CEN19LA306 · Pietenpol Sky Scout

The pilot was conducting a postmaintenance flight. Shortly after liftoff and while the airplane was in a climbing left turn, the airplane lost total engine power. The pilot reported that, about 7 seconds after liftoff he heard the engine “splutter” as it decelerated from takeoff power toward idle. He pushed the control stick forward to reduce the airplane's angle of attack, but the airplane impacted terrain in a nose-down attitude. One witness reported that, after the loss of engine power, the airplane’s left wing dropped, and the airplane entered an aerodynamic spin that continued about one-half of a rotation before the airplane impacted the ground. The airplane sustained substantial damage to the forward fuselage and engine mount during impact.

A postaccident engine examination revealed no evidence of a mechanical failure that would have resulted in the total loss of engine power. The airplane’s fuel tank cap had a cracked rubber seal that had hardened from age, and the fuel cap vent holes were small and partially obstructed by the seal. An inadequately vented fuel cap could have resulted in a negative pressure within the fuel tank and fuel starvation to the engine. Additionally, the carburetor heat flexible hose was found disconnected from the carburetor, and there was no attachment hardware present. The weather conditions at the time and location of the accident were conducive to a serious accumulation of carburetor icing with the engine at glide (descent) power.

On the basis of the available evidence, the investigation was unable to determine whether inadequate fuel tank venting or carburetor icing caused the total loss of engine power. However, after the loss of engine power, the pilot likely exceeded the airplane’s critical angle of attack, and the airplane subsequently entered an aerodynamic stall and spin from which recovery was not possible due to the airplane’s low altitude.

Verbatim NTSB analysis and probable cause from the NTSB dataset