In 1939, at age seven, John received his first flight instruction in a Stinson SR9B Reliant, while sitting on his father's lap to reach the controls.
(He would later base his personal plane there, until the airfield's closure, later writing two books about it, and then serving as a key consultant and resource for the terminal's historic restoration and commemoration.
)[5][7][8] In 1949, at age 17, Underwood learned to fly at the Glendale School of Aeronautics, while working for Grand Central Aircraft, refurbishing surplus World War II aircraft, including (North American P-51 Mustang fighters, Curtiss-Wright C-46 Commando transports, and North American B-25 Mitchell bombers.
[1][3][2][10][9] Underwood is believed to have been a member of the International Amateur Aircraft Photographers Exchange (IAAPE), a 1930s-era group who developed a significant collection of historical aviation images.
[7][9] Underwood became a principal aviation history author, consultant and photo-supplier for the journals of the AAHS[3][7][14] and the Vintage Aircraft Association (of the EAA).