Rise of GPS Interference Raises Concerns for NextGen

 - April 2, 2012, 4:15 AM

Today, most of us would probably rate cellphones, ATMs and the Internet as the three most useful modern gadgets we use regularly. We likely wouldn’t rank GPS up there, and maybe not even in the top 10. Yet without GPS, those three wouldn’t work too well, if at all, and neither would a host of other things that we depend on (reliable electrical power; banking systems; national and worldwide telecommunications, including air traffic control; and car navigation, to name a few). And with NextGen slowly approaching, aviation’s dependence on GPS will grow exponentially.

But their dependability is not assured for the future. Considering their importance, the GPS satellite signals are improbably weak: someone compared them to detecting a Christmas tree light bulb in New York, when viewed from Los Angeles. The reason is that in the 1970s USAF developers had classified technology that could hide them from adversary detection deep in the atmospheric “noise.” But parallel civil technology eventually caught up and public GPS access was granted in 1983. On Sept. 10, 2001, the Department of Transportation warned that the weakness of the signals made them vulnerable to deliberate jamming. Events the very next day demonstrated the reality of ill intent.

Today, the worldwide GPS market and the system’s applications have expanded beyond anyone’s imagination, with the number of receivers in use estimated to be “close to half a billion.” Accompanying the rise in GPS usage have been ever increasing reports of signal interference and jamming. One UK report stated that over a six-month period in 2011, twenty dedicated GPS signal monitors spread across the country had recorded between 50 and 450 deliberate interference events every day. Of these, almost all were attributed to small, low-powered devices selling for around $50 on the Internet since, as in the U.S., GPS jammers are illegal in the UK. Nevertheless, several thousand are reportedly in use in Britain and more than100,000 in the U.S., their main purpose being to defeat GPS tracking systems installed in trucks by their company owners. But their numbers are said to be steadily increasing and, unfortunately, their low power levels make them difficult to detect, especially in moving traffic. Last November, the Department of Homeland Security reportedly introduced a U.S. nationwide GPS monitoring project called Patriot Watch, similar to the system in the UK.

What does GPS jamming mean for aviation? Because the most common jammers today are low powered, their main threat is to lower-altitude aircraft on a GPS, GPS/Waas or GPS/RNP approach and on the airport surface, where GPS-driven airport maps are being used. AIN reported last year on the collateral jamming of the ground-based augmentation system (GBAS) at Newark, which suffered random and unpredictable shutdowns that were eventually found to be caused by jammers in trucks travelling along the nearby New Jersey Turnpike. The only cure for the problem was to move the four GBAS antennas farther infield to a point out of range of the jammers.

But this is unlikely to be a permanent cure. Inevitably, under a “bigger is better” mindset, some buyers will feel more protected with a more powerful, longer-range jammer, and these too are now available on the Internet. This of course raises the threat level since, depending on their antenna configuration, they increase the likelihood of higher-altitude interference, with a consequent impact on ADS-B.

Is There Safety in Numbers?

Will other, more recently assembled GNSS constellations such as Europe’s Galileo be less affected by GPS jammers? The answer, unfortunately, is no. All GNSS satellites transmit in the same quite narrow set of frequencies, with each satellite assigned a unique coded ID. On the plus side, the DOD’s next-generation GPS III will transmit more powerful signals than at present, but jamming follows the military practice of escalating countermeasures as the adversary increases his.

It was also once felt that when Europe and China joined the U.S. and Russia with full worldwide GNSS constellations, along with smaller regional constellations over India and Japan, the 130 or more satellites would always provide superior performance by allowing user receivers to select the optimum satellite geometry, with maximum redundancy. That is still true, but with all those satellites continuously transmitting, initial recent research suggests that the ambient atmospheric noise “floor” also rises, potentially further weakening those already weak satellite signals, to the jammers’ advantage.


Spoofing is an essentially military technique that can allow control of a UAV to be taken over electronically in flight and directed elsewhere on false GPS data. Earlier this year, Iran claimed that it used spoofing to capture an unmanned U.S. RQ-170 Sentinel, a claim the USAF has challenged. However, the fact that it appears to have made a successful wheels-up landing with relatively little damage has created concern in the Pentagon and elsewhere, since both Russia and China are known to have conducted extensive spoofing research. Spoofing is a complex process and, as far as is known, has not been achieved with an unmanned aircraft in the West. If Iran’s claim is true, it would have a profound effect on future unmanned aircraft warfare strategies.

The Future of Aviation GPS

Unquestionably, GPS jamming will increase and, as we move further into a satellite-based NextGen environment, its interference will become more noticeable. This raises two key questions (not only for NextGen but also for all other critical GPS applications). For aviation, will GPS reach the point of no longer being totally dependable? Second, if so, are the backup systems proposed for NextGen adequate for the long-term future?

AIN will explore some of the options ahead in a future issue.


And this is news??? More like "Duh, where's my V-8!"
Drives me nuts. These discussions were in play over 30 years ago - now we're treated to an Valley Girl's "OMG"! How about a LOL and BTW "told you so"! Isn't anyone thinking out there???

GPS wasn't being bet/relied on for the futrue of civil aviation 30 years ago. You said "Isnt anyone thinking out there??" the answer is yes. People are thinking out there. feel free to join in anytime.

GPS wasn't being bet/relied on for the futrue of civil aviation 30 years ago. You said "Isnt anyone thinking out there??" the answer is yes. People are thinking out there. feel free to join in anytime.

Sometimes, before using a term you are a apparently unfamiliar with John, a Google search (http://en.wikipedia.org/wiki/Spoofing_attack) can help prevent you from undermining your credibility.

