Appeal on a check swing

[bob jenkins]

Originally posted by SC Ump
With three umpires and bases load, U1 is in "B" and U3 is in "D". With a right handed batter and a check swing appeal, who does the PU go to?

I cannot remember specifically, but believe in the past I have seen double-A minor league PUs go to U1. This year they have been going to U3, i.e. the "opposite" umpire rather than the one in the middle. Is that the norm?

Some leagues always go to the umpire on the line in this situation. (If both are on the line, go to the "open" umpire, of course.)