5G and Altimeters: The Problem With Interference

    Have you ever wondered exactly how an aircrew tells how far they are above the ground? While most higher altitude readings use air pressure differences, low altitude devices designed in the 1920s set up a showdown between 5G and altimeters.

    The vast majority of air traffic time is spent at high altitude. From multiple redundant alitmeters systems to GPS positioning, both the crew and the aircraft know where the ground is. But it’s still just an approximation; the math is pretty good, but it’s not perfect.

    The Closer to the Ground, The More Impotant the Altimeters

    When operating close in to the ground, aircraft have relied on a device called a radar altimeter for decades. The radar altimeter works by bouncing energy directly off of whatever is below the aircraft. The return timing tells the crew exactly where the ground is; no approximations of position and onboard terrain elevation data required.

    This device, in concert with barometric altimeters, give pilots the ability to fly with pretty incredible precision. So what’s the problem? The video you can’t stand to skip, the crystal clear call clarity, the massive bandwidth of 5G; they all throw aircraft landings into question.

    5G services operate in the C band, from around 3.7 to 3.98 Ghz. This happens to also be directly in the middle of where radar altimeters operate. But who cares, it’s only one instrument, right?

    Training vs Systems in Aviation and 5G Operations

    If it’s obviously wrong, then the crew can disregard it, if they happen to notice. But modern radar altimeters feed a whole host of other systems, like terrain avoidance systems, traffic collision avoidance, even the large integrated networks that controllers use to monitor and route air traffic. A simple problem quickly becomes more complex.

    The scariest issue for this interference comes not from massively wrong readings, but subtle ones. Even the most experienced crew might not notice that the radar altimeter is a few tens of feet off. For systems like auto-landing and minimum-visibility weather operations, this could be disastrous. It doesn’t take much of an error to hit the ground before you’re ready. The erroneous radar altimeter might cause hard landings, or worse, full-scale crashes. It’s up to the crews to keep their passengers safe.

    The ongoing regulatory battle between 5G and altimeters that use the same spectrum will be interesting to watch. The future of aerospace is often dictated by things we can’t see, and the electromagnetic spectrum is no exception. So what do you think? Will we see a rollback of 5G service near airports, or will we force the aviation industry to adapt and overcome?


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