Planes Face Each Other on the Active Runway

The Pan Am pilots know that both 747s are on the same active runway.  KLM will takeoff first. 

Visibility is still poor.  The Pan Am crew cannot see the KLM plane, which means the KLM crew cannot see the Pan Am plane.

FERNANDO AZCUNAGA [Tenerife ground control]: "Pan Am 1736, report runway clear."

ROBERT BRAGG [Pan Am First Officer]: "Okay, we'll report runway clear."

FERNANDO AZCUNAGA: "Thank you, 1736."

Robert Bragg tells us what happened next in the NOVA documentary, The Deadliest Plane Crash. 

"He asked us were we off the runway, and I responded back negative, we are still on the runway but we will report clear of the runway. That was the last thing I said, over the radio.

"We were only taxiing at three miles an hour. Nothing in my mind would have even given me the thought that he was taking off."

Credits

Dialogue between ground control and Pan Am 1736 from the official Spanish investigation (modified for ease-of-use here).

Robert Bragg quote from the transcript of NOVA's documentary, The Deadliest Plane Crash.

The above image is from a Russian-language web site on the Tenerife disaster.