UK MCA urges ships to prepare for navigation without GNSS

The UK Maritime and Coastguard Agency (MCA) is urging shipowners, operators, ports and maritime service providers to strengthen their preparedness for GNSS disruption, warning that jamming, spoofing or signal loss could affect navigation, communications, vessel tracking and other critical systems.

With maritime operations increasingly dependent on GPS and other satellite-based positioning, navigation and timing (PNT) services, the MCA says operators should not assume GNSS will always be available. Instead, vessels should be able to maintain safe operations using alternative navigation methods when satellite-derived information becomes unreliable or unavailable.

Understand where GNSS is being used

The first step is to identify how heavily a vessel or operation depends on GNSS.

GNSS inputs can feed a wide range of bridge systems, including ECDIS, AIS, radar, integrated bridge systems, autopilots, track-control systems, dynamic positioning and GMDSS equipment. The impact can also extend beyond the bridge to communications, timing systems, vessel tracking, port operations and logistics.

The MCA therefore recommends reviewing system architecture and data flows to identify equipment that could be affected if GNSS-derived PNT is disrupted.

Review risk assessments and contingency plans

GNSS loss should be treated as an operational risk rather than simply a technical problem. Ship operators should review existing risk assessments to determine what happens if positioning or timing information becomes unreliable.

Procedures should cover how interference is detected, who needs to be informed and how the vessel should continue operating safely.

Emergency preparedness and business continuity plans should also consider a prolonged GNSS outage, particularly for vessels operating in areas where interference has already been reported.

Make sure crews can recognise GNSS interference

Bridge teams need to understand that a GNSS signal can appear to be working while providing incorrect information.

Jamming can prevent or degrade the reception of satellite signals, while spoofing can provide false positioning information. This makes awareness particularly important: an apparently normal navigation display should not automatically be treated as proof that the underlying position is accurate.

Operators should ensure that bridge personnel understand the limitations of GNSS and know how to identify signs of unreliable positioning.

Cross-check navigation information

One of the MCA’s key recommendations is to use independent means of navigation and position fixing where practicable.

Depending on the vessel and operating environment, this can include radar-based navigation, visual position fixing, dead reckoning, estimated position techniques and celestial navigation.

The objective is not necessarily to abandon electronic navigation, but to ensure that crews have other reliable sources of information available when satellite-derived data becomes questionable.

Practise navigating without GNSS

Alternative navigation techniques are most useful when crews are familiar with them before an emergency occurs.

The MCA encourages operators to incorporate GNSS disruption into drills and training, giving bridge teams an opportunity to practise how they would respond to degraded or unavailable PNT.

This should include more than simply switching off a GNSS receiver. Exercises can examine how the loss of satellite positioning affects ECDIS, AIS, radar, autopilot, communications and other systems on the particular vessel.

Do not overlook shore-based systems

The risk extends well beyond individual vessels. GNSS disruption can also affect Vessel Traffic Services, port management systems, pilotage systems, search and rescue coordination, fleet tracking and automated logistics.

Ports, harbour authorities and service providers should therefore assess their own dependence on satellite-derived PNT and consider how a disruption could affect vessel movements and wider operations.

Communication between ships and shore-based stakeholders is particularly important where a GNSS outage could affect the information being shared between them.

Prepare for wider operational and financial disruption

The potential consequences of GNSS disruption can extend beyond navigation safety.

According to a 2023 UK government economic impact assessment cited by the MCA, a seven-day GNSS outage could result in estimated losses of around £183 million for shipping and £1.309 billion for port operations, with total estimated losses across the maritime sectors covered reaching approximately £1.5 billion.

This underlines why GNSS resilience is not only a bridge-management issue. A prolonged outage could disrupt vessel movements, port operations, logistics and other parts of the maritime supply chain.

Develop resilience beyond GNSS

Alternative PNT technologies are being developed as additional sources of resilience. These include eLORAN, VDES R-mode, 5G-based positioning, automated visual and celestial fixing, and inertial navigation systems.

The UK Government is also developing plans for a sovereign eLORAN network, with initial timing capability planned for 2028 and full positioning and navigation capability targeted for 2030.

However, many alternative technologies are still developing and may not be widely available in the near term. For vessels operating today, the immediate priority remains maintaining competent crews, effective contingency procedures and practical skills in alternative navigation.

Key recommendations for operators

The MCA’s guidance points to several practical priorities:

• Map GNSS dependencies: Identify every critical shipboard and shore-based system relying on satellite-derived PNT.
• Update risk assessments: Consider the consequences of both temporary and prolonged GNSS disruption.
• Strengthen detection procedures: Ensure bridge teams know how to recognise jamming, spoofing and unreliable positioning.
• Use independent checks: Cross-check GNSS information with radar, visual fixes, dead reckoning and other available methods.
• Train and drill: Give crews practical experience of navigating and operating when GNSS is unavailable.
• Review emergency plans: Include PNT disruption in emergency preparedness and business continuity planning.
• Coordinate with shore: Ensure ports, VTS, pilots and other service providers understand their own vulnerabilities and contingency arrangements.
• Keep alternative skills alive: Emerging technologies can strengthen resilience, but they do not remove the need for competent mariners who can navigate without GNSS.
• source : safety4sea