I think the aircraft used for ETOPS go in for "extended" maintenance every winter - I need to stop using the term "heavy" maintenance since that's a term used for a major maintenance check every 5-6 years. Short of finding something that needs longer to fix, most won't be in maintenance over a few weeks. Of course, as the interval for heavy checks implies, a couple of the A330's and 767's will be in for their heavy checks each winter plus 3-4 757's.

There is an alternative that US may have gone to. The FAA will approves progressive checks. Using 5 years for the normal interval on heavy checks, a carrier can get approval to do 20% of a heavy check every year so after 5 years a complete heavy check is accomplished. Most planes would be out of service longer but none would be out of service as long as doing a complete heavy check would take.

Since US has spare ETOPS planes in the winter due to the seasonal service to some destinations, either way would work.

Jim