John Travolta watched in shock as a hair-raising movie stunt HE was scheduled to perform next went horribly wrong — injuring TWO people — and screamed, “OH, F—! WE’RE NOT DOING THIS!” In the star’s new flick “Swordfish,” a helicopter suddenly yanks a bus full of hostages high in the air — a dangerous scene to film. Travolta told my spy: “They hung the bus upside down in the studio — and we were on thin little cables” designed to secure each actor. Despite assurances the cables would hold 2,200 pounds, 200-lb. Travolta was skeptical. Producers ordered a stuntman to try it first and . . . DISASTER!! His cable snapped and he plummeted — crashing down through the windshield and hurting another actor! Travolta yelled, “GET THAT BUS DOWN . . . GET THOSE CABLES OFF! WE’RE NOT DOING IT!” Explained the star: “What they forgot was . . . 200 pounds can very quickly turn into 2,000 when you put force on it. There’s some arithmetic I think was forgotten!” Producers went back to the drawing board, rejigged the stunt — and did it safely!