@ CliveL
Thanks for that detailed and very interesting description of the fuel handling on Concorde and I agree that 17% ullage does seem to be very high, I've never come across a figure that high, ever. But your paragraph 5 seems to indicate that it was a jolly good idea from a flight safety point of view. The risk of tank rupture was increased because of the limited free surface volume. I'm just interested in what the circumstances were that allowed this restriction to be over-ridden.