History of the Flight
On 10 October 2007 at approximately 14:20 LT, a Van's RV-9 (HB-YML) took off from runway 03 of Kägiswil aerodrome. The pilot, a Swiss citizen born in 1932 holding a Private Pilot's Licence (A), reported the engine running well at 2600 rpm and 26.5 in-Hg boost pressure during take-off. Two independent witnesses located near the beginning of runway 03 noticed unusual engine noises.
According to the pilot's statement, after lift-off, between 50 and 100 m above ground, a power drop occurred simultaneously with high-frequency engine vibrations. Adjustments to mixture, power, and propeller settings did not improve the situation. The pilot maintained horizontal flight for about 20 seconds and initiated a left turn to return for landing via a low circuit. During the turn, engine power dropped to zero and the engine windmilled. The pilot did not attempt a restart, concentrating on an emergency landing. He switched off the master, alternator, and ignition. While turning toward the aerodrome, he was close to the ground and executed a forced landing to avoid a large building. The aircraft collided with terrain about 75 m before the building, then struck parked cars and a garage building. The landing gear, wingtips, and tail were torn off. No fire broke out despite fuel leakage. The pilot, wearing his belt, sustained minor injuries and was taken to hospital for observation.
Pre-Flight and Maintenance History
The aircraft HB-YML was a homebuilt Van's RV-9, constructed by the owner. It had a provisional airworthiness certificate issued on 29 August 2007. The aircraft had accumulated 33:02 operating hours. During the test flight phase, the builder performed work on the fuel system, including tightening locknuts due to a fuel smell in the cabin, and dismantling the purge valve on 18 September 2007. The fuel filter was removed and refitted at least once for cleanliness checks.
On 2 October 2007, the same pilot (serving as the flight adviser for the builder) experienced rough engine running during a solo flight in HB-YML. The pilot returned to Kägiswil and landed immediately. A static test run after landing showed rough engine running at 20 in-Hg and 2000 rpm.
On 6 October 2007, the builder checked the fuel filter and found it clean. A static test run produced normal engine values. On the morning of the accident, 10 October, the builder changed the spark plug gap from 0.75 mm to 0.6 mm on advice, then performed two static test runs with normal results.
Meteorological Information
Meteorological reports from Alpnach aerodrome (5 km north) indicated wind from 050° at 13 kt at 13:50 LT. At 14:25 LT, the Alpnach controller reported wind strength 16 kt from the north.
Aircraft and Damage
The aircraft was a Van's RV-9, serial number 91100, with empty weight 515.1 kg and maximum take-off mass 795.0 kg. It was powered by an Aero Sport Power IO-320-D1A engine (156 HP at 2600 rpm) with a Hartzell HC-C2YL-1BF variable pitch propeller. The aircraft was destroyed. Serious damage to buildings and material occurred on the ground.