What happened
On October 16, 2013, an MBB/Kawasaki BK117B-2 helicopter, registration B-77009, operated by Chung Hsing Airlines, crashed while performing a supply mission at the Yushan North Peak helipad. The aircraft was tasked with transporting personnel and supplies to the Yushan weather station.
After completing an initial supply run from the Tataka landing site, the aircraft commenced a second trip to the North Peak helipad carrying the crew and several boxes of supplies. At approximately 08:08, as the helicopter was hovering only 3 to 4 feet above the ground during its landing approach, the nose suddenly drifted to the right. The aircraft began a clockwise rotation around the main rotor axis, causing the tail to rise. The helicopter drifted off the edge of the helipad, lost altitude, and ultimately crashed into a cliff below the landing site. The crash resulted in 3 fatalities and the total destruction of the aircraft.
The investigation
The Taiwan Transportation Safety Board (TTSB) examined the aircraft's weight and balance, flight records, and cockpit voice recordings. The investigation focused on the aircraft's performance at high altitudes and the procedures used for loading cargo. Investigators reviewed the flight crew's actions during the final moments of the landing and analyzed the engine and rotor speed data recorded prior to the impact.
Findings
- The flight crew did not accurately calculate the aircraft's weight for the mission; ground personnel used visual estimates, and the crew did not verify the weight using scales.
- The total weight of the aircraft exceeded the maximum allowable limits for landing within ground effect at that specific altitude.
- Due to the excessive weight, the tail rotor's control margin was likely at a critical limit. When the pilot increased collective pitch to control the descent rate, the resulting increase in torque likely overwhelmed the tail rotor's ability to counteract the main rotor's torque, leading to the uncontrolled rightward yaw.
- The crew demonstrated insufficient awareness regarding the conditions that lead to tail rotor authority loss and lacked adequate training for high-altitude operations.
- There were deficiencies in the airline's safety management, including inadequate high-altitude training programs and a failure to strictly adhere to weight and balance procedures.