Lear60Capt, I believe the "USAir's checking in with you..." (or any airline) is not a plural, it's a contraction...."USAir is checking in with you...".
The only problem is they actually say "USAir's 452 checking in..." Otherwise, pluralizing it would be USAir 452's checking in. Delta guys do it sometimes too. It doesn't bother me- I just chalk it up to bizarro world, or multiple personality disorder.
Oh, and if you are a GUY and have a plane with SP on the end of the N-number, and you keep calling it Sugar-Pop.. well, let me give you the link to the GPA.... either that or you are getting way too much in touch with your feminine side.