How Do Airliners navigate (article)

John from PA

Clear and accessible

Provides an easy to digest overview of present day navigation systems, written by an Airbus A320 pilot.

Thank you for sharing.

Interesting, another reason

Interesting, another reason I don't think failure of one system doomed the Malaysian flight a few years ago.

John B - Garmin 765T

Different strengths

GPS and the inertial method have nicely complementary flaws and strengths.

Once aligned and with initial position known, the inertial system does not need anything but power to continue providing position and velocity. So it does not care about jamming, antenna failures, and the host of other things that can temporarily interrupt the provision of data of pretty much all the other systems, from GPS to VOR.

But inertial is subject to drift. And even a very good inertial system can build up miles of position error in a few hours, which is still splendidly better than good old-fashioned dead reckoning, but way worse than almost anything else.

GPS, on the other hand, is subject to outages. Something can block the path from satellite to antenna. A bad actor can deliberately transmit powerful signal on GPS frequencies able to swamp receivers without sufficient antenna gain or pointed the wrong way. This is not just hypothetical. Famously the Kremlin in Moscow (there are other Kremlins) for years has been surrounded by an area in which most GPS receivers cannot get a fix. The eastern Med often has regions of poor GPS reception, as recently have Ukraine, Kaliningrad.

But good GPS receivers can pretty generally figure out whether they are getting a good fix (it takes vastly more clever engineering to spoof them than to jam them). So a mixed system can update the drifting inertial position to truth whenever the GPS solution is good, and use the inertial to interpolate, for minutes at a time if need be, and still get a quite wonderful overall solution.

Tesla has said it will be working toward more of a mixed system, using accelerometers already in the cars, in order to give better navigation inside parking garages and tunnels. I wish Garmin would do that.

personal GPS user since 1992