Photograph of men installing a new engine in the Learjet 23 prototype, February 21, 1964.Inscription on verso: "Installing new engine on Jet #1 / 2-21-64."
Photograph of the Learjet 23 prototype undergoing a fuselage side-bending test, February 25, 1964.Text on sign: "Fuselage side bending static test / 0% ultimate / 25 Feb. 1964."Inscription on verso: "T58-4A / 2-25-64."
Photograph of the Learjet 23 prototype undergoing a fuselage side-bending test, February 25, 1964. Text on sign: "Fuselage side bending static test / 0% ultimate / 25 Feb. 2964."Inscription on verso: "T-58-4C / 2-25-64."
Photograph of the Learjet 23 prototype undergoing a fuselage side-bending test, February 25, 1964. Text on sign: "Fuselage side bending static test / 67% ultimate / 25 Feb. 2964."Inscription on verso: "Gene Koenig / middle white shirt / T-58-4E /…