 On September 19, 1957, during a flight between San Francisco and Honolulu, the crew heard a loud noise, described as "similar to dropping the navigation stool on the flight deck".In-flight inspections were performed and the plane landed without incident after the crew found no abnormalities.A company inspector later investigated and found nothing out of the ordinary, noting in his report "... you could duplicate loud noise by stepping hard on door between cockpit and cargo.