The pilot, who was also the builder/owner of the Zenith CH-750, 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 he was unable to restart the engine.
He conducted an off-airport, forced landing near Venus, Florida, and the airplane hit 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 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.
The National Transportation Safety Board determined the probable cause as 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 Identification: ERA14LA183
This April 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.
This does sound like an issue that would be a no go for me on the aircraft, but you have to remember Zenith is in the business of trying to make flying affordable and easy to build for everyone (something I appreciate them doing). So something such as this to save a few bucks for the builder does not surprise me. Zenith is also not new to design issues. Look up the Zodiac wing issues, the very interesting “no hinge” aileron they had for a while, the liberal use of Avex rivets, and so on. After having looked at and worked on 701s and 750s in my opinion they are limited life airframes that I would never want to take anywhere near VNE or stress more than 1.7 Gs on.
Note I am not an expert in this field and my opinions should only be taken as opinion and not fact. 🙂
This poor design allows the cap with the lower opening vacuum to vent, allowing only that tank to feed fuel.
A better design would be to run both fuel lines down to the selector and gascolator, preferable near the floor. This ensures that each tank has enough fuel head pressure to open the vent on its tank..
Cessna has used this design for 50+ years. The Cessna that I fly has never run a tank dry, running on ‘both’, with the fuel selector on the floor between the seats.
We recently had a fatal accident here where a 172 pilot ran out of gas on final with fuel selector on both. Both option works fine till you run out of gas then you don’t know which one to select. He had fuel remaining in left tank. I suspect you’ve noticed on your airplane when you fill it up that both tanks seldom take the same amount of fuel.
Run on individual tanks, R L R L for 30 mins each and don’t select BOTH. Problems solved.
That would solve the in air issue for the pilot, but not the design issue of the fuel venting system or the fuel selector allowing someone to choose the both option.
Sounds like Zenith has a problem to solve, one that should have been resolved when the first incident was reported.