GPS interruption notices are the official advisories and NOTAMs that warn users when GPS positioning, navigation, or timing (PNT) may be degraded, unavailable, or intentionally affected by coordinated testing. They come from a small set of government sources and have direct operational consequences for aviators, mariners, critical infrastructure operators, and field teams. This tutorial walks you through what those notices look like, where to find them, how to interpret the language, and step-by-step actions you should take when a notice affects your operation.

Who issues GPS interruption notices and why it matters

  • U.S. Coast Guard Navigation Center (NAVCEN) maintains public notices, active GPS service interruptions listings, and a GPS problem reporting channel for civilian users. NAVCEN also coordinates with other agencies when tests or exercises may affect GPS.
  • The Federal Aviation Administration (FAA) uses NOTAMs and flight advisories to notify airspace users about planned GPS testing or other events that can render GPS and WAAS unreliable or unavailable. The FAA’s Aeronautical Information Publications and guidance instruct pilots to check GPS/WAAS NOTAMs for route planning.
  • For maritime and general civil reports, NAVCEN accepts disruption reports and posts problem-report findings. For aviation-specific anomalies, pilots should use the FAA GPS anomaly reporting process. These reporting channels are the primary mechanisms the government uses to detect and correlate interference events.

How interruption notices are typically worded

Expect plain, direct phrasing. Examples you will see in official notices or NOTAMs include language like “GPS may be unreliable or unavailable” or “GPS interference will take place” with a geographic area and time window. When the government is conducting authorized GPS testing, the NOTAM will identify the test and provide points of contact or coordination instructions. Read these notices conservatively: they describe expected effects, not every conceivable receiver outcome.

Where to find official notices and status information

  • NAVCEN GPS Service Interruptions page: primary public listing of active notices and guidance for reporting. Use this first for non-aviation PNT problems and to check whether a known test is ongoing.
  • NAVCEN GPS Problem Report (online form): file a civilian disruption report with precise timing, location, device type, and symptoms. NAVCEN will review constellation and space weather and may coordinate with inter-agency partners.
  • FAA NOTAMs and FAA GPS Anomaly reporting: pilots should check preflight NOTAMs for GPS/WAAS testing and submit anomaly reports via the FAA GPS Anomaly form when they encounter in-flight degradation outside NOTAMed work or unexpected operational effects. The AIP and FAA guidance explicitly instruct operators to consult GPS/WAAS NOTAMs.

Quick operational checklist by user type

Aviation — preflight and in-flight

  1. Preflight: check NOTAMs and the FAA’s GPS advisories for your route. If a GPS testing NOTAM exists, expect degraded PBN and RNAV capability in the NOTAMed area and plan alternate navigation (VOR/NDB/INS/visual).
  2. If you experience real-time degradation or loss of GPS outside a NOTAMed area, advise ATC immediately, or if required, use the local ATC frequency to report the anomaly, then file the FAA GPS Anomaly report after landing. Include receiver make/model/firmware, number of satellites, time and position, and operational impact.
  3. If a safety-of-life operation is directly threatened during a coordinated test, ATC and NAVCEN maintain procedures to request a “cease buzzer” to stop testing for that mission. Keep the appropriate points of contact handy during operations in test-prone areas.

Maritime

  1. Check NAVCEN’s service interruptions page before transits in high-traffic or littoral regions. If you get unexpected GNSS loss, log time, position, receiver state, and cross-check with other ships or shore-based sources. Submit a NAVCEN GPS Problem Report after verifying the issue is not local receiver error.
  2. For critical navigation during loss, fall back to radar fixes, visual bearings, depth, and dead reckoning as appropriate. Avoid relying on a single PNT source for maneuvers in congested waters.

Land, infrastructure, and field teams

  1. For timing-sensitive systems, keep redundant timing sources and holdover references. If you see a localized PNT outage, collect logs from multiple devices, note symptoms (noise floor increase, abrupt loss, time slips), and report to NAVCEN for correlation. NAVCEN will check constellation and space weather and may link multiple reports.
  2. If you suspect illegal jamming or an unauthorized transmitter, report to the FCC tip line or local enforcement. Jamming devices are unlawful and the FCC maintains resources for public reporting. Prompt reporting helps enforcement and system-level characterization.

Field diagnostics to run before you report (practical, repeatable steps)

  1. Reboot the receiver or device. Many software receivers recover after a power cycle.
  2. Cross-check another device or a smartphone receiver to see if the effect is device-specific.
  3. Note satellite count, PRNs in view, SNR values, and RAIM/receiver integrity flags. If available, capture NMEA logs or binary logs and UTC timestamps. These are extremely valuable to NAVCEN/FAA investigators.
  4. Record the exact start/stop UTC times, latitude/longitude of the problem, and any unusual RF noise observed with spectrum-monitoring gear if you have authorization to operate it.

How to file a good report (what NAVCEN and FAA need)

  • Time in UTC, precise location, device make/model/firmware, number of satellites tracked, descriptive symptoms (e.g., total loss, position jumps, timing slips), estimated duration, and operational impact. Include any mitigations you used. Both NAVCEN and FAA forms list these fields. Be concise and factual.

Mitigation and resilience recommendations (engineering and operational)

  • Always plan redundant navigation: dual-constellation GNSS with SBAS where available, inertial navigation for short-term holdover, and conventional navaids for terminal ops. Use receiver features like RAIM and multi-antenna attitude checks when available.
  • For timing-critical infrastructure, add disciplined oscillators and holdover strategies so short-duration GNSS outages do not upset operations.
  • For persistent or repeated interference in a region, coordinate with spectrum authorities and NAVCEN so that the pattern can be analyzed and correlated with other reports. NAVCEN’s GUIDE tool and problem reports help build the operational picture.

Legal and coordination notes you must keep in mind

  • Authorized GPS testing by U.S. federal entities is normally coordinated and publicly notified in advance. Those tests may be stopped for safety-of-life operations, but cancellation is reserved for compelling reasons. That coordination is why you will see scheduled GPS testing NOTAMs rather than unexplained, ad hoc shutdowns.
  • Unauthorized jamming is illegal and harms emergency communications and public safety. If you have reason to believe an interference source is unauthorized, report it to the FCC in addition to NAVCEN or FAA as appropriate. Timely public reports make enforcement and mitigation possible.

Final operational tips

  • Don’t assume every notice will affect every receiver in the same way. Receiver antenna, filtering, firmware, and multi-constellation capability change the real-world result.
  • Treat any GPS interruption notice as a trigger to switch to a tested contingency procedure. Train to operate without GPS; practice dead-reckoning, nav-aid approaches, and other non-GNSS skills regularly.
  • When in doubt, report. Even a single, well-documented report can help NAVCEN, FAA, and enforcement agencies correlate an otherwise opaque event and protect others.

If you want a short printable checklist for preflight, bridge watch, or field teams I can produce one tailored to your equipment and operations.