What happened
On August 11, 2009, a UH-1H helicopter, registration NA-502, operated by the National Police Agency National Airborne Service Corps, crashed in a valley near the Beixi River in Sandimen Township, Pingtung County. The aircraft was engaged in a disaster relief mission following Typhoon Morakot, transporting supplies to the Ila community.
While flying eastbound through the Ailiao River valley, the aircraft's tail section struck an abandoned cable used for a cableway system. The impact caused the rear structure of the helicopter to separate from the main fuselage and snapped the cable. The aircraft lost control and plummeted into a slope on the south bank of the river. The crash resulted in 3 fatalities among the crew.
The investigation
The Taiwan Transportation Safety Board (TTSB) examined the wreckage and the surrounding environment. Investigators recovered broken segments of the cableway steel wire at the crash site. The investigation focused on the presence of the obstacle, the flight procedures used during mountain operations, and the crew's operational environment. The investigation also reviewed the operator's flight management manuals, training protocols, and the regulatory standards for marking aviation obstacles.
Findings
- The primary cause of the accident was the helicopter's tail section striking a steel cable used for a cableway system near the stabilizer.
- The abandoned cableway wires were unmanaged and lacked required aviation obstruction lights or markings, making them nearly impossible to detect during flight.
- The operator's flight management manuals lacked specific procedures for navigating unfamiliar mountain routes or inspecting ground obstacles.
- While the crew demonstrated situational awareness by performing reconnaissance during the initial approach, the high-pressure environment of the relief mission, combined with potential fatigue and the lack of detailed obstacle-avoidance procedures, contributed to the impact.
- There was a lack of updated, detailed information regarding man-made obstacles in mountainous terrain within the operator's aeronautical charts.