What happened
During a forced landing, the airplane entered a stall and impacted trees and terrain. Prior to the accident, witnesses reported that the engine was running intermittently and experiencing roughness.
Data recovered from a global positioning system (GPS) receiver at the accident site indicated that the aircraft's ground speed was between 73.7 and 79.8 mph during the final 10 seconds of recorded flight. The stall speed for this aircraft with flaps retracted is 70 mph.
The investigation
Investigators examined fuel samples and mechanical components to identify potential issues. Post-accident fuel samples retrieved from the fuel strainer and both electric fuel pumps revealed contamination consisting of water and particulate matter. Both electric fuel pumps also contained rust, water, and particulate.
Further inspection of the carburetor revealed that the accelerator pump-well and the float bowl were contaminated with a fine particulate resembling silicon sand. This same fine particulate was found within the nozzle well and the carburetor idle tube passage.
In contrast, fuel samples taken from the fuel selector and the right main fuel cell were clear of water and debris. Additionally, a fuel sample obtained from the departure airport showed no signs of contamination or water.