In the last flight, we used two forms of VFR navigation to get from Bozeman to Jackson Hole: pilotage and dead reckoning. Now that we are IFR, we need a form of navigation that also works if we are in the clouds and unable to see the ground. Airways are IFR routes established to provide safe passage over obstacles, and exist all across the country. Historically, these airways only connected ground-based navigation aids like VORs. More and more, airways are now being established between GPS-based points. It’s also more possible than ever to fly "directly" between two points or even straight to your arrival airport.
The advantage to using airways is that obstacle clearance is built in. For example, if you decided to fly directly to KSLC from KJAC, you would be flying over peaks higher than 13,000 ft. with no reliable way of knowing how to avoid them. Airways provide safe passage over terrain by establishing a Minimum Enroute Altitude (MEA) that, if flown, guarantees obstacle clearance, as well as radio and navigation coverage. Finally, airways are used by ATC to establish orderly routes in busy airspace.
Remember how we used SkyVector’s sectional chart to navigate in Learning Flight 1? We can do the same thing to plan this IFR flight. Go to SkyVector and locate KJAC. However, instead of viewing the VFR sectional chart, click the "Enroute L-11" tab in the upper right-hand corner of the page.
The "L" in the chart name indicates that it depicts low altitude airways, also called Victor airways, which are used for flights below FL180. Just west of Jackson Hole, you’ll see IDA—the Idaho Falls VOR that is also one of the transitions on the ALPIN# departure. From there, V21 (and T331, the RNAV/GPS equivalent) connects IDA to the Pocatello (PIH) VOR.
You can plot this route on SkyVector using the "Flight Plan" feature by typing "KICNE" and "IDA" from the SID and then "V21 PIH":
Let’s look more closely at V21 between IDA and PIH. We can see the chart provides information about which VOR radials to track, the distances between waypoints, and the MEA to fly between the points that ensures obstacle clearance and radio reception.
Pilot TipIf you’re ever unsure about a symbol on a chart, just zoom out. Each SkyVector chart has a side panel with a legend explaining what each of the published symbols mean. You can also find more information on chart symbols in the FAA’s Aeronautical Chart Users' Guide.
For IFR flying, the same "direction of flight" rules apply to altitude as VFR, but 500 ft. is not added:
- For IFR flights eastbound (0° to 179° magnetic track), fly at an odd altitude (i.e. 7,000 ft. MSL; 11,000 ft. MSL).
- For IFR flights westbound (180° to 359° magnetic track), fly at an even altitude (i.e. 8,000 ft. MSL; 12,000 ft. MSL).
When selecting an altitude, look through all components of your route (the SID, airways, and STAR) and determine the lowest MEA. At KJAC, the ALPIN# departure requires pilots to maintain 15,000 ft. between KICNE and IDA. The V21 airway MEA is 7,000 ft. Finally, the BEARR# arrival has an MEA of 15,000 ft. until BEARR. Thus, although it would be possible to fly as low as 8,000 ft. along V21, you would just have to climb back up to 16,000 ft. before PIH.
The lowest safe altitude, corrected for direction of flight, is 16,000 ft., and that’s what we’re using as our cruising altitude on this flight.