OK Fobotcso, I was only a stude so we didn't need to know how the jet worked. Now you remind me, pressurised to 250. Remember a civilian quack gave me a glass bottle and pipette as nasal drops. Real handy in a screaming J*s*s for base.
I a Vulcan, 450 over London, the senior officer in the right hand seat responding to the check "Fuel Tank Pressurisation" responded "No Pressure". As one, the rear crew clamped their mask toggles down and the co, in the LHS, initiated a max rate descent below 390.