What happened
On December 28, 2007, at approximately 08:45, a UH-1H helicopter, registration NA-520, operated by the National Police Agency Aerial Service, departed Songshan Airport for a search and rescue mission in the Zhongling mountain area of Wulai. The crew, consisting of a pilot, co-pilot, crew chief, and two special rescue members, was tasked with locating lost hikers.
At approximately 10:03, the aircraft located three individuals in need of assistance. During the process of hoisting the survivors into the aircraft, the hoist cable snapped. The sudden failure caused one rescue specialist and one of the individuals being rescued to fall to the ground, resulting in two injuries. Following the incident, the crew aborted the mission and returned to Songshan Airport by 10:34. The aircraft sustained no damage, and the remaining four crew members were uninjured.
The investigation
The investigation examined the flight path, the mechanical integrity of the rescue hoist system, and the operational procedures used during the mission. Investigators analyzed GPS data, which showed the aircraft was operating in an environment with irregular turbulent airflow. The investigation also reviewed the maintenance records of the hoist system and the training protocols for high-altitude mountain operations.
Technical testing of the rescue hoist (part number BL-20200-501) was conducted by Asia Airways. The testing confirmed that the hoist system was functioning normally and that there were no defects in the internal components or the mechanical load-bearing capabilities of the unit at the time of the accident.
Findings
- The aircraft was performing an Out-of-Ground-Effect (OGE) hover in turbulent air without clear visual reference points, which led to delayed corrections and an unstable hover.
- During the hoisting process, the aircraft shifted, causing the fleet angle to exceed the 35-degree limit.
- The cable snagged on a tree branch, creating a sudden tension spike that caused the cable to snap due to excessive instantaneous loading.
- There was a lack of standardized, integrated operating procedures between the Aerial Service and the Fire Department regarding risk identification and responsibility division during joint operations.
- The rescue specialist's training and the crew's resource management were insufficient for the complex environmental conditions encountered.