What happened
On July 10, 2011, a Cessna 208B, registered JA55DZ, operated by the Tokyo Skydiving Club, was conducting a skydiving flight near Honda Airport. The aircraft was carrying 20 people, including the pilot, a passenger, and 18 skydivers. During the final group of jumps, the pilot attempted to adjust the flight path and altitude at the request of a skydiver wearing a wingsuit.
As the aircraft was climbing at approximately 11,000 feet with the engine at full power, the pilot heard a small impact. Upon looking back, the pilot observed that the wingsuit diver had already exited the aircraft. The impact had caused significant dents and deformation to the leading edge of the left horizontal stabilizer. The skydiver sustained minor injuries to both legs, characterized by abrasions and bruises.
The investigation
The Japan Transport Safety Board (JTSB) examined the aircraft's flight history, the pilot's statements, and the skydiver's account. The investigation focused on the aircraft's configuration at the time of the exit, specifically noting that the aircraft was climbing at 100 knots, which was higher than the standard 70 to 80 knots used for diving. Investigators also analyzed the physical damage to the stabilizer, noting that the spacing of the dents closely matched the position of the diver's legs.
Findings
Investigators determined that the primary cause of the accident was the skydiver's failure to follow established exit procedures. Specifically, the diver did not request a "power cut" (reduction of engine power) before exiting, which is standard practice to ensure a safer separation from the airframe.
Several contributing factors were identified:
- The aircraft was flying at a higher-than-normal airspeed of 100 knots during the climb.
- The propeller slipstream at full power created strong, upward airflow around the left horizontal stabilizer.
- The high ram-air pressure acting on the wingsuit, combined with the diver's failure to maintain proper limb positioning during the initial exit, pushed the diver toward the airframe.
Safety action
The operating company has since revised its in-house skydiving manuals to better define procedures for changing flight conditions and has implemented regular coordination meetings between instructors and pilots to ensure standardized communication.