While First Officer Meurs repeated the ATC instructions, van Zanten released the brakes at 17.06:11. One second later, he said
Let’s go, check thrust.
The First Officer continued to read back the ATC clearance to the tower. He finished his communication with these words:
We are now at take-off.
Listening in, the Pan Am pilots became concerned. Didn’t the KLM crew know both planes were now
facing each other (don't miss this video) on the mist-shrouded runway?!
After the KLM first officer repeated the ATC clearance, and at the precise moment the tower replied by telling the KLM crew,
...stand-by for take-off, I will call you,
Clipper 1736 advised the tower:
...we are still taxiing down the runway, the Clipper 1736.
KLM 4508 heard neither ground control nor Pan Am’s first officer. (Follow the link to 1706:19.39) The simultaneous transmissions sounded like a three-second squelch to the KLM crew.
Another exchange between the tower and Pan Am 1736 was heard by KLM’s flight engineer:
Tower: Roger, papa alpha 1736, report the runway clear.
Pan Am 1736: OK, we’ll report when we’re clear.
At 1706:34.7, KLM’s Flight Engineer William Schreuder became
alarmed (scroll to the end and look for the transmission at 1706:34.7):
Is he not clear, that Pan American?
Both the captain and first officer replied simultaneously:
Yes.
They were wrong. KLM 4805 continued to roll down the runway on a collision course with Pan Am 1736.