Re: But how?
"777s were grounded when their fuel gauges errored after the Gimli Glider Air Canada incident"
It was a 767. I don't think they were grounded, since the FQIS (Fuel Quantity Indication System) problem was already known and a manual work-around existed. Checking the fuel level with a dip stick. The whole running out of fuel incident occurred because of mis-calculations on the part of the flight and ground crews and other procedural problems.