A report filed with NASA’s Aviation Safety Reporting System and published in June outlines how a passenger aircraft flew off course during a period of GPS jamming and nearly crashed into a mountain. Fortunately, an alert radar controller intervened, and the accident was averted.

Friedman Memorial Airport serves the ski resort town of Sun Valley, Idaho. Mountain peaks in the area are in excess of 12,000 feet. Airport arrival and departure procedures are carefully structured to ensure aircraft maintain safe distances from terrain.

According to the report, when “Aircraft X” arrived there was “…an abundance of smoke in the area” of the safe arrival route. Also “During this time there was widespread GPS jamming… Almost every aircraft was reporting…GPS outages.” Two previous flights had advised that their GPS signals were interrupted, but came back on line in time to make a safe approach to landing.

Aircraft X also reported problems with GPS, and then advised air traffic control that GPS had come back on line and was working well. The controller then cleared the aircraft for a GPS-based approach, including descending to 9,000 feet. Communications with and control of the aircraft was switched from Salt Lake Center (250+ miles away) to the tower at the local airport.

Shortly thereafter, the controller in Salt Lake City noticed Aircraft X straying off course. Also, it was at 10,700 feet altitude and nearing a 10,900 feet mountain. He quickly contacted the local control tower and the aircraft was directed back onto a safe flight path.

The report concludes that “Had [the Radar Controller] not noticed, that flight crew and the passengers would be dead, I have no doubt.”

Dana A. Goward is president of the Resilient Navigation and Timing Foundation.