What happened
On May 2, 1999, a Comco FOX C 22 ultralight aircraft departed from runway 05 L at Lelystad airport for a scheduled training flight. Shortly after takeoff, at an altitude of approximately 25 meters, the engine power suddenly dropped to idle. The student pilot, who was operating the aircraft from the left seat, identified that the throttle cable had snapped.
Upon realizing the failure, the instructor took control of the aircraft and initiated a glide. The instructor attempted to maintain a straight flight path to land on the other side of a provincial road located near the airfield. However, the aircraft's path was obstructed by a wide ditch that had recently been excavated, followed by an earthen embankment roughly one meter high. The aircraft was unable to clear the ditch and struck the embankment, coming to an abrupt stop with part of the airframe submerged in water. The impact resulted in two serious injuries to the occupants.
The investigation
The investigation focused on the mechanical failure of the throttle system. While the student had performed a preflight inspection, investigators noted that a visual inspection of the throttle system is limited to the external cables; the internal condition of the cables cannot be verified without disassembly. During the preflight run-up, the engine appeared to respond normally to throttle inputs.
Technical examination revealed that the connection between the throttle lever and the carburetors had been severed. Specifically, a solder joint at the junction where the single throttle cable meets the distribution block—which splits the signal to the two separate carburetor cables—had failed. Because the carburetor slides are held in the idle position by spring tension, the breakage caused the engine to revert to minimum power immediately.
Findings
- The engine power loss was caused by a failure in the throttle control system due to a broken solder connection at the distribution block.
- The sudden loss of power occurred at a low altitude, leaving insufficient distance to navigate obstacles.
- The aircraft was unable to clear a wide ditch and an earthen embankment following the engine failure.
- The mechanical failure was difficult to detect during standard preflight inspections as the internal integrity of the solder joint is not visible externally.