What happened
On 26 August 2011, an Ikarus C 42 B ultralight aircraft, registration OH-U478, performed a forced landing in a field near Hyvinkää. The flight was a training mission originating from Helsinki-Malmi, intended to provide a student pilot with several practice landings at Hyvinkää aerodrome.
During the second landing approach, while on the downwind leg at approximately 160 meters altitude, the engine RPM suddenly dropped to idle despite the power lever remaining in the cruise power position. The flight instructor took control of the aircraft as the engine stopped within seconds. Realizing the aircraft could not reach the aerodrome, the instructor steered the plane toward nearby fields, executing a successful emergency landing. There were no injuries to the instructor or the student pilot, and the aircraft sustained no damage.
The investigation
Investigators examined the engine and fuel system following the incident. While initial visual inspections and test runs were normal, subsequent testing revealed intermittent malfunctions in both ignition circuits. The electronic modules were sent to authorities in Germany and Austria for specialized analysis, where X-ray imaging revealed insufficient solder in the connections of the A-unit.
Further investigation into the aircraft's history revealed that approximately 100 flight hours prior to the accident, the engine had failed to restart during taxiing. Upon inspection of the fuel system, investigators discovered that the mechanical fuel pump's suction valve cover had shifted from its correct position over the intake port. This misalignment caused the pump to provide inconsistent pressure, evidenced by lateral scoring on the valve cover.
Findings
- The primary cause of the engine failure was a malfunction of the mechanical fuel pump's suction valve, which led to interrupted fuel delivery to the carburetors.
- A contributing factor was the low fuel pressure provided by the electric pump.
- The aircraft's fuel system design deviated significantly from the engine manufacturer's specifications, notably lacking a strainer, a fuel vapor vent, and a check valve in the electric pump bypass line.
- The investigation also noted that required reports regarding previous engine malfunctions had not been filed by the instructor.