Accident Summary
A training flight ended with the airplane colliding with trees during a forced landing after the engine lost power. The flight had involved maneuvering in a local practice area for over 30 minutes. During a climb, the certificated flight instructor (CFI) observed that the engine's revolutions per minute (rpm) were low. The student pilot then slightly retarded the throttle and propeller controls, after which the engine surged and subsequently quit.
Engine Power Loss and Forced Landing
Following the power loss, the CFI configured the airplane for a forced landing at a private dirt airstrip. At the time, the fuel quantity gauges indicated the right tank had 1/4 fuel remaining and the left tank showed 1/2 fuel remaining. As the airplane descended to about 10 to 15 feet above ground level (AGL), it encountered a crosswind followed by a sudden tailwind. The airplane then collided with trees adjacent to the airstrip.
Post-Accident Examination
After recovery from the accident site, a post-accident examination of the engine revealed no evidence of preimpact mechanical malfunction or failure that would have precluded normal operation. Investigators removed and inspected the fuel bladders by cutting open the cell along the outer wall. The left bladder, manufactured in 1958, exhibited several distinct wrinkles peaking about 1-inch high at the most creased area. Significant creases were situated near the fuel pick up and stretched along the cord line about 29 inches in length. The fuel sending unit roller rested on one of the smaller crease about .6 inches tall.
Fuel Bladder Condition
An airworthiness directive (AD) had been issued in 1986 to prevent power loss or engine stoppage due to contamination of fuel system from water and debris trapped by fuel bladder wrinkles. The aircraft's logbook indicated that the AD was complied with in 1988.