On August 5, 1999, a Robinson R-22A (registration N8561K) was involved in an aviation accident near Shirley, NY. Investigators recorded the probable cause as: The instructor pilot's improper execution of the autorotation maneuver, which resulted in a loss of main rotor RPM and subsequent rapid descent. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter crashed during a training exercise when the main rotor RPM dropped during flare, causing a rapid descent and inverted impact.
What happened
The accident occurred during a flight training session involving an instructor pilot and a student pilot. The instructor was demonstrating a 180-degree autorotation maneuver to the student. According to the certified flight instructor (CFI), the helicopter's main rotor RPM dropped immediately after the initiation of the flare phase of the maneuver. This loss of rotational energy caused the helicopter to fall rapidly toward the ground.
Upon impact with the surface, the helicopter bounced before coming to rest in an inverted position. Post-accident inspection revealed no reported mechanical malfunctions of the airframe or engine by the pilot prior to the event.
The investigation
Examination of the aircraft following the crash showed that it had come to rest upside down after bouncing upon impact. The pilot did not report any mechanical issues with the airframe or engine before the incident occurred.
Probable cause
The instructor pilot's improper execution of the autorotation maneuver, which resulted in a loss of main rotor RPM and subsequent rapid descent.