I was about halfway through my phase one flight-test program for the Zenith Zodiac 601XL experimental I built. The plane carries 30 gallons of fuel in two 15-gallon wing-mounted tanks. With the dihedral in the wings and the tanks half-full, I can see fuel at the outboard corner of the tank when looking through the filler neck. I clearly remember noting half-full tanks during my preflight inspection, which was confirmed once I turned on the avionics, which reports in tenths of a gallon.
Once I started the engine and made it to the runup area, the Dynon D-180 registered about 10 gallons in the selected right tank (I have a Lycoming O-235-L2C engine installed and typically I burn about 5-6 gallons an hour). I thought it was peculiar, but I attributed the loss of five gallons to starting, taxi and runup. I took off and headed the 30 miles to my practice area. At 90 mph, it usually takes about 20 minutes.
Before continuing my flight test profile, I rechecked fuel and noticed I was now down to four gallons in the right tank. A bit shocked, I attributed this to the fuel sloshing in the tank or a bad sender. Either way, I switched to the left tank and did a few turns to clear the practice area, three or four minutes later, the left tank was reading 10 gallons. Clearly there was a problem, but I just couldn’t believe it. Where the hell was my fuel going? I didn’t smell gas and there was nothing flowing around my feet. Either way, it was time to head home and figure it out.
By the time I got back to the airplane’s base, I had two gallons in the left tank and 1.5 in the right. I should have declared an emergency but didn’t. I guess I was afraid that anyone listening would assume that my emergency was of my own manufacture by not properly planning my flight. That was a mistake that I will never make again. I did sit in the cockpit for about 10 minutes until my knees stopped shaking. To say that I had a bit of a pucker factor would be a bit of an understatement!
The problem was quickly found with the help of a friend (and five gallons of 100LL). When I built the plane, I installed braided stainless steel-covered fuel lines. The line from the engine driven fuel pump to the carb inlet was leaking, and not from the fitting: The rubber line under the braiding had a hole in it. Once I pressurized the line by turning on the electric fuel pump, fuel sprayed out of the perforated fuel line and directly onto the exhaust stack. Quite a humbling experience. Needless to say, I quickly replaced the line later that day.
My CFI made sure that I always scan the ground for an emergency landing area…I did that day, but thankfully I didn’t have to walk home.