United Air Lines Flight 4

United Air Lines Flight 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 02:16 or 02:17, reporting its position as Silver Crown. Cheyenne called the flight at 02:21, receiving no reply. The weather was virtually clear with ceiling unlimited.

The wreckage was located 3 mi (4.8 km) east of Silver Crown. The aircraft struck the ground in a shallow descent just below a small knoll. Marks on the ground made by the propellers, fuselage, and engine showed the aircraft was in a normal flight attitude. Propeller marks and engine damage established the engines were developing normal power and the aircraft was at cruising speed. An untouched knoll 60 ft (18 m) further back on the flight path and 3 ft (0.9 m) higher established that the aircraft was descending.

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.