The de-rated heavy weight average time from TOGA to liftoff is just over 50 seconds. Considering liftoff speed at heavy weights is about 175 knots, then that's a distance of about 2500 metres give or take.
It sounds like you want to know the minimum unstick speed carl. In testing they whack an almightly piece of wood on the tail and drag it along the runway until the thing lifts off. It's the minimum fly speed, and you really don't want to see it. At a rough guess it's about 140-50 knots at heavy weights.
There have been a number of incidents where some twit (as you put it 18 wheeler!), has taxied in front of an aircraft taking off. One particular case I have heard about was after V1 but before VR. The aircraft was snatched, scraping both the tail, and engine #1. Both aircraft involved were 747s.
There was an incident at sydney were a 747 was towed across the runway in front of another 747 taking off. The aircraft was able to rotate normally and managed to clear the taxiing plane. Had it been a heavier wieght though!
I guess you could go for the parallel taxiway...
SS
Last edited by Silver Shadow; 15th Oct 2002 at 03:23.