This is a Significant Operational milestone.
The XV-15 Tilt Rotor Research Aircraft (TRRA) was a joint NASA/U.S. Army/Bell Helicopter program to demonstrate the benefits of the tilt rotor concept. Pilots for the first flight were Ron Erhart and Dorman Cannon. The first flight was conducted by Ship 1 (N702NA). Only two aircraft were built (Ship 1 - N702NA and Ship 2 - N703NA). The XV-15 TRRA program ran for 26 years.
The aircraft was also known by the company designation Bell 301.
See AHS Calendar May 2012 for more details.
Source: 'XV-15 Makes First Hover Flight', Aviation Week & Space Technology, May 9, 1977, Page 15