What happened
On November 28, 2008, an FK 14 Polaris ultralight aircraft departed from Mühldorf-Mößling airfield for a local flight. The flight, which included the pilot and one passenger, was scheduled to return to the airfield by 16:20 local time. Radar tracking recorded the aircraft on a southbound course toward Lake Chiemsee, with the final radar contact occurring at 15:53 over the lake, east of Gstad.
After the aircraft failed to return as planned, the flight controller reported the aircraft missing. Despite search and rescue operations by the police and SAR services, no trace of the aircraft was immediately found. On January 11, 2009, the wreckage was located 57 meters below the surface of Lake Chiemsee. The aircraft was recovered on January 14, 2009. Both occupants were found restrained in their seats within the wreckage. Medical examinations determined that both occupants died due to drowning.
The investigation
The BFU examined the wreckage and the engine components. The engine, a Rotax 912 ULS, was inspected by an aviation workshop, which found no abnormalities in the spark plugs, carburetor, fuel pump, exhaust, cylinders, or ignition system. The aircraft's maintenance records showed the last annual inspection had been completed in May 2008, and the last 100-hour inspection occurred in March 2008.
Investigators also analyzed fragments of the left wing spar. The wing structure consisted of a 24 mm thick foam web between two massive unidirectional CFRP (carbon fiber reinforced plastic) caps, covered with +/- 45° CFRP laminates. The investigation noted that the cockpit canopy was extensively shattered and the fuselage had broken near the tail section.
Findings
- The aircraft's left wing spar had suffered a structural failure, with the upper spar cap splintering and the lower spar cap breaking at the wing root.
- The wreckage was found at a depth of 57 meters, with the fuselage embedded in the lakebed mud.
- The engine and its primary components were found to be in functional condition prior to the impact.