After several years of Boeing flight test work, PA099 was placed in storage by Boeing for several years, until sold to the U.S. Government - National Aeronautics and Space Administration (NASA) as a flight test airplane on July 26, 1973. It had accumulated only 979 flying hours. . NASA had two blue and white color schemes over the life of the airplane. Their call sign was simply NASA 515. As a public use airplane, PA099 voluntarily became N515NA on the FAA registry.
NASA 515 was involved in numerous pioneering flight investigations including control systems, 3D and 4D navigation, in-flight energy management, computerized flight management systems, electronic displays, Microwave Landing System (MLS) development (overrun in late development by the advent of GPS,), slippery runway studies, and clear air turbulence and wind shear detection and warning.
has a second flight deck, fully functional, installed in the main
that was used for much of the flying. Control systems used
the original Boeing control column/wheel, Brolly handles (like bicycle
handlebars), and the current side-stick controllers. Numerous
cockpit CRT display configurations were tried, that attacked many
regarding display arrangements, colors and symbology.
work wound up on Boeing, Douglas, and Airbus airplanes as well as the
Shuttle. The airplane has a unique fourth hydraulic system
reservoir, pump and filter system.
Other studies were
drag-reducing external coatings, cockpit displayed traffic information,
performance monitoring, and precision flare guidance (during landing
For a superb in-depth discussion of all these flight test studies, and many more, please refer to the outstanding book Airborne Trailblazer, written by Lane Wallace and released by NASA. This book is entirely devoted to the NASA flight tests performed using this historic aircraft, and it is available for reading on-line here.