Dova Aircraft DV-1 N919E accident near San Carlos, California

Probable cause

A partial loss of engine power due to fuel vapor lock. Contributing to the accident was the absence of a fuel return line.

NTSB analysis

The sport pilot had flown the special light-sport airplane to the airport earlier in the day and refueled. During his first departure attempt, the engine began to operate roughly, and he aborted the takeoff. After another departure attempt with the same results, he aborted the takeoff and taxied the airplane to a mechanic, who suggested that the airplane was experiencing vapor lock in the fuel system and that he let the engine cool down. The pilot waited and then performed an engine run-up, which appeared normal. He reattempted the departure, but the engine experienced a partial loss of power as the airplane began to climb through 50 to 75 ft. The pilot pitched the airplane down into a nose-low configuration and crashed into a field.

Postaccident engine examination did not revealed any evidence of preimpact mechanical malfunctions or failures that would have precluded normal operation. Examination of the fuel system revealed that the airplane was not equipped with a mandatory fuel return line, although specified in the engine manufacturer's installation instructions. Manufacturer guidance indicated that the return line prevents malfunctions caused by the formation of vapor lock.

A combination electronic flight instrument system and engine monitoring system was installed in the airplane, and the data was downloaded from the unit after the examination. The data showed that during the presumed accident takeoff, the fuel level in one tank was between 0 and .05 gallons and the other was at 10.4 gallons and decreasing. During this time, the fuel flow fluctuated between 1 and 7.1 pounds per square inch, which was consistent with the system containing air bubbles and, with the fuel system not being equipped with any way to vent that air, indicative that a vapor lock scenario was imminent. It is likely that the absence of the fuel return line resulted in the engine losing power due to vapor lock.

Text from the NTSB. Open the NTSB docket for WPR15LA251 for the full record.