Flight Departure and Clearance
The air tanker N924AU departed from its base in Santa Barbara, California, at 16:05 PDT under visual flight rules (VFR), bound for Missoula, Montana, to support fire suppression efforts for large fires in the Northern Region. While still under the control of the Oakland FAA Air Route Traffic Control Center (ARTCC), the crew requested and received an Instrument Flight Rules (IFR) clearance and were assigned an altitude of 23,000 feet.
Approach to Missoula
The flight proceeded uneventfully until it was handed off to the Approach Controller at Missoula (MSO). At first contact with MSO Approach, the aircraft was 26 miles southeast of Missoula International Airport and descending to 12,000 feet. During exchanges between the crew and the controller, it was disclosed and confirmed that the flight crew did not have the approach plate for the published VOR-DME Bravo (B) approach, which was the procedure in use for aircraft arriving from the south. Despite this, clearance was offered and accepted, and the controller provided information as the crew began executing the VOR-DME B approach.
Weather and Conditions
At that time, cloud bases at MSO Airport were about 7,900 feet. Other aircraft making instrument approaches were descending through 8,000 feet, cancelling their IFR flight plans and making visual approaches to the airport. The Orion crew, monitoring these communications on the same frequency, likely anticipated doing the same. Strong winds and moderate to severe turbulence were reported at altitudes above 8,000 feet, increasing with altitude in the MSO area. Additionally, the crew had been flying at high altitudes, using oxygen in an unheated and unpressurized aircraft for over two hours.
Confusion and Loss of Contact
During the initial phase of the approach, some confusion regarding the heading to fly apparently occurred, and the air tanker turned back toward the south, away from Missoula. At that point, the controller had authorized descent to 8,600 feet on an approximate heading of 200 degrees magnetic. Salt Lake City ARTCC notified MSO Approach that the aircraft was west of the course consistent with the approach procedure, and subsequently that it had disappeared from Center's radar screen. Repeated attempts to contact the crew failed. MSO Approach notified the County Sheriff's office, the Forest Service, and other agencies that the aircraft was missing and presumed down. Search and rescue efforts were unable to detect an Emergency Locator Transmitter (ELT) signal. The mishap site was located the following day.