Incident Overview
An airplane used for skydiving operations encountered a partial loss of power during its third or fourth flight of the day due to a fuel tank vent blocked by a mud dauber nest. The pilot noted a hissing sound when a fuel cap was removed, indicating differential air pressure. Maintenance personnel cleared the vent, and the pilot resumed skydiving flights.
Sequence of Events
During the ninth flight, after skydivers had exited the aircraft at an altitude of 10,500 feet, the pilot initiated a spiraling descent to return to the airport. While on approach to land on the runway, the pilot attempted to add power to arrest the descent, but the engine did not respond. The pilot switched fuel tanks and attempted to restart the engine, but the engine remained unresponsive.
The pilot managed to fly the airplane over a pond, but the airplane touched down short of the runway threshold. To avoid a fence, the pilot steered the airplane to the left. While maneuvering between the fence and a hangar, the left wingtip struck the hangar. The airplane then pivoted into the hangar, sustaining further damage.
Post-Impact Observations
After the impact, the pilot observed that the left fuel tank had ruptured, and fuel was running onto his neck and left side. The reported temperature and dew point were 64°F and 37°F, respectively. According to icing probability charts, conditions were not conducive for carburetor icing.
Investigation Findings
No reason was found for the loss of engine power during the final approach. The earlier partial power loss had been attributed to a blocked fuel vent, but that issue had been resolved prior to the ninth flight.