Ed Sett,
"A restrictor is now fitted into the refuel pipe for No 5 tank,"
Just a thought Ed, with the 5 tank under a normal refuel pressure of 50 psi, what would be the back pressure behind this restrictor acting on the 5 tank refuel line along the Stbd rib 1? As you know the 5 tank is always the last to fill when uplifting a large fuel load and to my mind, when the second to last tank is shut off, would there not be a pressure increase or 'pressure spike' down the 5 tank refuel line as a result?
DS