Accident Summary
During cruise flight, the helicopter's engine lost power and the pilot could not restore it. The forced landing occurred in darkness, hindering the pilot's ability to see the terrain, and the helicopter struck the ground hard.
Engine Examination
Examination of the engine found that two lower screws of the No. 3 valve cover were missing. The attachment bolts of the intake pipes for both the No. 1 and No. 3 cylinder assemblies were loose. The No. 3 intake pipe was rotated approximately 180 degrees from its normally installed position. Gaskets that are typically installed under the intake pipe flanges of the No. 1 and No. 3 intake pipes were absent. The No. 1, No. 2, and No. 4 spark plugs were wet with fuel, while the No. 3 spark plug was dry and displayed tan-colored combustion deposits.
Maintenance Records
A review of maintenance records showed that the engine had operated 38.2 hours since its most recent inspection.