You guys are talking past each other. Southwest has four lines of heavy overhaul, as provided under your contract. There were three, and once the fleet hit 621, your scope clause required a fourth.
700 misspoke when he said "C checks" as those are not necessarily heavy maintenance. Under your contract, all C checks are in-house. Obviously, WN calls heavy overhaul something else - at AA they were (still?) called "Heavy C checks." According to AA, a narrowbody C check is performed about every 15-18 months, takes about three days and about 2,100 man-hours.
Every few years, a heavy C check is performed, which takes 3-5 weeks and requires 20,000 to 30,000 man-hours. Except for the four lines at DAL, all WN heavy airframe overhauls are performed by contractors. WN says so in its 10-K, where it tells investors that WN performs "substantially all" of its line maintenance in-house, but contracts with outsiders for most of its heavy overhauls, and they consume the majority of WN's maintenance expenses.
Correct. But those C checks don't take much time or money. Your contract guarantees that all of them will be performed in-house. They certainly don't require very many mechanics, as the roster of AMTs does not appear to be growing very fast at WN. Just 2,300 AMTs, plus 300 stock clerks and 200 appearance techs (cleaners). That's a lean workforce for more than 700 aircraft.