In early 2012, James Cameron was bolted into the cramped pilot’s chamber of a torpedo-shaped submersible he had designed and hoped to ride in, alone, to the deepest point in the world’s oceans, a place no human had traveled to in 50 years. For the director of “Avatar,” it was his most technologically audacious project yet.

But as he sank to the bottom of the western Pacific on a test dive, Cameron’s life support system came loose from its mount and landed in his lap. On another test, his communication system failed — his ability to signal his crew above the sea lost. Cameron said he coped with the danger by running through checklists of safety procedures in his head.

“It’s very calming, very ritualistic,” Cameron said recently in an interview at his Malibu compound. “You try A, you try B, you try C, and hopefully you don’t ever get down to F, cause we all know what that stands for.”

It was a moment that summed up Cameron’s approach to filmmaking — and life itself. He’s daring but detailed, an adventurer who prides himself on being prepared and someone who always fiercely follows his own path up or down.

In March of that year, Cameron realized his dream, touching the sea floor in the Mariana Trench, a forbidding valley more than 36,000 feet down in the Pacific near Guam that has been reached only once before, by U.S. Navy Lt. Don Walsh and Swiss oceanographer Jacques Piccard in 1960. The new film “Deepsea Challenge 3D” documents the director’s often-harrowing journey to make the deepest solo dive in history, an expedition that included several false starts, rough seas and the tragic loss of two crew members in a helicopter accident.

Produced by National Geographic and directed by John Bruno, Ray Quint and Andrew Wight, “Deepsea Challenge 3D” also sheds some light on Cameron’s unconventional pastime. Though he has directed the two highest-grossing movies of all time (“Avatar” and “Titanic”) and is currently at work on three anticipated “Avatar” sequels, Cameron has said he finds his deepest pleasures far away from film sets, under the sea.

“I like exploration, and I have since I was a kid,” Cameron said. “For me the big heroes were never sports heroes. They weren’t music gods. They were explorers. I was much more interested in Buzz Aldrin than John Lennon.”

A tinkerer and adrenaline seeker, Cameron is in the unusual position of being able to finance his fantasies thanks to his outsize Hollywood successes — and his extracurricular hobby of deep-sea diving has always influenced his day job. He pitched the movie “Titanic,” which would go on to win 11 Oscars, in large part so that 20th Century Fox would finance a dive to the wreck of the British passenger liner, and he drew inspiration for the bioluminescent life in “Avatar” and the underwater traumas of “The Abyss” from dives he took.

“Working with Jim, it’s always an adventure,” said Bruno, a visual effects supervisor who has been part of Cameron’s professional circle since the 1989 underwater adventure film “The Abyss.” “Something’s coming our way that’s gonna be cool, and I know he can get it done. With other directors you wonder, if we start this, will it finish? I never worry about that with Jim.”