| * Click on CENTER for graphical tier information | ||
| ZOB (ZOB 1) | ||
| FIRST TIER | ZAU / ZBW / ZDC / ZID / ZMP / ZNY / (Canadian .. CYYC) | |
| SECOND TIER | ZDV / ZJX / ZKC / ZLC / ZME / ZTL | |
| * Click on CENTER for graphical tier information | ||
| ZOB (ZOB 1) | ||
| FIRST TIER | ZAU / ZBW / ZDC / ZID / ZMP / ZNY / (Canadian .. CYYC) | |
| SECOND TIER | ZDV / ZJX / ZKC / ZLC / ZME / ZTL | |