The US Maritime Administration (MARAD) issued an alert concerning reports of GPS spoofing in the Black Sea on the 22nd of June. At the time they characterized the report as “unsubstantiated.” On the first of this month, MARAD issued Maritime Advisory 2017-006 :

017-006-GPS Disruption-Global

1. Reference: U.S. Maritime Alert Message Reference Number 2017-005A.
2. Issue: During the week of 19 June 2017, a vessel transiting the northeast portion of the Black Sea reported multiple instances of GPS interference. More than 20 other vessels in the same area reported the same interference, which included an incorrect signal.
3. Guidance: Indicators of positioning systems interference include an intermittent signal, no signal, or an incorrect signal. Critical information to report during a disruption event includes: actual location (Latitude/Longitude), date/time, and period of outage and/or disruption. Additional background information on GPS interference and disruption is available at http://www.gps.gov/spectrum.
4. Contact Information: GPS disruptions or anomalies should be immediately reported to the U.S. Coast Guard Navigation Center (NAVCEN). Reporting a disruption – or other navigational hazards or aids to navigation outages – to NAVCEN can be done electronically through NAVCEN’s website at https://www.navcen.uscg.gov/?pageName=gpsUserInput or via phone at 703-313-5900, 24 hours a day. Reports will be disseminated to the U.S. Air Force GPS Operations Center and the Federal Aviation Administration in an attempt to identify the problem and correlate with any other GPS incidents in the same general geographic location.
5. Cancellation: This message will automatically expire on 01 March 2018.

—- Another good reference is the US Coast Guard “Trust But Verify” Marine Safety Alert 01-16 issued on the 19th of January 2016. Our thanks to Dennis Bryant and his newsletter for pointing this out.