What happened
On March 9, 2021, at approximately 09:10, an AXH-E230RS unmanned helicopter, registration B-AAA01408, crashed into the sea near the Tamsui Estuary in New Taipei City. The aircraft, operated by the Northern Branch of the Coast Guard Administration, was conducting a search and rescue mission for individuals missing after a fishing boat capsized.
The flight began at 08:51, following a planned route between Tamsui and Shalun. While the aircraft was operating in GPS mode, the ground control station (GCS) began to show abnormal attitude deviations and an inability to maintain altitude. At 0ers 09:10:00, the operator initiated the Return to Launch (RTL) mode. However, the aircraft's attitude continued to deviate sharply, and the altitude dropped rapidly. Within seconds, the data link and video feed were lost, and the aircraft impacted the water approximately 800 meters offshore.
The investigation
The Taiwan Transportation Safety Board (TTSB) examined the wreckage and flight data recorded by the flight control computer (FCC) and the GCS. Physical inspection of the wreckage revealed significant damage to the main rotor blades and swashplate components, including delamination of blade A and a broken pitch link. However, the investigation determined that this damage was a consequence of the high-impact force of hitting the water, rather than the cause of the crash.
Analysis of the flight data showed that the FCC was issuing correct Pulse-Width Modulation (PWM) commands to correct the aircraft's roll and pitch. While the flight control system attempted to execute maximum right-roll corrections to stabilize the aircraft, the physical response was absent. The investigation focused on the three main rotor servos manufactured by Tianwu Technology Co., Ltd. Upon disassembly, the servos showed signs of electrical failure; specifically, the circuit boards exhibited non-commanded movements or total inactivity when powered. While some mechanical misalignment was noted in the left servo, the primary failure was attributed to the electrical systems of the left or right servos.
Findings
- The aircraft was operating in an automated mode (RTL) at the time of the accident, and the loss of control was not due to pilot error.
- The power and propulsion systems were functioning normally prior to the impact.
- The electrical failure of the main rotor servos prevented the aircraft from executing necessary attitude corrections, leading to an uncontrollable roll and subsequent crash.
- The damage to the main rotor blades and pitch links occurred as a result of the impact with the sea surface.