“This is a skyjacking,” it read in part.

“Notify the FBI. I want $502,000.”

The author of the note, Martin McNally, had boarded American Airlines flight 119 in St Louis, Missouri, carrying a sawed-off rifle that went undetected through airport security.

He waited until the plane was 15 minutes from its destination at Tulsa, Oklahoma before he made his move — pulling out his gun, flagging down a flight attendant, and forcing her to deliver his note to the captain.

The 28-year-old planned to force American Airlines Flight 119 back to St Louis where he could get the cash he demanded — $500,000, plus $2000 in spending money — and make the plane re-route to Canada. At some point along the way, he’d use a parachute to jump out with his loot.

It was a bold get-rich-quick scheme for the penniless young navy vet who hadn’t been on a plane before, much less knew how to use a parachute.

But McNally’s daring 1972 caper — which did not come off as he intended — remains one of the world’s most incredible skyjackings, which he recently told in his own words in a gripping episode of the podcast, Criminal.

A BOLD PLOT

Skyjackings were not uncommon in the United States at the time. According to Criminal, there had been 130 between 1968 and 1972.

One of the most infamous was that of a mysterious skyjacker called DB Cooper. In November 1971, Cooper hijacked a Seattle-bound flight by claiming he had a bomb in his suitcase. He demanded $200,000 and jumped out of the re-routed plane with a parachute, never to seen or heard from again.

McNally, totally skint and keen for quick cash, heard the news report about Cooper on the car radio in Detroit.

“I laughed very loud and told my friend that that’s not a bad way to make some money,” he told Criminal.

McNally decided that was exactly what he’d do. But he had to do his research.

He spent time in a library, learning how parachutes worked and trying to figure out terminal velocity.

He also spent months scouting airports across the US midwest to determine the softest target. He settled on Lambert Airport in St Louis.

While metal detectors were being rolled out in airports to catch would-be skyjackers, they weren’t always used for fear it would inconvenience travellers. This was a long, long time before 9/11.

So on June 23, 1972, when an armed McNally walked into Lambert Airport with a flight ticket bought with forged military papers, he had no problem boarding the plane.

“If there had been metal detectors, I wouldn’t have been on that plane. Period,” he said.

“I had a sawed-off rifle, it looked like a World War 2 gun, a pistol and smoke grenade and (I was) dressed like a businessman: suit and tie, sports coat, sunglasses.

“I sat down and we took off.”

Fifteen minutes from Tulsa, McNally went to a bathroom and pulled from his suitcase a wig, gloves and the rifle. He kicked the safety back on the rifle so there were no accidents.

He emerged from the bathroom, armed, and flagged down a flight attendant.

“She said, ‘don’t hurt anybody’,” McNally said.

“And I said, ‘young lady, I’m not here to hurt anybody. I’m here to give the pilot a message’.”

AN UNEXPECTED SNAG

After reading the note, the pilot came over the intercom to announce a passenger needed to return to St Louis, so the plane was turning around.

Once it landed in St Louis, McNally ordered women and children off, and then decided to also let go anyone who was elderly, had a heart condition, or was on medication.

Unsurprisingly, everyone took the opportunity to get off the plane.

But McNally needed hostages. He made 15 men stay behind, along with the flight crew, and demanded the plane circle over St Louis while banks pulled together his $502,000.

After about five hours, the plane landed at St Louis again and McNally was given his money in a bag. He gave $2000 to flight attendants as a tip.

He also received other items he’d demanded: two shovels, goggles, five parachutes, two harnesses, and an altimeter for measuring altitude.

Finally, at about midnight, McNally kept one passenger hostage on the refuelled plane and it started preparing for takeoff.

But he didn’t expect what would happen next.

A businessman named David Hanley, who was watching coverage of the runway drama from inside a terminal, became suddenly enraged by what he saw.

He left the terminal, got in his Cadillac El Dorado and managed to drive it into the runway, where he sped towards the plane on a collision course. With the plane’s tank freshly filled with jet fuel, the impact could have been disastrous.

The pilot hit the brakes and while the Cadillac struck, there was no explosion.

But it was a major setback for McNally.

“What the pilot did was slam on the brakes, the plane bounced twice, I think at that point everything came to a stop,” he said.

“I realised we were really hit by some damn fool (and) we’re going to have to order another plane.”

With authorities and emergency services surrounding the now-damaged plane, another passenger jet was brought in as close as possible so McNally and his hostages could move from one to the other.

Nervous that FBI sharp shooters would take a potshot while he was making the transfer, he used two flight attendants as human shields.

“I would say I was even scared,” he said.

“I told the pilot to tell the FBI … if I see any lights or any beams this thing could come to a screeching halt very quick with an explosion.

“I said, ‘I don’t want any hanky panky when we make the move from plane to plane’.”

McNally was eager for the second Boeing 737 to take off as soon as possible for Toronto. Mr Hanley’s stunt had put him way behind schedule and he needed to jump out of the plane before sunrise.

THE JUMP

“Never in my life had I put on a parachute,” McNally recalled.

He said four flight attendants watched him as he tried to get his leg straps on. He asked one of them for help.

“And she says, ‘I don’t think we’re supposed to be doing this’. And I said, ‘young lady, trust me: you’re supposed to be doing anything I tell you do to’.”

McNally used twine to tie the bag of money around his leg and used his belt to secure it. His plan was to jump out, land safely, bury the money, lay low for a while and then go back and retrieve it.

But as the plane cruised towards Toronto he had sudden second thoughts.

“I (thought) yeah, this is precarious. I have some options here,” he said.

“I can go up to the cockpit and give them the gun and say this is a joke, or I can kill myself, or I can take a chance on bailing out.

“I decided well, I better bail out. And if I make it, fine, and if I don’t, death comes quick.”

McNally jumped. His goggles instantly came off. When he pulled the cord of the parachute, the violent jolt caused his money bag to tear off his leg and fly off.

The money — the whole point of the hijacking — was gone.

McNally had barely landed on a field in Indiana with an almighty thud to his head when he was already making plans to try it all over again a couple of weeks later.

But that wouldn’t be.

The FBI were searching desperately for him. The next night, McNally ditched his gun and hitchhiked to Detroit — and incredibly, the local police chief picked him up, not knowing who he was.

“He said, ‘it’s not safe to be on the streets tonight, there’s a lot of excitement,’ and I said, ‘yeah, I heard about the search that’s going on here for that skyjacker’,” McNally said.

“He said, ‘yeah, there’s a lot of FBI around here’. I said, ‘I can imagine.”

It wasn’t long before a farmer found McNally’s ransom money and another farmer found his gun. It would take federal police six days to find McNally, and they nabbed him as he was walking home.

They had his fingerprints on the plane and the note. McNally was charged with two counts of federal aircraft piracy and found guilty in court. He was sentenced to life in prison.

McNally reckoned the cost of planning the failed skyjacking was more than $2000 — driving from airport to airport, buying the gun, sourcing his equipment.

Hearing his verdict, McNally recalled thinking: “I got life and it cost me two grand.”

But the sour ending wouldn’t deter McNally for long.

In a supermax prison in Kansas, serving his life sentence — which was 30 years at the time — McNally was approached by another convicted skyjacker, with whom he hatched an escape plan using a helicopter hijacked by an accomplice on the outside.

He was up to his old tricks. That plot failed, too.

McNally eventually left prison early the old fashioned way, with good behaviour.

And even though he could if he wanted, he’s never stepped foot on another plane.

- Do you have a horror flight story to share? Continue the conversation with Lauren McMah on Twitter @lauren_mcmah