Originally Posted by bnrdad
The runway at Addison is 7,200 feet long, which is longer than any of the runways at Chicago Midway or Burbank, both of which have a lot of SW flights.
You likely saw a couple of 737-200's. These have all been recently retired by SW, and some have been sold to other operators. SW doesn't do any work at ADI - these were probably undergoing modifications by their new owner(s).
There are several other 737-200s based at ADS. A cargo operator Ameristar has at least two there most of the time (
www.ameristarjet.com). Surprisingly, the hush-kitted 737s make less noise than most of the early model corporate jets (I live about a dozen blocks south of the airport which is one of the busiest private aircraft fields in the country). I would guess the ex-WN planes are scheduled for cargo conversion as they probably have at least 80,000 cycles on them with little lifetime left on them, were purchased for shockingly low prices and would only be useful for infrequent cargo use.