What happens when GPS goes down? Aviation’s backup plan explained
7 min read
Irish Torres, an aerospace technology writer at Safran Navigation & Timing, examines whether aviation’s existing alternatives to GPS can provide genuine operational resilience as interference becomes more common.
For most passengers, GPS happens quietly in the background.
It helps the aircraft know where it is, supports modern navigation procedures and feeds systems that have made flying more precise, efficient and predictable. And, most of the time, nobody thinks about it.
That is precisely the problem, and it is one the industry has been slower to confront than the technology itself would suggest. GPS resilience has largely been approached as a tick-box compliance issue rather than a design concern.
With GPS now integral to modern flight, its absence is almost unthinkable. Regulators increasingly recognise that interference is neither hypothetical nor confined to military operations.
The FAA warns that GPS is subject to both intentional and unintentional interference and advises pilots to be prepared to navigate their planes without using satellite-based navigation systems. The two principal threats are jamming and spoofing.
So when GPS fails, what exactly is the backup plan for aviation?
Yes, aviation has a backup
Modern aircraft are not expected to fall out of the sky simply because GPS becomes unavailable. Aviation has multiple alternative navigation capabilities, including inertial navigation systems, distance-measuring equipment, VORs and instrument landing systems.
In the US, the FAA explicitly requires many commercial operators conducting IFR operations to retain navigation capability independent of GPS, including DME/DME, inertial reference units or VORs for en route and terminal operations and VOR and ILS capability for final approaches.
The FAA also maintains its VOR Minimum Operational Network, or VOR MON, as a reversionary navigation capability during GPS disruptions. The network is designed so that aircraft operating within the continental US can use conventional navigation aids to reach an airport with a non-GPS instrument approach.
So the issue is not that aviation has no backup per se, but whether having a backup is the same thing as a resilient system. It isn’t, and treating the two as interchangeable is where aviation’s GPS planning falls short.
The backup is not the same as the primary system
This contrast matters because aviation has spent decades building around satellite navigation.
Performance-based navigation has enabled aircraft to fly more precise and efficient routes. GPS and other GNSS services support area navigation, required navigation performance and other elements of the modern airspace system.
The problem is that the systems designed to replace satellite navigation during an outage do not necessarily provide the same operational flexibility.
The FAA itself acknowledges that using the VOR MON during a GPS outage can involve more circuitous routes than GPS-enabled RNAV operations. An unscheduled outage can also increase workload for both pilots and air traffic controllers. That is an important distinction.
More aircraft may need additional separation. Controllers may face higher workloads. Flights may require rerouting. Airlines may face delays and increased fuel consumption.
A backup that keeps an aircraft safe is essential. But a resilient aviation system should also ask what happens when disruption lasts longer, affects a wider geographical area or occurs repeatedly.
GPS interference is no longer an edge case
For years, discussions about GPS disruption often focused on isolated outages, equipment failures or military operations.
That picture has changed.
ICAO has developed a specific roadmap on GNSS radio-frequency interference. Its immediate steps include supporting the safe continuation of aircraft operations during interference through contingency plans and increased awareness among flight crews and air traffic control personnel.
The fact that ICAO has developed a roadmap is significant.
It reflects growing recognition that GNSS interference is not merely an occasional technical inconvenience, but an aviation resilience issue.
ICAO’s longer-term approach goes beyond merely restoring GPS. Its roadmap calls for greater resilience through technological improvements to satellite navigation alongside independent timing sources and complementary positioning, navigation and timing capabilities.
That may be the most important shift in the conversation. But a roadmap is not the same as urgency, and the pace of interference incidents is arguably outrunning that of the response.
The future of aviation resilience isn’t about replacing GPS, but making sure it is never the only answer.
Aviation is moving from backup to resilience
Aviation already understands redundancy in almost every other critical part of the aircraft. Aircraft have multiple systems because safety cannot depend on a single component behaving perfectly forever. Navigation increasingly needs to be considered through the same lens.
That does not mean reinstalling every retired conventional navigation aid or abandoning satellite-based navigation. The answer will be more sophisticated than simply choosing between old infrastructure and new technology. It will involve combinations of satellite navigation, inertial systems, terrestrial navigation aids and other complementary sources of positioning and timing.
ICAO’s medium-term GNSS resilience roadmap points in exactly this direction. The organisation is developing a Resilient Navigation Operational Network concept intended to help states move beyond minimum navigation capability toward more resilient services that can maintain operational continuity during disruptions.
That phrase, operational continuity, may be the solution.
The main concern is not simply whether an aircraft can still find an airport when GPS disappears, but whether a highly interconnected aviation system can continue functioning safely and efficiently.
The risk is not that aircraft will forget how to fly
There is a tendency to make GPS disruption sound more dramatic than it is.
Commercial aircraft are not blindly following a blue dot on a map. Pilots are trained. Aircraft have multiple navigation systems. Air traffic control remains part of the system. Alternative procedures exist.
The danger is not that every GPS disruption creates an immediate catastrophe. The bigger risk is more gradual.
GPS dependence can become invisible. The more successful satellite navigation becomes, the easier it is to design procedures, infrastructure and operational practices around the assumption that it will always be available.
That assumption can quietly spread through an industry. Regulators bear some of that responsibility, as do airlines that have deprioritised non-GPS training and infrastructure investment because satellite navigation made it appear unnecessary.
One system depends on another. A new procedure replaces an older one. A navigation aid is retired because satellite navigation has made it less necessary. Training evolves. Infrastructure investment shifts.
None of those decisions is unreasonable on its own.
Together, however, they can make the absence of GPS increasingly disruptive. The real resilience test is not whether aviation can survive one outage, but whether the system has preserved enough independent capability to handle the next one.
Plan B should not be an emergency measure
The good news is that aviation is already addressing the problem.
The FAA requires non-GPS navigation capability for many commercial operations. ICAO is developing an international roadmap for GNSS interference resilience.
Regulators are treating interference as an operational challenge requiring procedures, awareness, reporting and alternative navigation capabilities, rather than solely as a technical problem for avionics manufacturers.
But aviation should be careful not to confuse contingency planning with resilience.
A contingency plan asks: What do we do when something goes wrong?
A resilient system asks: How much of the operation can continue when something goes wrong?
Those questions lead to very different investment decisions. The first produces a Plan B, whereas the second builds a system that does not depend on reaching Plan B before it is too late.
GPS is still essential, and aviation needs alternatives
The answer to GPS vulnerability is not to use less GPS.
Satellite navigation remains one of the most important technologies in modern aviation. It has improved efficiency, precision and safety and will remain vital to how aircraft navigate for decades to come.
But the more essential GPS becomes, the less aviation can afford to treat it as infallible.
ICAO’s current roadmap recognises that the future of aviation navigation will require more than simply protecting GNSS signals. It points towards a combination of stronger satellite-navigation capabilities, independent timing sources and complementary navigation technologies.
That is the right direction. But moving in the right direction is not necessarily moving fast enough, and aviation should not wait for a serious interference event to discover which applies.
The aviation industry does have a Plan B. It has VORs. DME. Inertial systems. Instrument landing systems. Air traffic control. Contingency procedures.
The real question is whether those systems are being preserved, modernised and integrated for the aviation system we are building, not the one we used to have.
GPS disruption is no longer a case of whether an aircraft can physically remain in the air. It is whether a global aviation system increasingly designed around satellite navigation can continue operating safely, efficiently and predictably when that navigation becomes unreliable.
Aviation knows how to fly without GPS. The challenge now is making sure it remains genuinely ready to do so.
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