If you read and understood what I said, it's about the whole operation in general, not just the aeroplane. I too have many hours on 747s. Pax 744s and cargo 74Cs. And from my experience, the cargo aircraft get filled to the brim and are therefore operating at the limits of their performance. They have greater MTOWs and MLWs than pax models - and use them. I know they should be able to stop if the performance says so. But taking into consideration with ageing brakes, tyres, reversers, multiple MEL items and tired crews - the safety margins are reduced considerably.
Taking off from HKG 07R in a 74C at 378 Tonnes, the book V1 was 160, VR 182. At V1, there was only about 4000' of runway left. At V1, what was the chance of stopping before ploughing across the railway, the road and into the water? Not good in my opinion. The Air Atlanta aircraft at Sharjah aborted at V1 (IIRC) and went off the end.
I felt I was rarely faced with that situation in a Pax 744.
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