1952 Washington, D.C. UFO incident
The 1952 Washington , D . C . UFO incident , also known as the Washington flap , the Washington National Airport Sightings , or the Invasion of Washington , was a series of unidentified flying object reports from July 12 to July 29 , 1952 , over Washington , D . C . 
<triplet> 1952 Washington, D.C. UFO incident <subj> unidentified flying object <obj> instance of