United Airlines Trip 4 was a Boeing 247D operating on a scheduled flight from Salt Lake City, Utah, to Cheyenne, Wyoming, on October 7, 1935. The aircraft last contacted Cheyenne at 2:16 or 2:17 a.m. reporting its position as Silver Crown. Cheyenne called the flight at 2:17, receiving no reply. The weather was virtually clear with ceiling unlimited. The pilot was believed to be flying on instruments. The probable cause was determined to be pilot error in failing to monitor altitude or location.