What happened
On January 20, 2015, a Piper PA-28-140, registration N4666R, experienced a loss of engine power shortly after departing Helena Regional Airport (HLN) in Montana. The flight was being operated as a personal flight under 14 CFR Part 91, destined for Missoula, Montana, under visual meteorological conditions.
During the takeoff roll, the aircraft rotated at 65 mph. The pilot reported that during the initial climb, the engine was not developing full power. At an altitude of approximately 350 to 400 feet, the pilot attempted a shallow left turn to return to the airport. During this maneuver, the aircraft failed to maintain airspeed or altitude, resulting in a collision with a house. The aircraft also struck power lines, a tree, and a propane tank before coming to rest in a shed and an adjacent house.
The pilot was not injured, while the passenger sustained minor injuries. The aircraft sustained substantial damage, including the separation of both wings from the airframe.
The investigation
An engine inspection conducted in April 2015 under FAA supervision found no obvious external damage to the engine. The engine remained attached to the engine mount and the airframe. Investigators found that the fuel strainer screen, electric fuel pump screen, and air filter were free of obstructions. Manual rotation of the engine showed compression in all cylinders, and the magneto-to-engine timing was within manufacturer specifications. However, testing revealed that two spark plugs failed to fire.
While the carburetor appeared to function normally during testing, investigators noted the absence of a retaining cotter pin and found partial soot in the throat area. The carburetor bowl was empty. Additionally, although the fuel selector was set to the right tank, the right main fuel tank was found to be empty.