If you’re flying the Great Falls area (KGTF) from now until March 6th, you’ll want to watch out for some GPS outages due to testing.

Right now, they’re testing daily from 1631z-20z, and the impact is all about how high you’re flying. You could lose WAAS, GBAS, and ADS-B.

See the ranges here:

If you do experience outages, you’re asked to only contact ATC if you’re in need of assistance, not to report any outages.

NOTAM INFO: NAV GPS (AFSMO GPS 18-04) (INCLUDING WAAS, GBAS, AND ADS-B) 
MAY NOT BE AVBL WI A 361NM RADIUS CENTERED AT 470259N1103758W (GTF115040) 
FL400-UNL, 
302NM RADIUS AT FL250 
222NM RADIUS AT 10000FT 
213NM RADIUS AT 4000FT AGL 
162NM RADIUS AT 50FT AGL.

The full FAA text is here: https://www.faasafety.gov/files/notices/2018/Feb/AFSMO_18-04_GPS_Flight_Advisory.pdf