Accident Overview
On March 9, 2021, at 0910 local time, a Coast Guard Administration (CGA) Northern Branch unmanned helicopter, registration B-AAA01408, crashed into the sea near the Danshui River estuary in New Taipei City. The aircraft, a model AXH-E230RS manufactured by Tianwu Technology Co., Ltd., was destroyed. No injuries occurred.
The helicopter was conducting a search mission for a capsized fishing boat. It departed at 0851 from a launch site in the Tamsui District holiday flying field, operating within an area below 400 feet between Shalun and Taipei Port. The crew consisted of a team leader, observer, pilot, and lookout, all holding CAA remote pilot certificates. The pilot, aged 36, had a total flight time of 76 hours 30 minutes, with 55 hours 24 minutes on the accident type. The observer, aged 27, had 197 hours 1 minute total, with 54 hours 51 minutes on type.
Flight Sequence
The pre-planned route ran along the coast. At 0909:54, after completing the planned waypoints, the aircraft entered GPS mode. The ground control station (GCS) then showed attitude deviation and an inability to maintain altitude. At 0910:00, the pilot initiated Return to Launch (RTL) mode. The aircraft's attitude continued to deteriorate, and data transmission ceased at 0910:05. The last GCS data indicated a speed of 7 m/s, altitude 4 meters, pitch -9.8 degrees, and roll 108 degrees. The helicopter crashed into the sea approximately 800 meters offshore, about 1 kilometer from the launch point.
Investigation Findings
Flight data recorded from the flight control computer (FCC) and GCS showed normal flight until 0909:53.2, when a left roll began. The FCC output correct right-roll and collective pitch commands, but the aircraft did not respond as commanded. The left and right main rotor servos were suspected to have failed. Post-crash examination of the three servos revealed that all circuit boards were nonfunctional after immersion, exhibiting uncommanded movements or no response when powered. The left servo showed a misaligned first-stage gear, but no abnormal wear was found. The right servo gear train was normal. The main rotor components (blades, pitch links) were damaged during impact with the water, consistent with a high-energy crash.
Probable Cause
The probable cause, as stated in the official report, is that the left or right main rotor servo electrical system failed, causing the unmanned helicopter to lose control and crash.