On November 10, 1986, a Bell 47G-3B-1 (registration N47042) was involved in an aviation accident near Goshen, UT. Investigators recorded the probable cause as: the pilot's failure to maintain adequate main rotor RPM during the approach and his subsequent application of aft cyclic after a hard landing, which caused the main rotor to strike the tail boom. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter sustained substantial damage when the pilot allowed rotor RPM to decay during a power-off full-stop autorotation, resulting in a hard landing and rollover.
What happened
The pilot was conducting flight training maneuvers involving power recovery autorotations. Following this practice, the pilot attempted a power-off, full-stop autorotation. During the approach phase of this maneuver, the main rotor RPM decayed significantly. The pilot did not take corrective action to maintain the required rotor speed.
The aircraft landed hard with slight forward motion. Upon impact, the pilot applied aft cyclic control input. This action caused the main rotor blades to strike the tail boom. The force of the impact caused the helicopter to roll over onto its right side.
The investigation
The physical evidence indicated that the main rotor had struck the tail boom during the post-landing sequence. The rollover occurred on the right side, consistent with the application of aft cyclic following a hard landing.
Probable cause
the pilot's failure to maintain adequate main rotor RPM during the approach and his subsequent application of aft cyclic after a hard landing, which caused the main rotor to strike the tail boom.