The Structure

The Sections of the Sky

You are probably familiar with Victor airways from reviewing sectional charts as a private pilot.  In the IFR world, we almost always try to fly along “airways” and not always Victor’s airways.

Airways in the sky have a distinct advantage over just flying direct somewhere. You can generally get right to an IAF from an airway and you also are able to fly lower on a safe and proven route rather than blazing your own path up high.  (Why do you want to fly lower? Icing for one big reason, among others!)

There are two main types of airways in the sky.  Those defined by VORs and those defined by GPS.  They are then further divided into low and high airways and on the corresponding charts (low or high enroute charts).

gps and low enroute charts

Low Enroute Charts

The low enroute chart above shows both Victor airways and “T” routes.  A “T” route is just a GPS airway.  All the same rules apply to all airways:

  • They are controlled airspace
  • They are 4nm wide each side of the centerline
  • Victor airways and Jet airways get wider than 4nm either side of the centerline as you get farther from the VOR station
  • Airways with a changeover point more than 51nm from the VOR, at 51nm from the station and further the width of the airway increases to 4.5 degrees wide (thus getting wider and protecting you from terrain the farther you get from the station with a not so accurate VOR receiver)
  • Victor and “T” airways go from 1,200′ agl to 18,000′ msl unless otherwise specified. (They are class E airspace unless otherwise specified).

Why are airways so wide?  Well to protect you from terrain when you might get a little off course. Not that you’re going to try and be off course, but remember your VOR can legally be 4 degrees off from reality, thus even when you are holding the course perfectly on the CDI, you may be off course.  Also, note the ground track below, Pilots don’t always fly so straight when the autopilot is off.

radar flight track

High Altitude Enroute Charts

high altitude ifr routes

Good news, your little airplane probably won’t make it up to an altitude where you could ever actually use this chart!  High charts are for FL180-FL600.  There’s a lot less detail on the chart, since there’s a lot less “stuff” going on from 18,000′ up into the stratosphere.  Being that there is a lot less information on these charts, the scale is also less where you’ll have a larger geographic area on one chart.  The idea with these charts is that you are going to be covering a very large distance very quickly (like in a jet).  You’ll find “jet routes” and “Q routes” on these charts, the high altitude counterparts of Victor Airways and “T” airways.