What happened
On December 6, 2013, a Texas Helicopter Corporation M74L helicopter, registration N1001N, was performing a positioning flight near Sebring, Florida. The flight departed from a local farm field at approximately 1615 EST, destined for Sebring Regional Airport (SEF). The purpose of the flight was to transport the aircraft for maintenance, specifically to wash the helicopter and change the engine oil, following a day of aerial application services.
During the flight, a witness observed the aircraft traveling southwest at an altitude of approximately 150 feet. The helicopter was seen dipping to between 50 and 75 feet before falling straight to the ground and bursting into flames. The aircraft impacted an open sod field approximately 1.3 nautical miles west of SEF. The pilot sustained 1 fatal injury.
The investigation
Investigators examined the wreckage and found the cockpit and various components were heavily damaged by fire. The engine's carburetor float bowl was found to be empty of fuel and contained a rust-colored powder consisting of aluminum, iron, chromium, lead, vanadium, and zinc.
Examination of the fuel truck used to service the helicopter prior to the flight revealed similar contamination in its fuel filter, hose, and pump. During a post-accident demonstration, the ground handler showed that the fuel initially dispensed from the truck was brown and gold in color, only turning blue after several gallons had been flowed through the system.
While the exact level of fuel contamination in the aircraft's tanks could not be determined due to the fire, the presence of the metallic powder in the carburetor suggested a significant loss of engine power.
Additionally, toxicology results for the pilot showed levels of diphenhydramine, a sedating antihistamine, in the blood and urine. While the levels might have been redistributed post-mortem, the presence of the drug was noted alongside the investigation into the pilot's performance.