MGN 719: What the MCA Wants Bridge Teams to Do When GNSS Fails

Why This Note Exists

Almost every navigational and communications system on a modern ship takes a position or a time from GNSS (GPS, Galileo, GLONASS, BeiDou). The MCA's new note records a marked increase in interference reports in recent years, particularly in the Black Sea, the Baltic, the Gulf and East Asia, and asks the whole industry to plan for operating when that signal is degraded or gone.

The note uses two terms you should be able to explain to a junior officer:

• Jamming — the signal is blocked or degraded, so receivers lose position or lose accuracy.
• Spoofing — false position information is presented to the user. This is the more dangerous of the two because the display still looks normal.

What Can Go Wrong On Your Ship

MGN 719 lists the shipboard systems that depend on external position, navigation and timing (PNT) data. The list is longer than most bridge teams expect:

• ECDIS, GNSS receivers and integrated bridge systems
• AIS, and radar functions that take a GNSS input
• Track control systems and autopilots
• Dynamic positioning systems
• Gyro compasses and voyage planning / route monitoring systems
• GMDSS equipment and pilot portable units (PPUs)
• Timing-dependent systems: networks, data systems using NTP/PTP synchronisation, and anything that relies on UTC

Ashore, the same dependency affects VTS, port management and pilotage management systems, LRIT, search and rescue coordination and fleet tracking. The note also covers fishing (net plotters, gear monitoring) and offshore work, including survey-grade GNSS and RTK.

What The MCA Recommends

For companies and operators, the note recommends that you:

• Review risk assessments for GNSS degradation and denial.
• Identify which critical systems depend on external PNT data, including architecture, data flows and interfaces.
• Establish procedures for detecting and responding to GNSS interference.
• Make sure bridge teams and operational personnel understand the limitations of GNSS.
• Verify navigational information by independent means where practicable.
• Exercise contingency procedures in drills and training.
• Consider PNT degradation within emergency preparedness plans and business continuity arrangements.

For mariners, the central message is that you should exercise the ability to navigate safely using alternative sources of navigational information. The note names radar navigation and position fixing, visual navigation, celestial navigation, dead reckoning and estimated position, and independent sensor systems.

What It Does Not Do

It is worth being clear about the limits. MGN 719 is advisory. It does not set out detailed bridge team procedures, equipment specifications, a training syllabus, mandatory passage planning steps or a reporting procedure. That detail is left to companies to build into their own safety management systems, which makes this a prompt to do that work rather than a finished procedure you can adopt unchanged.

The Bigger Picture

• The note cites a 2023 DSIT impact assessment estimating that a seven-day GNSS outage could cost around £1.5 billion, with ports (about £1.3 billion) and shipping (about £183 million) the most exposed.
• The UK intends a sovereign eLORAN network as a terrestrial back-up, with initial capability targeted for 2028 and full operational capability by 2030.
• Other alternatives under development include VDES R mode, 5G, automatic visual and celestial fixing and inertial navigation. The MCA's stated aim is to have PNT sources with failure modes different from GNSS's. None is available at scale yet.

What This Means On The Bridge

The note stops short of telling you how to run a watch. These are practical habits, Crew Connect's own suggestions for putting its principles into practice:

1. Never let GNSS be the only fix. Cross-check it against radar ranges and bearings, visual bearings and depth soundings at a frequency suited to the waters you are in.
2. Know what a bad fix looks like: a position that jumps, speed over ground that disagrees with log speed, course over ground that does not match the heading, AIS targets that scatter or sit in impossible places, and time errors.
3. Brief it before you need it. Agree in the passage plan what you will do on suspecting interference: who is called, what the fallback fix method is, and when to slow down.
4. Watch the track control. An autopilot following a spoofed position will steer confidently to the wrong place. Be ready to take manual control.
5. Practise it. A GNSS-loss drill on a quiet watch is cheap. Doing it for the first time in a congested strait is not.

Try the Decision Simulator

What would you do when the ECDIS position jumps three miles in a minute? This is a fictional training scenario, not a real incident. Work through it in the free Decision Simulator — no login needed to preview.

Test Your Knowledge

Think you've got this covered? Put it to the test in Crew Connect's free Knowledge Checker — try a quick navigation round and see how you score.

Related Reading

• What Would You Do If GPS Failed Right Now?
• Black Sea: Drone Strikes and GPS Interference (Liberia MSB 38/2026)
• Week 41 2026 regulatory roundup