What happened
On March 12, 2000, at 10:20 UTC, a privately owned Jurca MJ55, registration F-PJJR, crashed at Valence airport in France during an aerobatic flight session. The aircraft, an amateur-built model with approximately 58 total flight hours, was performing maneuvers over the airfield with one pilot and one passenger on board.
Witnesses reported that the pilot announced the start of aerobatic maneuvers before the aircraft was seen at the top of a loop or roll. During the maneuver, debris was observed falling from the aircraft like rain. The aircraft then entered a descending roll and struck the ground within the airfield perimeter. One witness observed the pilot attempt to bail out at an altitude of approximately 100 meters, but the parachute failed to deploy.
The investigation
The investigation focused on the wreckage and the construction methods of the aircraft. Investigators found that the wing spar was broken in several places and the flight controls were deformed and broken. Notably, pieces of the left wing's leading edge and skin were found scattered two kilometers from the main impact site, indicating a structural failure in flight.
Examination of the wing structure revealed significant deviations from the original designer's plans. The builder had modified the wing by using a single continuous piece of plywood for the skin rather than two separate panels, and had reduced the number of longitudinal spacer blocks (cales) to a single row located only in the center of the spar, rather than the two rows specified in the design. Furthermore, investigators discovered that the spacer blocks on the upper (extrados) side of the spar had not been glued to the spar.
Findings
- The primary cause of the accident was the loss of the left wing skin in flight.
- This failure was directly caused by the failure to glue the spacer blocks to the upper surface of the wing spar.
- The builder's decision to modify the original design—specifically simplifying the construction by using fewer spacer blocks and a single-piece skin—increased the structural complexity and difficulty of the gluing process.
- The lack of glue on the upper side of the spar meant the skin was not properly secured against the aerodynamic suction (negative pressure) experienced on the upper wing surface during flight.
- The builder, working alone and without professional aeronautical construction experience, likely omitted the glue application due to the time pressure and difficulty of closing the wing structure.
- The regulatory inspections performed during the construction process were unable to detect these internal structural defects, as the errors were hidden within the closed wing structure.