Seagull, the A310 is indeed replacing many of the 722's on specific routes, but it is not a candidate for repl of the entire 722/721 fleet:
1. There were not that many A310's built. Fedex has already procured most of the used A310's available in the past 5-6 years. There are very few -200's left. Relatively more -300's but then these would be heavier and hence less efficient on US domestic routes. However, the # of A310's potentially available worldwide for Fedex would only repl a fraction of the 722 fleet.
2. There will always be a need in the Fedex fleet for an aircraft w the 35k-50k cargo capacity of the 721/722 fleet. Having the F27 (or its replacement) and then only widebodies (the smallest being the A310) would leave too big a capacity gap in between (at around the 50k capacity). Most likely candidates are the 733/734 or the A320 (assuming a cargo conversion program), less likely would be the MD-80.
I dumped at the gybe mark in strong winds when I looked up at a Porter Q400 on finals. Can't stop spotting.