What happened
On the night of December 1, 2008, a Japan Coast Guard Bell 412 helicopter, registered JA6713, was conducting a scheduled patrol and photography training mission near Miyakojima, Okinawa. The flight originated from Ishigably Airport, with the crew intending to practice low-altitude hovering and imaging near a patrol boat and an uninhabited island.
During the mission, the crew attempted to approach a Coast Guard patrol boat for training. After an initial aborted approach due to the boat changing course, the pilot attempted a second approach. While maneuvering at approximately 200 feet, the pilot attempted to manually decelerate the aircraft to transition into a hover. During this maneuver, the aircraft's nose pitched up excessively, leading to a rapid loss of airspeed and altitude. The main rotor blades struck the sea surface, causing the aircraft to ditch in the waters east-northeast of the Ikema Island lighthouse. Despite the impact and the destruction of the aircraft, all five crew members successfully evacuated via a lifeboat and were rescued by the patrol boat.
The investigation
The Japan Transport Safety Board (JTSB) examined the wreckage and interviewed the crew, including the captain, copilot, and mechanic. The investigation focused on the flight controls, the autopilot settings, and the visibility conditions at the time of the accident. Investigators analyzed the aircraft's instrumentation, specifically the radio altimeter and autopilot switches, and reviewed the flight logs and maintenance records. The investigation also considered the impact of the searchlight used during the mission on the crew's spatial perception.
Findings
- The primary cause of the accident was the unintended excessive nose-up attitude during deceleration, which led to a rapid descent and subsequent impact of the rotor blades with the water.
- The pilot failed to recognize the descent in a timely manner due to difficult night-time visibility and the halation effect caused by the patrol boat's searchlight, which obscured the horizon.
- There was insufficient coordination between the pilot and copilot regarding altitude verification.
- The pilot may have inadvertently activated a standby button on the cyclic stick, which deactivated the radio altimeter (RADALT) function, further complicating altitude awareness.
- The pilot's decision to continue the training despite time constraints contributed to a rushed approach with insufficient downwind distance.