On October 19, 1996, a Hughes 369D (registration N34CM) was involved in an aviation accident near Watkins, CO. Investigators recorded the probable cause as: The flight instructor's improper decision to attempt a hovering autorotation during gusty wind conditions. A factor was the gusty wind. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
Aircraft registered N34CM. Photo: BLM Nevada / Public domain, via Wikimedia Commons
During a hovering autorotation demonstration at 3 feet AGL, a helicopter's main rotor struck the tail boom after touchdown. The pilot cited low rotor rpm and gusty wind as common factors for the model.
Accident Details
The accident occurred during a training flight where an instructor was demonstrating autorotation techniques to a student. According to the instructor, he entered a 'hovering auto(rotation)' to runway 17 from an altitude of 3 feet above ground level (AGL) at a speed of less than 10 knots. The instructor estimated the wind to be from 170 degrees at 12 to 15 knots. However, recorded wind at Denver International Airport, located 10 miles northwest of the accident site, was from 290 degrees at 12 knots. After the helicopter touched down, the main rotor blades struck the tail boom.
Pilot's Comments
The pilot stated that this type of incident is 'a fairly common occurrence' with this particular helicopter make and model when operating under 'low rotor rpm and gusty wind.'
Manufacturer's Response
A spokesman for the helicopter manufacturer commented that if the helicopter had been landed upwind, the accident would not have occurred. He added that if gusty wind conditions were present, autorotation demonstrations should not have been attempted.
