A huge area of the U.S. Southwest is under an flight advisory (PDF) warning of potentially unreliable GPS performance as unspecified "GPS testing" is carried out in the area of Truth or Consequences, N.M., from May 27-Jul. 1. It's not immediately clear if the advisory is related to LightSquared's ongoing program to test for interference resulting from its 4G broadband transmitters. As we reported last week, a LightSquared test program began in Boulder City, Nev., May 16 and continues to May 27 and the FAA warned that GPS disruptions might occur within a 330-nm circle around the test transmitter. Above FL 400, the area covered by the latest advisory will cover a circle 640-nm across centered 19 nm from the BVS VOR on the 230.5 radial.
The size of the affected area diminishes at lower altitudes but even at 50 feet AGL, the donut hole is 310 nm across. The flight advisory includes the proposed times for the tests but they are subject to change and anyone flying in that area and planning to use their GPS should be checking NOTAMs immediately prior to their flights.
Again, AVweb would be interested in hearing from pilots who think their GPS is affected by the test. Send your observations to firstname.lastname@example.org.