F-106A 57-2453 in Dec 1960 with 498th FIS, Geiger Field, WA. They were testing fuel shifting at McClellan AFB CA and got too much weight aft. A GD/Convair field team was installing qualified cold-weather fuel valves. This happened during the refueling check-out phase when someone forgot to manually turn off a valve in the main wheel well on this early configured aircraft. The result was that the fuel wasn't distributed properly and it caused a center of gravity situation where there was more weight behind the main landing gear than there was weight forward of the main landing gear. [via Joe Sylvia]