PA-18/19 Super Cub
Flight Crew Instrument; Flight Crew Rotorcraft; Flight Crew Multiengine; Maintenance Airframe; Maintenance Powerplant
Flight Crew Last 90 Days 35; Flight Crew Total 6000; Flight Crew Type 1135
Confusion; Time Pressure; Troubleshooting; Workload
Aircraft Equipment Problem Critical
Flight Crew Diverted; Flight Crew Landed in Emergency Condition; General Maintenance Action
Aircraft; Human Factors
I was flying at 4500 feet; and; had been flying for about 90 minutes. [Mid-flight]; I felt a funny vibration on my rudder pedals-my RPM was 2300. Knowing that I could have a problem; I headed West toward flat land; approximately 5 miles away. I changed fuel tanks and put on carb heat.The engine RPM started dropping slowly and at 2000 RPM; I called Approach and told them that I might have to make an off-field landing. The engine sputtered to idle and I did my emergency checklist and safely landed with no personal injuries or damage to the airplane. The airplane was towed 1.5 miles to an empty lot.The next morning; the airplane was inspected and checked by two mechanics; the A & P who performed the last annual inspection; and myself. I was given FAA permission to take off. I took off on the right fuel tank. After 5 minutes; the RPM started to fall; and I determined that I was going to have to make [a second] off-field landing. I did; and no one was injured and there was no damage to the airplane. The airplane was towed back to the empty parking lot. At that time; the four of us noticed that the left fuel tank gas cap was missing. [Two days later]; the airplane was disassembled in my presence and trucked to [the maintenance facility]. During disassembly; approximately four (4) gallons of fuel was drained from the left fuel tank and eight (8) gallons from the right fuel tank. The airplane was reassembled in my presence on [the third day]; and will be thoroughly inspected.
A Piper Super Cub pilot reported making two off field landings due to engine performance problems; possibly due to a fuel system anomaly.