What happened
A helicopter was observed flying at a low altitude and low airspeed prior to the accident. Witnesses reported hearing the engine sputter before the aircraft lost control and performed a hard landing in a residential area.
The investigation
An examination of the engine revealed that two exhaust valves had stuck open because of contamination by products of combustion. While the engine manufacturer provides maintenance procedures specifically designed to prevent such an occurrence—which can result in a partial loss of power—the helicopter operator had elected not to perform the recommended procedure.
Investigators also examined the aircraft's safety restraints. The pilot's shoulder harness failed during the impact, while the passenger's harness remained intact. The failure of the pilot's harness occurred at a worn area where the strap bends over the seat back. Both shoulder harnesses were found to be missing their required cloth data tags, and the manufacturer or history of the harnesses could not be determined.
Recent maintenance records showed that the helicopter had undergone an annual inspection approximately six months prior to the accident, followed by 100-hour and 50-hour inspections. These inspections failed to identify the discrepancies regarding the shoulder harnesses.
Toxicological testing was performed on the pilot. Results showed the presence of desalkylflurazepam (an active metabolite of the sleep medication flurazepam) in the blood. Additionally, the urine contained pseudoephedrine, phenylpropanolamine, ephedrine, and salicylate, which are substances commonly found in over-the-counter cold medications.