I saw the performance mentioned in Chris's note above in action one very hot mid-day in Nairobi. I was on the "waving base" at Embakasi waiting for an incoming visitor, when an Ethiopian Boeing 720 trundled off to tuck it's tail, so to speak, in to the hedge to use all of the runway. Amid much black smoke it rotated and looked as though it might have difficulty clearing Ol Donyo Sabuk, an extinct volcano some miles from the airport. By contrast an East African Super VC10 taxiied out just after it and promptly took off from the intersection which was about halfway down the runway, to the mighty roar of 4 Conways at full chat. I don't know whether it was an airtest or a scheduled flight but it was very impressive...