The pilot reported that, while in cruise flight, the FK Lightplanes FK9’s engine experienced a partial power loss. The experimental plane was unable to maintain altitude, so the pilot chose to perform an off-airport landing to an open field near Canton, Georgia. During the landing roll, the airplane hit a berm, became airborne, and then landed hard.
Examination of the engine revealed that the carburetor float chamber vent lines had been incorrectly routed to the air filter.
The engine manufacturer’s installation manual cautioned that the float chamber vent lines must not be routed into the slipstream or down the firewall because “pressure differences between the intake pressure in the carburetor chambers may lead to engine malfunction due to incorrect fuel supply.”
It is likely that the incorrectly installed vent line resulted in back pressure to the float bowl that exceeded the normal operating range, which would have affected the engine’s fuel-air mixture and led to the partial loss of engine power.
The NTSB determined the probable cause as a partial loss of engine power during cruise flight due to an overly lean fuel-air mixture, which resulted from an incorrectly installed float chamber vent line and led to a subsequent off-airport landing.
NTSB Identification: ERA14LA089
This January 2014 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.