Primary finding
Probable cause
The pilot's abrupt (improper) control action which resulted in the main rotor contacting the tail boom. Contributing factors were the false indication provided by the engine tachometer, the pilot's decision to immediately initiate an autorotation instead of performing a precautionary landing, and the corn field encountered during landing.
Investigator assessment
Analysis narrative
The pilot reported that the amateur-built helicopter was in cruise flight at 1,750 feet mean sea level when the main rotor contacted the tail boom. He stated that the engine tachometer began indicating near the high operating limit. At the same time the rotor tachometer was indicating near the low operating limit. His attempt to correct the condition was not successful. The pilot stated that he lowered the collective and the helicopter pitched forward. He reported that when he compensated for the forward pitch the main rotor blades struck the tail boom. He then turned into the wind and entered an autorotation. The pilot stated that a post accident examination revealed that the engine tachometer was providing false indications and improperly indicated an engine overspeed condition.
Source record
Factual narrative
This report is based on information received by the NTSB. Additional details may be found in the NTSB's public docket for this case. For further information, please contact the NTSB Office of Public Inquiries.