Flight Details
The flight departed Helena at 0753 local time using Runway 29. The flight plan, amended before takeoff, specified an altitude of 10,500 feet MSL under instrument flight rules. The route followed Amber Airway Number 2 to the Whitehall (Montana) Range Station, then Red Airway Number 2 to the Butte Airport. Before takeoff, the pilot inquired with Helena Tower about the Homestake Fan and was informed that Butte Radio advised it was operating.
After takeoff, the aircraft executed a climbing right turn, passing approximately over the station as it headed south toward Whitehall. At 0801, the flight reported reaching its cruising altitude, and Helena acknowledged. The next communication was to Butte at 0814, reporting over Whitehall at 0811 and starting descent. Butte acknowledged, provided the altimeter setting of 29.97, advised winds were south and calm, and noted that the Weather Bureau indicated lower ceilings to the east and north, with better conditions to the south and southwest. Flight 115 responded that it had vertical visibility at 10,500 feet. This was the last radio contact.
Wreckage and Casualties
After several unsuccessful attempts to contact the aircraft, a search was initiated. The following morning at about 0900, wreckage was sighted from a local search aircraft. Ground parties immediately proceeded to the crash site. All debris was found in a snow-covered wooded area, and all 21 occupants were killed.
Investigation Findings
The official investigation concluded that the probable cause of the accident was the failure of the captain to conduct the flight in accordance with the prescribed approach procedure. The following findings were reported: the pilot failed to follow the carrier's prescribed Number 2 instrument approach procedure to Butte Airport, which was approved by the Civil Aeronautics Administration; the aircraft struck a mountain at approximately the 8,250-foot level while on a heading of about 290 degrees magnetic; and the accident occurred during a local snowstorm with variable ceiling and visibility.