Accident
On July 24, 2008, at approximately 0652 central daylight time, a Bell 47G-4A helicopter, registration N24HM, was involved in an accident near Mayville, Wisconsin. The pilot had shut down the engine after landing and exited the helicopter to inspect it. While the main rotor blades were still rotating, the pilot was struck by the blades and sustained fatal injuries. The flight was conducted under 14 CFR Part 137 as an agricultural application flight and was not operating on a flight plan. Visual meteorological conditions prevailed at the time.
According to a ground loader, the helicopter engine ran rough when it took off next to the field intended for spraying. The helicopter flew approximately 200 yards south before landing. During the landing, the left skid became entangled in vegetation, causing the helicopter to turn north and break off the left skid. The helicopter came to rest in a field about 3/8 mile from the loading site, leaning to the left. The pilot then exited and walked around the helicopter with the main rotor blades still rotating, leading to the fatal injury.
Aircraft Information
The helicopter was powered by a Lycoming VO-540-B1B3 engine, serial number L-2450-43, with a total time in service of 3,378.6 hours and a time since overhaul of 395 hours. No markings identified all cylinder heads and barrels as Parts Manufacturer Approval (PMA) parts, and the return-to-service tags for the engine cylinder assemblies were not received by the National Transportation Safety Board or Federal Aviation Administration.
Textron Lycoming Mandatory Service Bulletin 388 calls for 300-hour interval inspections if engine valve sticking is suspected. Engine Components, Inc. (ECI) Service Instruction 03-11, which references the same bulletin, also calls for similar inspections on ECI Titan Cylinder assemblies. No engine logbook entries indicated that such inspections had been performed.
The helicopter's maximum gross weight was 3,200 lbs, and the operator reported a weight of 3,100 lbs at the time of the accident. The helicopter was loaded with 80 lbs of chemical applicant.
Medical and Pathological Information
An autopsy of the pilot was conducted by the Dodge County Medical Examiner on July 24, 2008. The cause of death was listed as blunt force trauma. The FAA's Final Forensic Toxicology Fatal Accident Report on the pilot stated that no carbon monoxide, cyanide, or ethanol was detected in the blood. Metoprolol was detected in blood and urine, and naproxen was detected in urine.
Tests and Research
A compression check of the engine revealed that the number one cylinder had a compression ratio of 45/80 with an exhaust valve leak. The number one cylinder assembly contained a Superior Air Parts, Inc. Nimonic exhaust valve, part number SL16470AK, and an Engine Components, Inc. (ECI) exhaust valve guide, part number AEL 75838 P030. The exhaust valve exhibited four fractures and a burnt appearance. The valve guide showed excessive wear (bell-mouthing). The exhaust valve had an outside diameter of 0.496 inch; the exhaust valve guide interior diameter was 0.540 inch, resulting in a clearance of 0.044 inch compared to a nominal 0.006 inch.
Comparative examination of the number three cylinder exhaust valve also showed a burnt and worn appearance, though to a lesser degree than the number one cylinder. No visible cracks of the exhaust valve were noted.