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The guidance assumes GPS will fail. That tells you something

Qurexa Editorial Team6 October 20266 min read 0 0
The guidance assumes GPS will fail. That tells you something

What happened

On 1 October 2026 the Maritime and Coastguard Agency published Marine Guidance Note 719, or MGN 719. Its title is 'Operating in GNSS denied and degraded environments'. GNSS stands for Global Navigation Satellite System. It is the general term for the satellite networks that tell a receiver where it is. GPS is the American one, and the best known. Galileo is European, GLONASS is Russian and BeiDou is Chinese. Most modern receivers use several at once. The guidance is addressed to a wide group: shipowners, operators, masters, officers of the watch, harbour authorities, port operators, vessel traffic service providers, and anyone else who depends on what the industry calls PNT services. PNT stands for positioning, navigation and timing. The note's purpose is to help those organisations understand how vulnerable satellite positioning is, and to promote what the MCA calls operational resilience measures. In other words: plan now for the signal not being there. Denied and degraded are two different problems. A denied environment means the signal is being blocked, usually by jamming, which is simply broadcasting noise on the same frequency. A degraded environment means the signal is unreliable, which includes spoofing, where a receiver is fed a false signal and confidently reports a position that is wrong.

Why this matters

Satellite navigation is one of those technologies that became invisible because it worked. It is now built into things most people would never connect to space. Ships use it for position, but also for autopilot, for electronic chart systems, for collision avoidance systems and for the automatic identification signals that let other vessels see them. Ports use it for traffic management. And the timing signal, which almost nobody thinks about, is used to synchronise telecoms networks, financial transaction records and parts of the electricity grid. The weakness is physics. A GNSS signal has travelled roughly 20,000 kilometres from a satellite, and by the time it arrives it is extremely faint. Overpowering it locally does not require sophisticated equipment. For ordinary travellers, the maritime angle is the one that touches you most directly. Ferries, cruise ships and the vessels carrying almost everything in the shops rely on these systems. A guidance note telling bridge teams to prepare for operating without satellite positioning is, in effect, an instruction to keep traditional seamanship alive: paper charts, radar, visual bearings, and officers who can still fix a position without a screen. That is not a step backwards. Redundancy is what safety engineering looks like. The aviation and maritime worlds have always kept more than one way of doing the critical things.

What the evidence actually says

We should be careful about how far we take this, because the guidance note itself is measured. MGN 719 does not announce an incident, and the version we were able to review does not name specific locations where jamming or spoofing has occurred. It is guidance about resilience, aimed at a professional audience, not a warning about a particular event. Anyone presenting it as evidence of a specific threat in a specific place is going beyond what the document says. What is well established, and has been reported by maritime and aviation authorities internationally for several years, is that GNSS interference is no longer rare. It is also not always deliberate: faulty equipment, poorly shielded electronics and legitimate military exercises can all degrade a signal. The distinction between jamming and spoofing is the technically interesting part, and it matters for how you respond. Jamming is loud and obvious. Your position goes away, you know something is wrong, and you switch to other methods. Spoofing is the dangerous one, because the system does not report a failure. It reports a position, with apparent confidence, and that position is false. A navigator who trusts the screen has no immediate signal that anything is amiss. That is why resilience guidance tends to focus less on detecting interference and more on cross-checking: comparing satellite position against radar, against visual fixes, against the chart, against what the depth sounder says the water should be doing. If two independent methods disagree, you have learned something.

Practical advice

This guidance is written for mariners, and if you are one, MGN 719 is the document to read rather than our summary of it. For everyone else, there are a few sensible everyday habits that come from the same principle. If you are driving somewhere unfamiliar, know roughly where you are going before you set off. Satellite navigation failures on the road are usually mundane — no signal in a tunnel, a flat battery, a lost phone — but the fix is the same as at sea. Have a second method. A rough mental map and a note of the road numbers costs nothing. If you walk or cycle in open country, a paper map and a compass are still the only navigation tools that do not need power or a signal. Mountain rescue teams make this point every year, and they are not being nostalgic. If you are travelling by sea as a passenger, there is genuinely nothing you need to do. Commercial vessels carry multiple independent navigation systems and crews trained to use them, which is exactly what this guidance is reinforcing. And if you rely on a device for something that matters, such as a timed medication reminder, keep a backup that is not dependent on one app, one phone and one signal. A printed list or a pill organiser is unglamorous and it works in a tunnel.

What to know

The Maritime and Coastguard Agency published MGN 719, 'Operating in GNSS denied and degraded environments', on 1 October 2026. It is addressed to shipowners, masters, officers of the watch, harbour and port authorities and vessel traffic services. GNSS covers GPS and the other satellite positioning systems. Denied means the signal is blocked, usually by jamming. Degraded means it is unreliable, which includes spoofing, where a receiver is fed a false position and reports it confidently. The note promotes operational resilience rather than warning about a specific incident, and it does not name particular locations. Its practical thrust is cross-checking position against independent methods such as radar, visual fixes and the chart. The general principle holds well beyond shipping: if something important depends on one signal, have a second way of doing it. Sources: Maritime and Coastguard Agency / GOV.UK, 'MGN 719 (M+F) Operating in GNSS denied and degraded environments', 1 October 2026, https://www.gov.uk/government/publications/mgn-719-mf-operating-in-gnss-denied-and-degraded-environments ; Maritime and Coastguard Agency / GOV.UK, 'Active marine guidance notes (MGNs)', 1 October 2026, https://www.gov.uk/government/collections/active-marine-guidance-notes-mgns ; GOV.UK, 'Maritime and Coastguard Agency', https://www.gov.uk/government/organisations/maritime-and-coastguard-agency This article is for general information and does not replace advice from a doctor, pharmacist or other qualified healthcare professional, or professional navigational guidance for mariners.

#gps#navigation#maritime safety#technology resilience#shipping#ferries

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