Columbia Airlines Flight 409 is a Boeing 747-100 undertaking a red-eye journey from Washington Dulles International Airport to Los Angeles International Airport, while businessman Scott Freeman is piloting his private Beechcraft Baron towards a sales meeting in Boise, Idaho. Unfortunately, an occluded front has the entire West Coast of the United States enveloped in fog, forcing both Columbia 409 and Freeman's aircraft to divert to Salt Lake City International Airport.
Upon arrival, Salt Lake air traffic control directs Columbia 409 to land before Freeman's Beechcraft. As the large jet begins its descent, First Officer Urias unbuckles himself to investigate a peculiar vibration. In a shocking turn of events, Freeman suffers a heart attack, causing his Beechcraft to violently collide with Columbia 409 just above the co-pilot seat. The impact not only ejects Urias from the plane but also kills the flight engineer and blinds Captain Stacy from the debris. Despite losing consciousness, Stacy manages to engage the autopilot and altitude hold switch.
In the midst of chaos, First Stewardess Nancy Pryor rushes to the flight deck to assess the dire situation. She contacts the Salt Lake control tower, informing them that the cockpit crew is incapacitated and relaying information about the damage sustained by the aircraft. Meanwhile, Joe Patroni, the Vice President of Operations for Columbia, learns about the emergency and, concerned for his wife and son who are passengers, consults with Captain Al Murdock, Columbia's chief flight instructor and Nancy's boyfriend, who is currently experiencing relationship troubles.
Patroni and Murdock board the airline's executive jet, heading to Salt Lake City. Throughout the flight, they remain in communication with Nancy, who informs them that while the autopilot maintains level flight, it is incapable of executing turns. As the jet approaches the mountain range of Wasatch, Murdock coaches Nancy over the radio on how to execute a manual turn. Unfortunately, radio contact eventually falters, complicating the situation further.
Recognizing the impending danger of navigating the mountains without guidance, an air-to-air rescue operation is initiated, utilizing an HH-53 helicopter operated by the U.S. Air Force Aerospace Rescue and Recovery Service. Before the helicopter reaches them, Nancy realizes that the aircraft is dangerously low and heading straight for the mountains. Recalling Murdock's earlier advice about airspeed drops when the aircraft attempts a climb, she approaches Captain Stacy for assistance. With his guidance, she understands that she must throttle the engines forward to gain the power required to rise above the mountains. After executing this maneuver, the aircraft levels off just as the rescue helicopter arrives, and they prepare to send a replacement pilot to the stricken plane.
However, disaster strikes as the release cord from the harness of the pilot becomes ensnared in the jagged metal surrounding the cockpit hole, causing them to fall away before they can board. This leaves Murdock as the only other individual who knows how to land a 747. He is lowered from the helicopter, securely tethered, and enters the aircraft through the breach in the cockpit. After successfully taking control, Murdock fights to land safely at Salt Lake City International Airport amidst decreasing brake pressure that complicates stopping procedures.
Once the plane comes to a halt, the flight attendants quickly initiate an emergency evacuation of the passengers via the evacuation slides, while Nancy and Murdock seize the opportunity to reconcile amidst the harrowing experience they've just endured.
