First untethered flight of the Convair XFY-1 Pogo
Sunday, August 1, 1954
- NAS Moffett Field, United States of America 
This is a Significant Operational milestone.
Description:
The aircraft had flown, tethered, on 29 Apr 1954. The aircraft went on to complete the first successful complete VTOL transition flight.
Source: AHS Calendar August 2014 for more details