We HAD a perfectly good terrestrial backup system in place - LORAN. The proposed upgrade never took place and instead the gov't saved a few bucks by decommissioning it. The idea that the entire air transportation system should rely solely on a sat-based system is simply not well conceived.

I started out in avionics maintenance in the 1970s and moved into the satellite communications business as an electrical engineer in RF electronics. As a pilot, the decades-long push to all-GPS navigation has troubled me for quite some time.

The flying public (pilots and pax alike) do not realize just how fragile the GPS signals are; they are far, far more vulnerable than VORs, NDBs and LORAN. In the event of a national crisis (pick one) the GPS availability may well not be there. Its akin to depending on one little paper match in your winter survival kit; you hope it's never needed because it's all you've got. Distributed systems like VOR/TACAN are much harder to knock out as they are widely disbursed, operate on multiple frequencies, are independently powered, and transmit with dozens of watts in the local area, not faint signals arriving from points some 23,000 miles into space. In contrast, GPS depends on a handful of extraordinarily low-power transmitters that are highly exposed to all enemies and are incapable of being defended.

LORAN was a good thing (especially after good microprocessors came about to simply its use) but short-sighted politicos nixed all that. Even NDBs do a good job; they are widely used in developing countries for minimal cost. During a national defense crisis, I would rate the NDB as more trustworthy than GPS, but its not as sexy, so you can forget about that being funded!

Correction: GPS satellites are not 23,ooo miles in space (as the geosynchronous satellites are; my mistake). They operate about half that height (12,600 miles) but are just as vulnerable.

@readerPDQ - I believe you are correct wrt LORAN being a lost opportunity. I had a LORAN receiver, before I replaced it with a GNS530, and it worked well. The upgraded eLORAN would have worked much better. I believe that even now it would be possible to reinstate the eLORAN chains. The various manufacturers of GPS aviation units could provide for an upgrade to provide moving maps and navigation using both GPS and eLORAN in the same box (or an external eLORAN receiver providing location to the GPS box). That would be a great navigation backstop, providing a combined satellite and terrestrial based system.

This is why we need to keep the VORs arround, even if it means putting off Next Gen tech for a TBD amount of time if money needs to be saved

I totally agree with Kevin's comment. I believe that we are opening ourselves up to potential disaster without a reliable navigation network as backup to GPS. Loran is gone and apparently there is a plan to decommission VOR's, leaving us dependant on GPS with all its weaknesses.

I am a flight instructor and can tell you that General Aviation is taking a tremendous hit with the advancement of the Next Gen system. I am all for flight safety and high tech., but I also realize that we had a very good system in the Loran and VOR system. The NDB for many pilots was a challange, but it made them think! Take a new "glass cockpit" aircraft and turn off the GPS and you would be surprised as to how many pilots have a tough time just trying to figure out where they are at!
There are getting to be fewer and fewer general aviation aircrafts flying. One of the main reasons is the "Cost" of fuel and upgrades required to continue to operate within the system. I wounder if some of our FAA personell as well as our elected officials that make these decisions realize that "their job" also depends on the health of general aviation. My view - Use the GPS, but keep what we have and re-instate the "loran system". Seems that the government has no problem dumping "Billions" into foreign "black holes", but cannot afford to take care of a system that we already have.

I agree....LORAN should never have been shut down. Fortunately, there are some key stations still "up." The facility at Caribou, ME is in "hot standby"...ready to turn on with some notice. I don't know how many others are in this condition, but it's a pretty good bet that there are some, due to the nature of how LORAN works. The LORAN errors that were frequently mentioned as a reason to move to GPS, primarily existed only on the ground or in the water....based on terrestrial based interference, affecting mostly boaters. Terrestrial based NAV systems will always be more reliable because humans can get to them for repair. VOR, ILS are still valuable and necessary aids. Even the lowly NDB has it's place, but alas, they are being shut down as a result of budget, aging and short-sightedness.

Would the ability to frequency hop solve the problem?

Just to make the point: GPS was all about global navigation infrastructure - for multitudes of users - even though justified as mil-based originally in concept. IT WAS in the concept of operations to be a major player in civil aviation - guess you had to be there - but that was 40+ years ago so many wouldn't have been. By 30 years ago there WERE major questions about "total" reliance on any space-based system - specifically for the military - but also as was being considered in civil aviation concepts and designs.

But deal with the real question - when was it a ever a good idea to put all of our eggs in one basket?

BTW - LORAN lives in reverse as a “Back to the Future” concept. They canned LORAN (really dumb ... but it was a "had to be" to justify moving on - NextGen part of that logic - among other things). But wait ... then they re-invented LORAN by reverseing a old NAV CONOPS into a "new" surveillance CONOPS called ref Wide Area Multi-Lateration (WAM) where the transmitters are airborne/mobile and the receivers became fixed-site clusters on the ground. Good thinking in some ways - but not good strategy as WAM too is ultimately dependednt on GPS.

The thread below has it right - LORAN (updated) was/would be the best primary system - with GPS as back-up.

Also makes me wonder what part of the funny farm some peple live on to hear we won't need PSR/MSSR capabilities - as one hears from many who default to GPS derived uber alles systemics. Well, you darn well might when GPS/GNSS becomes unusable as several realistic scenarios point out is not only possible but even likley.

Unfortuneatly, it will take a disaster before the politicians will consider the danger of the current scenario. They aske the quesiton, "What is the likelihood that an event will transpire?" and then assign a probability cost to that scenario. If it costs more to address the potential scenario than the scenario costs, it will be ignored. It will take a disaster and the political fall out to see action on this issue. And that's unfortunate for all the people who may be affected when that disaster becomes reality.

What GPS backup is ready now with USA wide coverage and not "a plan in the FAA or DHS thought process"?