Precautionary Landing
A helicopter pilot observed the engine oil pressure light illuminate, followed by an illuminated generator light and low rotor rpm audio. After informing passengers of a precautionary landing and briefing them on emergency procedures, the pilot entered autorotation and attempted an unsuccessful engine restart. The helicopter continued to a preselected landing zone, cleared obstacles, and landed in an open area.
A passenger seated in the back reported smelling fuel approximately 15 seconds before the low rpm audio warning. During the landing attempt, the helicopter bounced back into the air after initial touchdown and came to a sudden stop after a skid caught in a ditch.
Fuel System Inspection
On-scene examination of the fuel system revealed that the T-fitting was partially attached to the ignition solenoid housing. The safety wire was noted as not a field installation. Maintenance personnel indicated no fieldwork had been performed in that area, and the last overhaul occurred at the manufacturer's facility in June 1999.
Engine Examination
The engine was later examined at the manufacturer's facility. Before removing the ignition solenoid valve, T-fitting, and start drain components, manufacturer representatives confirmed that the safety wire (a swedged unit) was installed during the last overhaul. Visual inspection showed both the T-fitting and ignition solenoid valve threads covered in a black substance with metallic particles. The O-ring on the T-fitting was flattened with material missing. The T-fitting is steel; the ignition solenoid valve is aluminum alloy; the O-ring sits in a recessed groove providing sealing between the threaded portions.
Energy dispersive x-ray spectroscopy (EDS) indicated the black substance contained peaks of aluminum. The inside threaded portion of the solenoid valve housing exhibited deterioration consistent with fretting. Examination of the chamfer area (the recessed groove guiding the O-ring) showed it was outside the manufacturer's design specifications. The O-ring would not have seated properly due to the abnormal chamfer, preventing adequate clamping forces and potentially allowing the lock nut to loosen.
Engine Test
After reassembly, the engine was placed in a test cell for an acceptance run. It started and ran for approximately 20 minutes while conducting a range of acceptance tests. No discrepancies were noted during the engine run-up.