What happened
On June 21, 2015, at approximately 08:36, a CGS Hawk Arrow II ultralight aircraft crashed near the Koushe River embankment in Kaohsiung, Pingtung County. The flight began at 08:17 from the Saijiajihao ultralight airfield. While the aircraft was operating within the approved airspace, the pilot eventually deviated from the designated boundaries while flying along the Koushe River.
During the flight, the pilot discovered that the ailerons had become unresponsive. Attempting to manage the aircraft using engine thrust and rudder inputs, the pilot attempted an emergency landing on a grassy area near the river embankment. However, the aircraft entered a steep spiral descent, with the descent rate reaching 1,200 feet per minute and airspeed increasing to 90 mph, before impacting the ground at a high bank angle. The aircraft was destroyed, and the pilot sustained two fractured legs and a forehead laceration.
The investigation
The investigation focused on the mechanical failure of the control system and the regulatory status of the flight. Investigators examined the wreckage and found significant damage to the cockpit, landing gear, and the left wing leading edge.
Laboratory analysis of the aileron control linkage revealed that the component, which connects the control cables to the control stick, had suffered severe internal and external corrosion. Microscopic examination showed that the corrosion had penetrated approximately two-thirds of the tube wall thickness. This structural degradation left the remaining metal unable to withstand the aerodynamic loads experienced during flight, leading to the eventual fracture.
Additionally, the investigation confirmed that the pilot was operating without a valid ultralight aircraft pilot certificate and that the CGS Hawk Arrow II had not undergone required inspections or received a certificate of airworthiness. The aircraft had been assembled by the pilot and stored at an association warehouse prior to the flight.
Findings
- The primary cause of the accident was the failure of the aileron control linkage due to severe corrosion, which rendered the ailerons inoperable.
- The pilot's subsequent control inputs, specifically the use of heavy rudder input, induced a spiral descent that could not be recovered.
- The pilot was operating the aircraft without the required pilot certification.
- The aircraft was being operated without a valid certificate of airworthiness.
- The flight deviated from the authorized airspace boundaries.