8 min read

2018 is a year of milestones for the Global Positioning System (GPS). The concept of navigating by satellite was first discussed in the early 1960s, but it was exactly 40 years ago that the Department of Defense launched the first fully-functional NAVSTAR satellites into orbit. It remained a somewhat obscure military project until the early 1990s, when portable GPSs began to show up from famous brands like Sony (remember the Pyxis GPS?) and startups like Magellan (remember the NAV 1000?).

It was Garmin that really changed the aviation industry, though, with the introduction of the GNS 430 and 530 twenty years ago. Even jaded old veterans had to admit that a color moving map that always knew your position and groundspeed was pretty impressive, and it ushered in a new era of direct-to navigation and GPS approaches. Over 125,000 430s and 530s were sold before the GNS line was discontinued in 2011.

Decades after it first caught on, GPS is so deeply embedded in everyday life that we now take it for granted. Over two billion people carry around smartphones with GPS receivers inside, enabling everything from Uber to Instagram. As life-changing as these services have been, it’s hard to think of an industry more transformed than general aviation. Consider the long list of capabilities that even a 60-year old Light Sport Aircraft can now have thanks to 24 satellites.

Nobody gets lost anymore

GPS satellite

Everything changes when the navaid is in space.

At its most basic level, GPS does only one thing: it tells the user exactly where they are. That deceptively simple feature unlocks so much more when paired to a navigation database and a large screen, but even the basic lat/lon location is a huge benefit for pilots. Before GPS, lots of brain power was required just to understand where the airplane was, especially when flying in clouds. Dead reckoning skills, VORs, NDBs, DME and radar were all used to answer the question, “where are we?” Even with all that technology, getting lost was a major concern. When I began my pilot training in the mid-1990s, we spent a lot of time discussing “lost procedures,” which included everything from circling water towers to asking for a DF steer.

Those conversations seem quaint now. Sure, you can lose situational awareness (usually due lack of proficiency with avionics), but truly being lost for a long period of time is almost unthinkable. The panel-mount GPS will show you where you are and where you’re going. If not, the portable GPS will… or the tablet… or the phone. Maybe this has made our pilotage skills a little rusty; it has also prevented countless accidents.

Navigation doesn’t just mean in flight, either. Geo-referenced taxi diagrams have become mainstream with the growth of the iPad, and have played at least some role in reducing serious runway incursions. Consider the famous (and frightening) incident at Providence, Rhode Island, when a 737 was cleared to take off directly into the path of another airliner that had strayed onto the active runway. Today, both crews would most likely know right where they were thanks to GPS, and they might even have a display of ground traffic to complete the picture.

Instrument approaches to small airports

Once a flight reaches the terminal area, the navigation challenge gets even more acute, at least when it’s IFR. Major airline airports have always been well served by ILS approaches that can guide an airplane down to 200 feet AGL, but smaller airports (where most general aviation pilots fly) had to make do with worse options – maybe nothing more than a circling VOR approach or an NDB approach.

GPS has fundamentally changed the distribution of power. Because WAAS GPS approaches depend on a single constellation of satellites instead of hundreds of locally-installed radios, a quiet country airport can have the same precision approach that a major towered airport does, complete with a glideslope down to 250 feet. There is a cost to creating an approach, but it’s far less than installing a full ILS. The proof is in the numbers: today there are almost 4,000 WAAS approaches, over 1,000 at airports not served by an ILS. Score one for the little guy.

Terrain and obstacle alerts

Garmin terrain alert

Terrain alerts were once found only in airliners; now they are included with most aviation apps.

Most pilot intuitively know that these navigation tasks are easier with GPS, but what’s less appreciated are the huge advancements in hazard alerting that have come about. Throughout much of the 1970s and 1980s, Controlled Flight Into Terrain (CFIT) was a leading cause of fatal accidents, with the American Airlines crash in Cali, Colombia a more recent example. That Boeing 757 had a basic Ground Proximity Warning System (GPWS), but it only gave the pilots a 12-second warning before impact with a mountain. Modern Enhanced Ground Proximity Warning Systems (EGPWS) use GPS to provide much more sophisticated alerts, and critically, they also provide a visual overview of terrain. They have been spectacularly successful, almost eliminating CFIT accidents in properly equipped airplanes.

