You aren’t supposed to fly a Boeing 747 with its throttles.

That’s the first thing to know about the final, terrifying 32 minutes of Japan Airlines Flight 123. The throttles can make a plane climb, descend, accelerate, or slow. If you’re truly desperate, they can even create a crude turning force if one side of the plane generates more power than the other. But the throttles aren’t a rudder.

On August 12, 1985, after taking off from Tokyo’s Haneda Airport, JAL 123 was supposed to make a routine 54-minute flight to Osaka. A dozen minutes later, at roughly 24,000 feet, the aft pressure bulkhead ruptured.

The blast tore away the tail cone, the auxiliary power unit, and a major portion of the vertical stabilizer, including the rudder. Most critically, it severed all four hydraulic systems that powered the 747’s control surfaces.

“All four” means a mechanical nightmare. The airplane’s hydraulic systems do the heavy lifting, not the pilot. They translate the cockpit commands into movement at the rudder, ailerons, elevators, and other surfaces.

When those systems were lost, the JAL 123 crew still had a massive 747 beneath them. But not one that would respond in any normal way.

NASA would later study this kind of disaster scenario under the name “propulsion-controlled aircraft.” The basic idea is you add thrust to climb, reduce thrust to descend, and split thrust between engines to help turn. But NASA’s work also showed why this isn’t a great substitute for real flight control. Yes, you can sometimes keep an airplane flying with manual throttle-only control—but it’s slow, not very precise, and vulnerable to oscillations.

Instead of having a computerized system to smooth out those corrections, JAL 123 only had Captain Masami Takahama, his crew, and four engines. The 747 pitched up and down in a phugoid cycle while rocking side to side in a Dutch roll. Survivor Yumi Ochiai later compared the sensation to a falling leaf.

The crew tried anything they could, adjusting power, attempting to turn back toward Haneda, and using what remained. When Tokyo air traffic control asked, “Can you control now?” the answer from the cockpit was simple and haunting: “Uncontrollable.”

The airplane had lost the hidden systems that made normal flying possible. The fact that the crew kept flying for an astonishing 32 minutes showed how much they were able to do with almost nothing left.

The terror of those final minutes only scratches the surface of the real mystery: Just how did one of aviation’s most famous airplanes ever get to that moment in the first place?

For the stunning answer, that story begins years earlier, with a repair hidden in the tail of the “Queen of the Skies”. Read Pop Mech’s entire explosive feature, “How a Faulty Repair Led to the Deadliest Single-Airplane Crash of All Time” now.