This article originally appeared in IFR magazine, Jul. 2005.It was late in 1981 or maybe early in 1982, because that's the only time in the history of O'Hare that the draconian departure restrictions in this tale were used. To understand how those departure restrictions fit into our story, you need to know a little about how IFR departures work at the world's busiest airport. Everybody gets the same instrument departure procedure (currently the O'Hare One), which routes them over one of more than a dozen standard departure fixes, depending on requested altitude and direction of flight. If you're eastbound at high altitude, you can file whatever you want but you'll get the O'Hare One over either Keeler (ELX) or Gipper (GIJ). These fixes coincide with a letter of agreement between Chicago TRACON and Chicago Center, specifying that the TRACON ensures all high-altitude, eastbound departures are handed off to Center in two single-file lines, one destined to pass over each fix. Similar agreements cover high-altitude routes in other directions. The radar separation minimum for most Center operations is five miles, but in order to allow for margin of error (and these days, to keep the computer "snitch" quiet), the actual in-trail spacing on these routes is closer to seven.
After a decade of outsourcing, the tide is now flowing in the opposite direction. More