What happened
On August 1, 2010, a privately owned Robinson R22 Beta, registered JA22NE, was conducting a familiarization flight from Iki Airport toward the Kamou Helipad in Kumamoto Prefecture. The flight, which included the captain and one passenger, proceeded normally until the final approach phase.
As the aircraft approached the destination, it maintained a ground speed significantly higher than typical approach speeds—approximately twice the normal rate. During the descent, the aircraft drifted toward utility lines running along a nearby road. In an attempt to avoid these obstacles, the pilot's actions led to a rapid loss of rotor stability. The aircraft entered a steep descent, banking to the right, and struck a paddy field approximately 160 meters north of the helipad. The impact destroyed the aircraft, and both occupants were killed.
The investigation
The Japan Transport Safety Board (JTSB) examined the wreckage, GPS data, and witness accounts to reconstruct the flight path. Investigators analyzed the engine and rotor components, noting that the main rotor RPM had decayed significantly prior to impact. Witnesses at the scene reported seeing the aircraft bank sharply and observed a noticeable decrease in the speed of the main rotor blades before the crash.
Technical analysis of the aircraft's flight profile revealed that the aircraft was approaching from an unapproved direction and was flying at an excessive airspeed for the final stage of the landing. The investigation also considered meteorological data, which indicated the presence of fitful gusts from the southwest during the time of the accident.
Findings
- The primary cause of the accident was a catastrophic main rotor stall, which resulted in a near-total loss of lift and rendered the aircraft uncontrollable.
- The stall was likely triggered when the pilot pulled up on the collective pitch to avoid utility lines while the main rotor RPM was already in a decayed state.
- The aircraft was operating at a high rate of descent and an excessive airspeed, roughly double the standard approach speed, during the final approach.
- A heavy left rudder input, intended to correct a right yaw caused by crosswinds, likely increased the engine load and contributed to the initial decay of the rotor RPM.
- The aircraft's approach path deviated from the approved landing area.