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When word came that the Las Palmas Airport had been reopened, the KLM craft was still refueling, blocking the Clipper's way. Pan Am First Officer Robert Bragg radioed to KLM, asking how much longer the refueling would take. "About 35 minutes," came the crisp reply. Bragg and Grubbs measured the clearance around the KLM plane, found it inadequate to taxi past. KLM would have to take off first.
Visibility was later officially described as "500 meters [about a quarter-mile] and changing" when Captain Grubbs finally told the passengers: "We are taking off now." This meant that most of the 11,155-ft. runway (nearly two miles) was invisible to a pilot at one end of it. It also was hidden from the view of the tower controllers, who as at many similar airports, had no ground radar to help them track surface traffic. For unexplained reasons, the white centerline lights embedded in the runway—a further aid to pilots when visibility is poor—were not operating. Inside the Clipper, Edward Hess, 39, a food broker from Phoenix, thought, "I don't know much about this, but this is below minimum." In fact, the degree of visibility remained an important point for investigators.
Though key questions remain, investigators have little doubt about the general sequence of events that followed. The tower ordered KLM to taxi the full length of the runway, make a 180° turn and hold. It ordered Pan Am to follow about three minutes behind and turn off at the "third intersection." There were four such turns (see diagram) providing runway access from the terminal apron and taxi strip. Ten planes congesting the apron blocked the jumbos from using the full taxiway to reach their takeoff point. KLM confirmed its orders and proceeded. Pan Am followed at about 6 m.p.h. In good weather, 20 m.p.h. would be normal. As the two planes moved up the runway, KLM asked the tower to confirm that Pan Am would move off at the third exit ramp. The tower reply: "Affirmative. One, two, three. The third one, sir."
The KLM crew asked for air-control clearance—meaning its flight path, not approval to take off. The tower provided the instructions. As required, KLM repeated the directions to confirm it had heard correctly.
"We are now on [or at] takeoff," said KLM.
"Stand by for takeoff clearance. I will call you back," replied the tower.
Since both pilots and the tower were tuned to the same radio frequency, the Pan Am crew heard this exchange. "He's not cleared for takeoff," someone in the Pan Am cockpit concluded reassuringly.
"Clipper 1736, report clear of runway," said the tower.
"We'll report when clear of runway," Pan Am replied.
"Roger, thank you," said the tower.