| * Click on CENTER for graphical tier information | ||
| ZAB (ZAB 1) | ||
| FIRST TIER | ZDV / ZFW / ZHU / ZKC / ZLA | |
| SECOND TIER | ZAU / ZID / ZJX / ZLC / ZME / ZMP / ZOA / ZTL | |
| * Click on CENTER for graphical tier information | ||
| ZAB (ZAB 1) | ||
| FIRST TIER | ZDV / ZFW / ZHU / ZKC / ZLA | |
| SECOND TIER | ZAU / ZID / ZJX / ZLC / ZME / ZMP / ZOA / ZTL | |