon. During the takeoff roll on runway 05, the aircraft reached approximately 60 knots as it transitioned from the flat section of the runway to the downward slope. At this moment, the aircraft experienced a sudden leftward veer. The nose gear assembly failed, causing the aircraft to veer off the runway and strike a snowbank. The impact caused the aircraft to lift slightly, strike the left main gear against the snow, and ultimately flip onto its back. Both pilots on board were uninjured.
The investigation
The investigation focused on the structural integrity of the landing gear and the operational conditions at the Courchevel altiport. Investigators examined the wreckage, noting that the nose wheel had detached from the fuselage along with part of the steering fork. The left wing had been torn from the aircraft, and the left horizontal stabilizer and elevator were damaged.
Technical inspections of the engines, propellers, fuel, and lubrication systems revealed no anomalies. Maintenance records for the F-GUTH were also found to be in order. While a minor oil leak was discovered in the nose gear steering actuator due to unfastened bolts, this was not considered a contributing factor to the structural failure. Because the aircraft was not equipped with flight recorders, investigators relied on wreckage analysis and crew testimony to reconstruct the sequence of events.
Findings
- The investigation established that the nose gear fork suffered a static failure due to an overload.
- The failure occurred at the point where the runway slope changes abruptly.
- It is highly probable that an insufficient forward pressure on the control column, or a momentary release of pressure, allowed the nose to lift prematurely. When the nose gear subsequently struck the ground at high speed (60 knots), the resulting impact force exceeded the structural limits of the fork.
- The loss of directional control led to the aircraft exiting the runway and the subsequent rollover.