I think this might be the worst part. Straight from LOA 3 4.e.iii
"US Airways may make the determination, in its sole discretion, that there is an insufficient number of qualified PSA pilot candidates in any given month in which US Airways hires pilots for New Pilot Positions. If that determination is made in any one or more months, US Airways’ Offer Commitment in the relevant calendar year shall be reduced by the number of positions that otherwise would have been offered to a PSA pilot had there been sufficient qualified PSA pilot candidates." Its a loophole to get around one of the biggest parts of the agreement while still freezing pay.