Major Sydnor was the pilot of a B-26C Invader bomber with the 90th Bomber Squadron, 3rd Bomber Wing. On July 1, 1953, while on a night intruder mission, contact was lost with the aircraft after checkpoint "Oboe". He was listed as Missing in Action and was presumed dead on July 2, 1954. His remains were not recovered. His name is inscribed on the Courts of the Missing at the Honolulu Memorial.