Donald A. Hall was an engineer who is best known as the designer of the Ryan NYP Spirit of St. Louis. Hall was born in Brooklyn, New York in 1898. In 1917, Hall graduated from the Pratt Institute with a certificate in mechanical engineering. Hall worked for Curtiss Aeroplane and Motor Company beginning in 1919 before going to Douglas Aircraft in 1924. Hall later accepted the job of chief, and only full-time, engineer at Ryan Airlines where he started on January 31, 1927. A telegram arrived four days later asking if Ryan could build an airplane capable of flying nonstop from New York to Paris, France. Hall reviewed the request and replied affirmatively and on February 21, 1927, Charles Augustus Lindbergh arrived at Ryan to discuss the aircraft. After reviewing Hall's preliminary design work, a contract was finalized between Ryan and Lindbergh on February 25, 1927. The aircraft Hall designed, the Ryan NYP Spirit of St. Louis was built and ready for flight testing on April 28, 1927, a process that took place in under two weeks. On May 21, 1927, Lindbergh completed the first solo nonstop transatlantic flight in history flying in the Spirit of St. Louis.
Later, Hall designed the Ryan X-1 Doodle Bug (Mahoney-Ryan Special). After Ryan relocated to St. Louis, Missouri, Hall stayed in San Diego, California and founded his own company, Hall Aeronautical Development Company. After the Great Depression hit, Hall was forced to close his company due to financial concerns and went to work for Consolidated in 1936. During his time with the company, Hall worked as a consultant to I. M. Laddon on the design of the Consolidated B-24 Liberator. In 1949, Hall went to work for the U.S. Navy at Naval Air Station North Island where he was an engineer before being promoted to head of the helicopter branch and later head of the structures branch before retiring in 1963. Donald A. Hall died in 1968.