Right: The F-16 Mid-Life Update programme is well underway, with the main changes detailed in the diagram. ... since they had to choose between the F- 16, the Saab JA37 Viggen, and the Dassault Mirage F.1E with a SNECMA M53 engine. ... The Viper and Electric Jet (because of its FBW controls) were both used informally, and Mustang II was considered. ... However, the USAF withdrew in 1992.