This is a Notable Operational milestone.
The aircraft had been extensively modified from the XR-1 in an attempt to resolve the early problems in that aircraft. The flight was conducted by Jim Ray with George "Buck" Miller as co-pilot.
Source: “Dr. W. Laurence LePage, From XR-1 to Tilt-Rotor”, Jay Brian Hendrickson, Paper presented at the American Helicopter Society 61st Annual Forum, Grapevine, TX, June 1-3, 2005