What happened
On the afternoon of November 25, 1999, a Cosmos Hermes 16 ultralight hang glider, registration CS-UFW, departed from a private airstrip in Tojeira, Magoito, Sintra, for a local flight. During the flight, the aircraft descended into a terrain area covered in rocks and gravel used for road repairs. Witnesses reported seeing the aircraft flying at a very low altitude and noted that the engine sounded irregular before the impact. The crash resulted in the death of the pilot and the total destruction of the aircraft.
The investigation
The GPIAAF investigation examined the aircraft's engine, the pilot's credentials, and the maintenance records. Technical examination of the Rotax 503 engine revealed that while the engine was in good mechanical condition, the air filter was in poor condition, saturated with an unidentified, thick oil that was not recommended by the manufacturer. Additionally, the carburetor's mixture adjustment screw was set too closed, which caused the spark plugs to appear white, indicating a lean fuel mixture. The investigation also noted that the pilot did not possess a valid pilot's license, and there were no flight logs or maintenance records available to verify the pilot's experience or the engine's recent service history.
Findings
- The aircraft entered a nose-down attitude and lost lift, which the pilot was unable to recover from due to insufficient altitude.
- The air filter was saturated with improper oil, which likely caused a sudden loss of power or engine malfunction.
- The engine was operating with an improper fuel mixture, leading to irregular performance at low RPM.
- The pilot lacked documented training or a license, which likely hindered his ability to manage the engine emergency.
- There was a lack of documented maintenance for the engine, with no records of service since 1994.