What happened
On a flight dispatched from Santa Barbara, California, to assist with fire suppression in Montana, the Orion air tanker, registration N924AU, transitioned from visual flight rules to instrument flight rules while under the jurisdiction of the Oakland Air Route Traffic Control Center. The aircraft was assigned an altitude of 23,000 feet and proceeded toward Missoula without incident until it was handed off to the Missoula Approach controller.
During the approach phase, the crew was descending through 12,000 feet, approximately 26 miles southeast of Missoula International Airport. It was identified during radio communications that the flight crew lacked the necessary approach charts for the VOR-DME Bravo approach. Although the controller provided the necessary procedural information, the aircraft was operating in an environment with cloud bases at 7,900 feet and other traffic transitioning to visual approaches at 8,000 feet.
As the aircraft began the approach, the crew faced significant challenges, including moderate to severe turbulence and high-altitude physiological stressors resulting from operating an unpressurized, unheated aircraft for over two hours. During the initial stages of the approach, the aircraft deviated from its intended course, turning south away from the airport. Following a descent to 8,600 feet, the Salt Lake City Air Route Traffic Control Center reported that the aircraft had drifted west of the approach course and subsequently vanished from radar surveillance.
After multiple unsuccessful attempts to establish radio contact, authorities notified emergency services and search agencies. Despite an intensive search, no Emergency Locator Transmitter signal was detected, and the wreckage was discovered the following day.
Findings
- The flight crew was operating without the required approach plates for the active VOR-DME Bravo procedure.
- The aircraft was subjected to severe turbulence and high-altitude environmental conditions in an unpressurized cabin.
- The aircraft deviated from the prescribed approach course and disappeared from radar tracking.