Tom Cruise continues to defy expectations with his daredevil stunts.

During a Masterclass event at Cannes Fest on Wednesday, writer-director McQuarrie was joined in conversation by Cruise, who made surprise appearance ahead of Wednesday night’s festival premiere of Mission Impossible – The Final Reckoning.

During the panel, McQuarrie revealed some terrifying details from the film.

“When you watch Tom tonight, there’s a moment where he’s in an airplane,” McQuarrie said. “He’s in a biplane, completely alone at the controls, and his biplane suffers some damage. Spoiler, there’s tension in this scene.”

McQuarrie’s only way of communicating with Cruise was via radio, but then, Cruise ventured out onto the wing — something the professional wing-walker they had consulted had warned Cruise not to attempt.

Upon hearing that advice, McQuarrie said Cruise responded, ‘Thank you for your time,’ and it was clear that he would be able to do the stunt.

While Cruise walked the wing, the communication was reduced to hand signals. “He has no radio, which means I have to fly up next to Tom in my helicopter,” McQuarrie said. Unfortunately for McQuarrie, however, the only way Cruise could see him was if he opened the helicopter door and stepped out onto the ledge below. And the strain of being out in the air in those conditions is immense.

“When you leave the cockpit of the plane, it’s like stepping onto the surface of another planet,” McQuarrie said. “The wind is hitting you in excess of 140 miles an hour coming off of the propeller. The molecules in the air are so dispersed. You’re breathing, but only physically. You’re not actually getting oxygen. And [1st assistant director] Mary Boulder is sitting next to me, and she’s got a stopwatch. And when Tom climbs out of the cockpit, I’ll say, ‘Start the clock.’”

They learned that there was a limited window a human could safely be up there.

“In about 12 minutes the fatigue of being blasted by this wind is breaking his entire body down to the point where it’s literally like two hours in the gym,” McQuarrie continued. “And Tom, being the perfectionist that he is, would get to about 12 minutes, and I would lean out the door at the helicopter, and Tom would go, ‘13 minutes.’ There was a moment when Tom had pushed himself to the point that he was so physically exhausted he couldn’t get back up off the wing. He was laying on the wing of the plane. Arms are hanging over the front of the of the wing. We could not tell if he was conscious or not. And we also knew that unless Tom did this, it was expressly agreed he was not in trouble, and he could, like, [call] ‘Cut.’ [But] you can’t do this when you’re unconscious. So we’re waiting to see if there’s any indication if Tom is OK.”

Even more terrifying was that the plane had only three minutes of fuel left — and Cruise had still not gotten up. They had been compelled to fly light, without full tank, due to the aerobatics required.

“He’s got three minutes to get up, but he’s been on that wing for 20 minutes,” said McQuarrie. “And we watched as Tom pulled himself up and stuck his head in the cockpit so that he could replenish the oxygen in his body and then climb up into the cockpit and bring the plane safely down to land. No one on Earth can do that.”