The latest advancement has brought this technology to consumer devices. An iPad running ForeFlight or Garmin Pilot can provide not just terrain alerts but also obstacle warnings. Some avionics even show power lines, a critical feature for helicopter pilots and crop dusters. Without GPS these alerts would be either impossible or annoying to the point of uselessness.

Traffic and weather

GPS isn’t the essential technology behind traffic alerting; after all, radar kept airplanes separated for decades before it was invented. What GPS has added is another level of precision and a lower cost of entry. Instead of spending $20,000 or more to install an active traffic system (or a full-blown TCAS), ADS-B traffic can be displayed on an iPad for well under $1,000. And instead of just showing position and altitude, ADS-B traffic can also show track and speed. This means pilots can make smarter deviations based on where a threatening airplane is going, not just where it is.

Datalink weather has been even more widely adopted than traffic alerts, with tens of thousands of pilots now flying with up-to-date radar images received via SiriusXM satellites or ADS-B ground stations. This is beginning to show up in the weather accident rate, which started declining around the time when ADS-B weather went mainstream. Again, GPS is not the main technology at work here, and yet it’s impossible to imagine modern datalink weather without it. A static radar picture in flight is nice; having your position and route as well makes it far more valuable. The big picture awareness is what makes strategic avoidance so easy. It’s not just radar, either. Imagine trying to avoid a temporary flight restriction (TFR) without GPS on board.

The future

Is the GPS revolution running out of steam? Not yet. The latest generation of GPS satellites, called Block III, are scheduled to launch in October, which should bring improvements in accuracy and availability. Beyond fundamental system upgrades, there are plenty of exciting projects in the works, many of them outside aviation. These include everything from detecting seismic activity to tracking shipping containers with pinpoint accuracy.

In aviation, the most visible advances will come from the world of ADS-B. While the FAA’s mandate has been a source of frustration for many pilots, this massive program will slowly transform how air traffic control works. By connecting a WAAS GPS to an upgraded transponder, ADS-B offers coverage in many places that radar could never reach, and usually with better accuracy. It’s even beginning to change airspace, as routing and frequencies are redesigned around GPS navigation instead of VORs.

RNP approach

An instrument approach that is only possible with GPS.

Pilots can also expect to see more WAAS approaches to remote airports, many of them in places where traditional navaids are simply impractical. The latest RNP approaches feature curving paths and multiple step down fixes, designs that are only possible with very precise GPS receivers.

Another interesting idea is the creation of more data-driven safety programs that use GPS flight data recorders to analyze flights and identify potential safety issues. Such programs have made a difference in the airline industry, and inexpensive GPS receivers might make them practical for GA pilots too. Perhaps GPS could even begin to make a dent in the number of fuel exhaustion accidents, by showing real-time range graphics and more accurate time en route numbers, although that may be wishful thinking.

As magical as GPS seems, it is obviously not perfect. Much of the behind-the-scenes work going on now is focused on protecting it from interference, either intentional or accidental. This is a small but growing problem, as it’s shockingly easy to spoof a GPS receiver. The more our world relies on GPS, the more critical this problem becomes.

Unfortunately the bigger threat, as you might expect, comes from pilots. GPS is merely a tool, not a replacement for a competent pilot. Used wisely it can improve situational awareness and increase safety margins; used carelessly it can lead to disaster. Indeed, the key mistake made by the pilots in Cali was to mis-program their flight management system. This is a reminder that avionics proficiency is an essential skill in the modern cockpit, not a bonus.

Still, 40 years after the Department of Defense launched NAVSTAR and 20 years after Garmin launched an avionics boom, GPS deserves the prize for the most significant innovation in aviation history. One key reason it has had such an impact is its wide reach – unlike say, the jet engine, it has touched all parts of aviation. GPS has been a democratizing force, both adding features and reducing cost for pilots all around the world. Here’s to 40 more years of saving lives.

