Incident Description
The aircraft was in cruise flight at 7500 feet when the engine RPM began to decrease. The pilot remarked that the situation was like running out of gas. The aircraft subsequently collided with a wooden powerline pole during a forced landing at night. After the collision, the aircraft came to rest inverted.
Investigation Findings
Post-incident examination revealed approximately 20 gallons of red aviation gasoline in the right fuel tank and about 1 gallon in the left tank. About 3 ounces of liquid were drained from the carburetor; analysis concluded that the majority of this liquid was water.
Maintenance records indicated that wing tank sump drains had been installed in May 1983. An airworthiness directive (AD) addressing water contamination of the fuel system caused by wrinkles or folds in the tank bladders had been signed off in September 1984. The mechanic who performed that work was contacted and stated that he found no wrinkles that would justify installation of the Cessna drain kit described in Service Letter SE84-9. However, examination of the bladder tanks revealed wrinkles and folds in the vicinity of both outlets feeding fuel to the engine.