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Can You Rely On GPS Alone?


Over the past 10 years, GPS has overwhelmingly become the preferred method of navigation, especially when it comes to IFR flying. The FAA's entire NextGen system is built around GPS, and almost all of us use it in some form.

But if you've gotten a briefing in the past year, you've probably noticed something that's been going on a lot: GPS NOTAMs like this...

What Are The NOTAMS For?

The FAA doesn't provide much detail, but the NOTAMS are for GPS interference testing. And when they're happening, you might not be able to use your GPS. At all.

Without spelling out every detail of the NOTAM itself (we have a course for that), the NOTAM states that GPS, including WAAS, GBAS, and ADSB, may not be available within a radius centered at the lat/long coordinates of 352252N 1163326W.

And the areas are big. From FL400 to an unlimited altitude, the radius is 359 nautical miles, decreasing in radius to 166 nautical miles at 50 feet AGL, with intermediate altitudes of FL250 (309NM), 10,000' (220NM), and 4,000' AGL (217NM).

The GPS testing for this particular NOTAM was from October 2nd to October 3rd, daily from 0430Z to 1330Z. And if you'd been flying in that area during the NOTAM's valid time, your GPS may not have worked.

How Can You Map Them?

So how can you map out these NOTAMS to see if your flight path might go through the affected area? The short answer is, you have to do some searching.

The GPS NOTAMS are provided textually, and the FAA distributes PDF files with a map on their Public Notices page, but not all of the NOTAMS are always listed on the page itself.

That's where searching comes in. In this case a, Google search of "NTC GPS 16-04" (that's found in the NOTAM itself) brings you to the FAA's flight advisory, complete with a map.

And with the map in hand, it makes it easier to visualize what the NOTAM really affects.

Do You Have A Backup Plan?

There's no restriction from flying through these NOTAM areas, but if you are, you should have a backup plan in case your GPS navigation fails.

Staying on Victor airways is one solution. Making sure you're within a VOR service volume if you're flying off route is another.

But if it's possible, the best solution is to avoid the NOTAM area altogether, and hope that there's less testing in the future.

Colin Cutler

Colin is a Boldmethod co-founder, pilot and graphic artist. He's been a flight instructor at the University of North Dakota, an airline pilot on the CRJ-200, and has directed development of numerous commercial and military training systems. You can reach him at

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