Accident Overview
On 11 April 2009 at 15:06 local time, an AS202/15 Bravo aircraft, registered as HB-HEM, crashed into Lake Constance near Thal, Switzerland, about 1 nautical mile west of St. Gallen-Altenrhein airfield. The aircraft was destroyed and the pilot, the sole occupant, sustained serious injuries. The accident occurred during the initial climb after takeoff from runway 28.
Flight History
The pilot, a Swiss citizen born in 1941, held a private pilot license (PPL(A)) issued in 1970 and a class rating for the accident type that had expired in 1996. She had accumulated 673:21 total flight hours, with over 300 hours on type. On the day of the accident, she arrived at the airfield in the early afternoon and prepared for a sightseeing flight. After preflight checks, she started the engine and taxied to the holding point for runway 28. Engine run-up checks revealed no abnormalities. At 15:05:19, she received takeoff clearance and was advised of a south wind at 4 knots. The aircraft began its takeoff roll and lifted off.
During the initial climb, both the pilot and the air traffic controller noted that the aircraft was climbing less steeply than usual. At approximately 30 meters above ground, the engine began to stutter and then failed completely. The aircraft pitched nose-down and banked left, descending to the lake surface. Seconds later, it struck the water. The pilot was rescued by a boat crew.
Technical Findings
The accident aircraft, serial number 007, was built in 1973 and had accumulated 11,376:37 flight hours. The last annual inspection was performed on 5 February 2009 at 11,346:47 hours. After recovery from shallow water (about 90 cm deep), the wreck was examined. The fuel tanks were nearly full, and a fuel sample showed no irregularities. The tank selector was found in the right tank position, the ignition switch was set to "both", and the electric fuel pump was on. The left wing leading edge was heavily deformed, while the right wing showed only slight deformation. The propeller was slightly bent. The four-point harness was correctly fastened and had withstood the impact.
The engine was removed and subjected to a functional test and power check, showing no significant deviations and delivering required power. All accessories—carburetor, electric fuel pump, fuel lines, and tank selector—were found to be without defects. However, a defect was found in the left fuel tank: the suction pipe, fitted with a coarse filter, is normally held by a bracket with a rubber grommet to prevent metal-to-metal contact. In this case, the bracket had sawed through half of the suction pipe, and the bracket together with parts of the rubber grommet could significantly restrict the pipe's cross-section, thereby impeding fuel flow. The right tank's suction pipe also showed abrasion but was not cut through.
Probable Cause
The accident was caused by an engine power loss immediately after takeoff due to a fuel line failure. The pilot was forced to make an emergency landing on water, during which a violent impact occurred.