What happened
On January 13, 2006, at 16:35, a Quicksilver Sport 2S ultralight aircraft departed from a flying site in Zhongpu, Chiayi. While performing a low-altitude flight near Renyi Pond, the pilot attempted to climb to clear rising terrain. During this maneuver, the engine RPM decreased, and the engine subsequently failed during a turn. In an attempt to avoid obstacles, the pilot maneuvered toward a betel nut plantation, but the aircraft's right wing struck a tree, causing the aircraft to crash into an orchard near Renyi Pond. The pilot sustained no injuries, though the aircraft suffered substantial damage, including a bent left wing, a deformed support structure, and a damaged tail.
The investigation
The investigation focused on the mechanical state of the ROTAX 582 engine and the regulatory compliance of the flight. Physical examination of the engine revealed that the crankshaft had seized. Investigators found evidence of extreme overheating in the cylinder head and piston of the second cylinder, characterized by a grayish-white appearance. The crankshaft was found to be laterally deflected, causing the connecting rod to strike the bottom of the crankcase, resulting in a visible fracture that penetrated to the exterior. Furthermore, the investigation found that the engine's bearing rollers had melted and deformed. Metal fragments from a broken copper washer were discovered in the intake rotary valve, which had caused the intake to seize and the engine to stall.
Maintenance records were found to be non-existent. While the aircraft owner stated that periodic maintenance was performed, there were no logs to verify this. Specifically, the replacement of the fuel filter and the engine oil was overdue by 135 hours, and spark plug replacement was overdue by 10 hours. Additionally, the investigation revealed that the pilot was operating with an expired ultralight certificate and was not flying within a legally approved airspace or using a certified flying site.
Findings
- The primary cause of the engine failure was abnormal combustion in the second cylinder, which led to the deformation of the crankshaft and the subsequent failure of the bearing and intake mechanism.
- The engine's intake rotary valve seized due to copper debris from a broken washer being drawn into the system.
- Maintenance of the lubrication system, including the oil pump and filter, was not performed according to the manufacturer's required intervals.
- The pilot failed to monitor essential engine instruments, such as RPM and temperature gauges, and was unaware of the aircraft's specific performance limitations, including stall speed.
- The flight was conducted in an unauthorized airspace using an uncertified flying site, as the site lacked proper approval from land management authorities and the Civil Aviation Administration.