It was on the wintry afternoons of 24 November 1971, when a middle-aged man, about 6 feet (1.83 m) tall, carrying a black briefcase, approached the busy flight counter of Northwest Orient Airlines at Portland International Airport. He identified himself as Dan Cooper and paid US$ 20 in cash to purchase a one-way ticket on Flight #305, a 30-minute trip to Seattle. Dan Cooper, dressed in a dark suit, black tie with a mother-of-pearl tie-clip, and neatly-pressed white collared shirt, boarded the aircraft, a Boeing 727-100, took seat 18C (15D or 18E by other versions), lit a cigarette, and politely ordered a drink, bourbon and soda.

Shortly after takeoff from Portland as scheduled at 2.50 pm Pacific Time, Cooper handed a note to Florence Schaffner, the flight attendant nearest to him in a jump seat attached to the aft stair door. However, assuming the note contained a lonely businessman’s phone number for obvious reasons, she decided to ignore it and dropped it in her purse without having a glance. At that point, Cooper leaned towards her and firmly whispered to immediately have a look at that note as he has a bomb with him.

Florence Schaffner could not exactly recollect the wordings of the note as it was later reclaimed by Cooper, but she reported that it was a neat note with all-capital letters with a felt-tip pen that instructed her to sit next to him to have a look at the bomb. It made the stewardess stunned and as she sat next to him as instructed, Cooper opened his briefcase long enough for her to glimpse eight cylinders, four on top of four, attached to wires coated with red insulations, along with a large cylindrical battery. After that, Cooper asked her to take down a note about his demands comprising of US$ 200,000 in $20 bills; four parachutes, two primary and two reserves; and a fuel truck in Seattle airport for refueling the aircraft. Florence Schaffner went to the cockpit to hand over the note to the pilot and when she returned, she found Cooper wearing dark glasses.

As the pilot of the plane, Captain William A. Scott, immediately contacted Seattle-Tacoma Airport traffic control to inform them about the uncalled for situation in his aircraft, they in their turn informed the matter to the local and federal authorities. Soon, the pilot was instructed to circle around the Puget Sound area for approximately two hours to give time to the Seattle police department and the FBI to arrange for Cooper's parachutes and ransom money as well as to mobilize emergency personnel.

At the same time, the pilot was also instructed to inform the 35 passengers that their arrival in Seattle would be delayed due to a minor mechanical problem, assuring safety.

FBI agents made no delay and made the best use of those two hours. They assembled the ransom money, 10,000 unmarked 20-dollars bills from several Seattle-area banks and made a microfilm photograph of each of them. As Cooper rejected the military-issue parachutes offered by McChord AFB personnel and demanded civilian parachutes with manually operated ripcords, Seattle police also obtained them from a local skydiving school. However, throughout those long two hours, Cooper remained cool and calm, polite and soft spoken, not at all consistent with the stereotype of enraged hijackers. He was not nervous and seemed rather nice. According to flight attendant Tina Mucklow, Cooper appeared familiar with the local terrain and at one point rightly identified Tacoma below.

The aircraft landed at Seattle-Tacoma Airport at 5.30 pm, more than an hour after sunset and as instructed by Cooper, Captain Scott took the jet to an isolated, but brightly lit section of the tarmac and closed all the window shades in the cabin to dissuade police snipers.

By that time, Al Lee, the operation manager of Northwest Orient in Seattle, had approached the aircraft in plain dress, due to the apprehension that Cooper may mistake his airline uniform for that of a police officer, and take unwanted offensive action. To avoid any such complication, he approached the plane as a civilian and completed his job by delivering the cash-filled knapsack and parachutes to flight attendant Tina Mucklow, via the aft stairs. As his demand was fulfilled, Cooper released all the passengers, along with Florence Schaffner and other staff members, except two pilots, a flight engineer and a flight attendant.

After refueling, Cooper instructed the pilot to fly to Mexico, at the minimum airspeed, approximately 100 knots (115 mph) and a maximum 10,000 feet (3000 m) altitude.  Ridiculously, despite the vehement objection of the Northwest’s home office, he also directed that the aircraft should take off with the rear exit door open and its staircase extended. As the Boeing 727 took off at about 7.40 pm, Cooper asked flight attendant Tina Mucklow to join the rest of the crew in the cockpit and remain there with the door closed. However, two fighter aircraft followed the Boeing, one from above and one from below, which Cooper did not know. But something was wrong from the beginning of the journey and approximately at 8 pm, a flashing warning signal in the cockpit indicated that the aft airstair apparatus had been activated. As if that was not enough, it was followed by a subjective change of air pressure, which indicated that the aft door was open. Nevertheless, when the Boeing 727 landed at Reno Airport in Nevada at around 10.15 pm, it was found that Cooper was not in the aircraft. Cooper was never found again, he had just disappeared mysteriously into the night, and his ultimate fate remains a mystery to this day.

It was presumed that a little after 8.30 pm, somewhere between Seattle and Reno, widely believed to be near Ariel in Washington, Cooper lowered the rear steps and jumped out from the plane in the darkness of the night with a parachute and the ransom money, never to be found again. Neither of the two following fighter pilots saw anything exit the airliner, visually or on the radar. Even, none of them saw an open parachute in the sky. However, it is also true that, with extremely limited visibility at night and cloud cover obscuring any ground lighting, there is every possibility to miss an airborne black-clad human figure in the night sky. The FBI agents recovered Cooper's black clip-on tie, his tie clip and two of the four parachutes, one of which had been opened and two shroud lines cut from the canopy. Several circumstantial pieces of evidence suggest that Cooper did not survive his jump from the plane. Firstly, he was dressed in a business suit, trench coat and loafer shoes, which were unsuitable for a rough landing. Apart from that, at the altitude of around 10,000 feet, in which the airliner was flying, the wind speed was likely to be more than 322 km (200 miles), and the parachute he used could not be steered. Even, he did not notice that his reserve parachute was sewn shut for use in training. Moreover, he had jumped in a rugged, heavily wooded area at night, which is a dangerous proposition for even a seasoned pro and the available shreds of evidence suggest that Cooper was not a seasoned diver.

The FBI coordinated an aerial search, using both aircraft and helicopters, all along the entire flight path of the Boeing 727, when numerous broken treetops and several pieces of plastic and other objects resembling residuals of a decaying parachute canopies were sighted and investigated, but nothing relevant to the hijacking was found. The investigators got a break in 1980, when a young boy on vacation with his family found three decaying packets containing US$ 5.800 that matched the ransom money serial numbers. The packets were buried along the River Columbia, about 32 km (20 miles) from Ariel. However, why one of the packets contained only $800, instead of $1000, remained unexplained. Unfortunately, despite an intense search around the area, nothing further was discovered and the mystery of Don Cooper remained a mystery forever.