What happened
During an operation to reposition a banner towing aircraft to another airport, the engine lost power following takeoff. Due to unsuitable terrain surrounding the departure area, the pilot's options for maneuvering were limited. While attempting a forced landing, the aircraft struck a chain link fence.
The investigation
Mechanical examination of the engine revealed low compression and air bypass occurring on all exhaust valves, along with evidence of detonation. Investigators examined the aircraft's three fuel tanks, each with a capacity of 18 gallons. Two of these tanks contained uncontaminated fuel; however, one tank contained a pink-colored, oily fuel. This specific fuel had been treated with Marvel Mystery Oil.
The FAA reported finding an empty can of Marvel Mystery Oil in the operator's trash. While the recommended ratio for this additive is 1 part oil to 100 parts fuel, the operator lacked specific instructions regarding the timing or precise ratio for application. During the investigation, the pilot, chief pilot, and manager all denied adding the substance to the fuel, and maintenance personnel also denied involvement in adding the additive.