That's not surprising:
If it IS correct at 20% (I don't have any insider info) and let's just say there's 6% raises on Date of Signing and 3.5% a year for 4 more years, total 5 year agreement, 20% total, I'd say that's not exactly stellar, not even COLA from when the CBA was amendable. I wouldn't vote for that at AAI.
You need 3% for every year you didn't get a contract raise while you were negotiating and 3% COLA on top of that every year after D.O.S. or you're losing money every year you stay at the same wage, especially the topped-out guys at year 10 or 12 or wherever your scale caps at.
Better be great work rule improvements and/or retirement to boost that number. 10 years without COLA adjustments to wages? That's 36% or thereabouts (when compounded yearly) just to account for inflation!