A notice from the Federal Aviation Administration warns of the possibility that GPS signals may become unavailable or unreliable. This is due to tests performed by the Department of Defense from January 20 to February 22, 2011.
While this may not affect the average GPS user, those who rely heavily on their PNDs on a daily basis may find these interruptions bothersome.
From the Department of Defense:
A. Location: Centered at 304906N/0802811W or the location know as 105.25 degrees and 52.1 NM from the SSI VOR.
B. Dates and times: GPS testing is scheduled on January 20th through February 11th, 2011 from 0000-0245 UTC daily and February 15th through February 22nd, 2011 from 0000-0245 UTC daily. These tests may not be concurrent so pilots are advised to check NOTAMS frequently for possible changes prior to operating in the area.
C. Duration: Several test events will be conducted and will be active for 45 minutes followed by 15 minutes of off time.
D. During testing, GPS will be unreliable and may be unavailable with in a circle with a radius of 370NM and centered at 304906N/0802811W or the location known as 105.25 degrees and 52.1 NM from the SSI VOR at FL400; decreasing in area with a decrease in altitude to a circle with a radius of 325NM at FL250; a circle with a radius of 260NM at 10,000FT MSL and a circle with a radius of 215NM at 4,000FT AGL.
E. Pilots are highly recommended to report anomalies during testing to the appropriate ARTCC to assist in the determination of the extent of GPS degradation during tests.
Original article by: https://www.faasafety.gov/files/notices/2011/Jan/G.