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IFR Fix: Back to the cone of confusion

What's your destination if the evaluator for your instrument-rating practical test or proficiency flight calls for requesting a diversion to the nearest “MON airport”—and what approach might you have to do when you get there?

The airports of the Minimum Operational Network are identified on IFR navigation charts with "MON" above the airport name. Image courtesy of SkyVector.

Here’s a hint about the approach: It won’t involve GPS.

Although such a scenario could arise, you’re not likely to have to fly the clearance in training because MON airports are few and far between—perhaps 100 miles away. Look for the “MON” designation above an airport’s name on low-altitude en route charts.

MON-designated airports were selected for inclusion in the Minimum Operational Network because you can navigate to them for a safe landing using only “legacy” procedures—that is, without reliance on the Global Navigation Satellite System (GNSS). (See Aeronautical Information Manual Section 1-1-3.) That old-school capability is your “out” in case the NextGen-based navigation system were to experience, to use the FAA’s word, a “disruption.”

Well, instrument flying is all about contingency planning. If you needed a reason to practice VOR course tracking, radial intercepts, identifying airway intersections using another VOR’s crossing radials, holding, and approaches—remember what it’s like to overfly the “cone of confusion” and to time the leg from the final approach fix to the missed approach point with a stopwatch?—now you have one.

Our readers, responding to our reporting on the importance of limiting the impact of intentional GPS outages implemented by the Pentagon for defense-readiness training exercises, have been emphatic that any service disruption, planned or inadvertent, must have a clear “out” available for any flight caught up in it.

So it couldn’t hurt to simulate that scenario by mock-diverting to a MON airport and flying some procedures the old-fashioned way.

Note operational limitations: “Navigation using the MON will not be as efficient as the new [performance-based navigation] route structure, but use of the MON will provide nearly continuous VOR signal coverage at 5,000 feet AGL across the [national airspace system], outside of the Western U.S. Mountainous Area.”

That design ensures “that regardless of an aircraft’s position in the contiguous United States,” an airport with legacy approaches “will be within 100 nautical miles.” A charted MON airport is Greater Binghamton/Edwin A. Link Field in Binghamton, New York.

In the era of glass cockpits, PBN, and direct routings, MON airports are need-to-know information for your IFR flight planning, as are the instrument procedures awaiting you there.

Dan Namowitz
Dan Namowitz
Dan Namowitz has been writing for AOPA in a variety of capacities since 1991. He has been a flight instructor since 1990 and is a 35-year AOPA member.
Topics: IFR, Training and Safety, Flight Planning

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