Amateur-built ZENITH CH 750 N938VP accident near Venus, Florida

Probable cause

The fuel system’s inadequate design, which resulted in negative pressure in the right fuel tank and a total loss of engine power during cruise flight due to fuel starvation.

NTSB analysis

The pilot, who was also the builder/owner of the kit airplane, reported that he was en route toward his home airport with each wing tank about 3/4 full. About 50 minutes into the flight, the engine experienced a total loss of power, and the pilot was unable to restart the engine. The pilot conducted an off-airport, forced landing, and the airplane impacted vegetation and came to rest inverted, which resulted in substantial damage to the left wing, vertical stabilizer, and nose structure.

After the airplane came to rest, the pilot turned the fuel selector valve to the "off" position. Examination of the airplane revealed that the left wing fuel tank was devoid of fuel and that the right wing fuel tank contained about 6 gallons of fuel. Further examination revealed that, when the fuel line to the carburetor was removed and the fuel selector was selected to the "on" position, fuel drained freely from the fuel tank. Examination of both fuel tank venting caps revealed no abnormalities that would have precluded normal operation.

According to the fuel system drawing provided by the manufacturer, the fuel line from the right fuel tank runs laterally across the top of the airplane cabin to a T-fitting that is connected to the left tank fuel line. The fuel line then runs down the side of the airplane to the gascolator and the "on/off" shutoff valve. The airplane had no interconnecting fuel venting system, and each fuel tank was independently vented through the fuel caps.

An internet forum on this make and model kit airplane noted the occurrence of several other similar in-flight fuel starvation events. The general consensus of the forum discussion was that the fuel system design led to a partial or complete vacuum being developed during fuel consumption, which resulted in the fuel in the left fuel tank being consumed and a subsequent total power loss and in the right fuel tank being at or near maximum capacity. Therefore, it is likely that the fuel system's venting was not sufficient to provide adequate positive pressure and that this resulted in a vacuum developing between the right fuel tank and the T-fitting and the subsequent loss of engine power due to fuel starvation.

Text from the NTSB. Open the NTSB docket for ERA14LA183 for the full record.