What happened
On June 8, 2003, at 14:15, a Jodel DH 251 amateur-built aircraft, registration F-PCGO, was conducting a private flight from Montélimar to Annecy. While flying near the Chatuzange-le-Goubet ultralight airfield at an altitude of approximately 2,000 feet, witnesses on the ground reported hearing a sound similar to helicopter blades. Shortly after, observers noted structural components and a white plate detaching from the aircraft.
The aircraft entered a steep right bank with a nose-down attitude before momentarily leveling out. It then entered a descending roll. During this sequence, additional pieces of the aircraft broke away. The aircraft subsequently struck a seven-meter-high power line and crashed into the ground, resulting in a post-impact fire that destroyed the wreckage. The pilot was killed in the accident.
The investigation
Investigators examined the wreckage and recovered several key components. The right aileron and right flap were found 100 and 120 meters upstream of the impact site, respectively, while the left aileron was located 150 meters east of the crash site. The distribution of these parts confirmed that the control surfaces separated from the aircraft during flight.
Analysis of the left aileron revealed a broken metal bellcrank, with the fracture surface showing two distinct modes of failure. The control cables were found frayed, indicating they had been subjected to extreme tension. Furthermore, while the aileron hinges were secured with screws and nuts, the holes in the hinge bases had become enlarged and oval-shaped. The investigators also found that the captive nut fasteners on the spar were not fully secured.
Findings
In 1999, the pilot had constructed a new wing based on DR 250 plans, which included a reinforced main spar and modifications to accommodate an extra passenger. While new cables and pulleys were installed, the pilot reused the ailerons, flaps, and hinges from the previous wing. Additionally, in April 2003, the pilot installed a new propeller to improve aircraft performance.
The investigation concluded that the ovalization of the hinge bases and excessive play in the fittings allowed the ailerons to move freely around their axis. This instability triggered aeroelastic flutter. The installation of the new propeller increased the aircraft's operating speed, which significantly raised the probability of this flutter phenomenon occurring, ultimately leading to the separation of the control surfaces.