John Zimmerman
6 replies
  1. Kim Hunter
    Kim Hunter says:


    Thanks for a nice review of the improvements in flight safety brought about by the GPS revolution. I think the availability of vertical guidance during non-precision LNAV approaches is another huge benefit of WAAS-capable receivers.

    Although ATC privatization seems to be interred for the time being, it is important to remember that the airline industry fought hard to derail the development and implementation of GPS WAAS technology – and ADS-B which requires WAAS capability. There were two reasons. First, airlines (mistakenly) invested heavily in PBN navigation technology for a decade. Technology that was less accurate than WAAS and required special crew certification to fly approaches. That said, it possessed the virtue of effectively restricting GA IFR operations at airports served by PBN approaches. The second reason was the airlines’ discomfort at the proliferation of precision WAAS approaches to GA airports. These approaches were quick and easy to design and relatively inexpensive to certify. They threatened to become the new IFR standard. The airline lobby went as far as pressuring congress to discontinue developing WAAS approaches at GA airports, maintaining it was a waste of scarce FAA resources.

    Whatever you think of ADS-B, I believe we owe a debt of gratitude to the FAA for staying the course and ensuring that all of us reaped the benefits of WAAS GPS.

  2. Duane Mader
    Duane Mader says:

    Interesting Kim. Airlines SHOULD be happy that GA pilots can stay away from major airports using GPS approaches.
    On a side note, I think corporate pilots could help prevent the privatization push from airlines by staying away from major hubs if possible. One corporate pilot I talked to took his passengers to Denver (KDEN) because “his passengers wanted to go to Denver”.
    Educate the pax that going into eg. Front Range saves long taxis, waiting in line for departure , landing fees, & fuel expense. An inexpensive FBO shuttle ride of 15 minutes to Denver International is available if meeting a flight.
    Dallas Love, Palwaukee, Hawthorne for LAX, Haward for SFO, Peach Tree for Atlanta all can save time and money even if they aren’t the closest to town.
    Haven’t see this discussion anywhere.

  3. Gregory Tolmas
    Gregory Tolmas says:

    There was one short line about the ease of spoofing a receiver. I have had in the vicinity of Ridgecrest (KIYK) my track jump several miles. Since this location was more than a hundred miles from the nearest differential transmitter site I assume that the receiver tracker that I use defaulted to WAAS when in this area. The point being DON’T BET ON A SINGLE FUSE and and have plans B and C hot and ready. Its my assumption the the weapons station has developed and is testing systems to create locale disturbances of the system for vessel protection and if so so HINNEY will hack it and because of the nature of a Hinney play with it for self-gratification

  4. Don Rieser
    Don Rieser says:

    Another great article John. Compared to the “good old days”, I almost feel guilty flying GPS approaches with Foreflight and the approach plate on the map. Times have truly changed for the better and I hope we start to see some real improvement in the IFR safety statistics.

  5. Richard Gallaher
    Richard Gallaher says:

    I was an airport servielence radar tech and pilot in 1988 working at the Naval Air Test Center. I remember the push back I got when I recommended using auto transponders sending GPS position data because the data was more accurate when the aircraft was at an extended distance from the radar. The fear then was how easy it was to jam the weak GPS signal.
    It looks like 30 years later it will now be used…

  6. David Megginson
    David Megginson says:

    Great article, John—thanks. Last week I was reminded of how much we take GPS for granted when I was using my smartphone in the car (from the passenger seat) to find the best route out of downtown Montreal, when suddenly the 720 went into its long tunnel, and I lost signal. I have to admit to a moment of panic before I remembered “oh yeah, read the road signs.”

    We don’t fly through tunnels, but we do occasionally fly through areas of deliberate military GPS jamming tests and unplanned signal losses (I’ve experienced both), and if — deity forbid — there’s ever a drone-based 9/11-style attack on North American soil,the first response will probably be to scramble the GPS signals.

    How do we keep our VOR and NDB skills sharp when we’re not using them routinely any more? I wouldn’t want to turn back the clock to the bad old days, but I also think it shouldn’t end up being an emergency situation (like an engine failure or partial panel) on those rare occasions when the GPS signal vanishes.

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