Accident Summary
On February 7, 2020, at 1013 local time, a Sky Arrow 55 (SA-55) unmanned aircraft operated by GeoSat Aerospace & Technology Inc. crashed into the roof of Kaixuan Junior High School gymnasium in Yilan County, Taiwan. The aircraft was destroyed by impact and fire, and the gymnasium roof sustained minor damage. No injuries to persons on the ground were reported.
Aircraft and Operator Information
The aircraft, serial number P040, was manufactured by GeoSat Aerospace on November 29, 2019. It was a fixed-wing unmanned aircraft with a length of 2.5 meters and a wingspan of 3 meters. The operator, GeoSat Aerospace, was conducting a flight test for the Forestry Bureau's Aerial Survey Office. The external pilot had 1,120.5 total flight hours, including 13 hours 10 minutes on type. The internal pilot had 572.5 total flight hours, including 132 hours 30 minutes on type. No pilot certifications were applicable as the accident occurred before the implementation of civil aviation regulations for unmanned aircraft.
Flight and Engine Failure
The aircraft departed from the unmanned aircraft test field at National Ilan University at 0928 local time. It climbed to 220 meters and switched to automatic flight mode, then continued to 600 meters at a cruise speed of 105 km/h. At 1011:50, approximately 44 minutes after takeoff, the engine speed dropped to zero within 2 seconds. The aircraft began descending at about 5 m/s. At 1013:09, the flight mode was switched to manual. The aircraft impacted the gymnasium roof at 1013:30, about 720 meters from the ground control station (GCS). The GCS recorded data showed that after engine failure, the aircraft's speed varied between 93 and 118 km/h, not maintaining a stable glide speed. The flight control computer's fail-safe program did not automatically engage a glide return-to-field mode as stipulated in the company's manual.
Emergency Response and Procedures
The company's unmanned aircraft operations manual specified procedures for engine failure, including assessing height and distance, and either returning to the GCS or selecting a forced landing area. However, the manual did not define the best glide speed for maximum range. During the 82 seconds between engine failure and manual intervention, the internal pilot monitored parameters but did not issue a return-to-field command or select a forced landing site. The external pilot, upon switching to manual, attempted to turn the aircraft back toward the GCS, but sight lines were obstructed by trees. The aircraft's GCS system did not display critical emergency information such as distance to home, wind vector, or glide range prediction.
Conclusions
The investigation identified that the flight control computer fail-safe program was not designed to automatically enter a glide return-to-field mode after engine failure, as required by the company's manual. The operators did not follow the engine failure procedure, and the manual lacked a defined best glide speed, leading to the aircraft impacting a building. Additionally, the flight was conducted outside the approved airspace and time period, and no coordinator was stationed at air traffic control.