Staff Sgt. Mason Johnson uses a cornice brake to bend a seal retainer. U.S. Air Force Staff Sgt. Mason Johnson, an aircraft structural maintenance craftsman with the 28th Maintenance Squadron, uses a cornice brake to bend a seal retainer at Ellsworth Air Force Base, S.D., on Feb. 26, 2009. Structural maintainers use metalworking equipment and tools to manipulate replacement parts for damaged structures and components of aircraft. SHARE IMAGE: Download Image: Full Size (0.06 MB) Photo By: VIRIN: 767158-C-NTZ42-470.jpg Photo Gallery