According to a short article I just read on this re-engining program Boeing chooses to call the "max", it's simply an updated CFM-56 with a slightly larger diameter fan. They claim it will be 4% more fuel efficient than the re-engined A-320. Maybe a big deal if you're an airline stock analyst.
Among the issues to be resolved is how big they can make the fan without it requiring "major" re-design of the aircraft related to engine pod ground clearance issues. I surmise that they could mean landing gear, engine/wing interface and gear well changes when they refer to re-design.
The article also mentioned the long lead time involved but did not go into detail about the logic driving the proposed schedule. As far behind schedule as Boeing is on their current offerings, it' not surprising though.
Last edited by westhawk; 31st Aug 2011 at 08:35.