LY744 From Canada, joined Feb 2001, 5536 posts, RR: 10 Reply 5, posted (10 years 11 months 1 week 4 days 17 hours ago) and read 1022 times:
The first A319s delivered were powered by the 5B (A319-111, A319-112), and the 5As appeared later on. Therefore, the chronological system remained in place. The conclusion is that the 5A4 and 5A5 CFM-56's that are used on the A319 are less powerful, but they are actually newer than the 5B5's and 5B6's. The 5A1 is the original version for the A320 family dating back to the late 80's. For whatever reason Airbus/CFM added the 5A's to the A319 as an option, perhaps due to airlines seeking extra commonality with their older A320's, or perhaps due to acquisition/operation costs.