Of the 396 passengers and crew aboard the Pan Am plane, 275 had boarded in Los Angeles. On their way to a Canary Islands cruise ship, the LA passengers were flown to New York City where more passengers and a new crew boarded the jumbo jet. By the time their plane was blocked by KLM’s 747, the LA passengers had been traveling about 13 hours.
Captain Victor Grubbs was in command of Clipper 1736 (the plane’s call sign). He was assisted by First Officer Robert Bragg and Flight Engineer George Warns. Wanting to leave
Tenerife, Bragg and Warns measured the distance behind the refueling KLM plane. They confirmed what Captain Grubbs believed: There was not enough maneuvering room for Clipper 1736.
When Las Palmas radioed Tenerife that a gate was finally available for the KLM plane, Captain van Zanten was given permission to start his engines. The big jet was now fully loaded with enough fuel to fly to Amsterdam, after it dropped off and picked up passengers at Las Palmas. It was cleared to commence a "back taxi" down the active runway where it would do a 180-degree turn at the end, to position for take-off.
The Pan Am flight was also given clearance to start engines. Captain Grubbs wanted to hold until after the KLM jet had taken off, but ground control instructed the Pan Am crew to ALSO commence a back taxi down the active runway. Clipper 1736 was instructed to turn off the active runway on exit C3. That turn would have put the Pan Am 747 on the taxiway where it would hold for its turn to take off. But the Pan Am crew missed the exit.
As the Pan Am plane continued toward exit C-4, the KLM jet had ALREADY made its 180-degree turn at the end of the runway. Both planes were now facing each other. Due to bad weather, neither crew could see the other plane. At least, not yet.