If you’re reading much aviation news, January 19 promises to be a disaster. According to airline executives and trade groups, 5G data service being turned on near airports will lead to a disaster—words like “significant disruptions” are being tossed around left and right. And AT&T and Verizon, the two companies that had gotten the FCC okay to launch 5G service today, separately announced they were voluntarily putting off flipping the on switch on some of their 5G towers, though it’s not clear what either company’s future plans will be. The towers in question, according to reports, are near busier commercial airports.
Those of us who embrace a few wrinkles in the mirror image every morning will recall a similar feeling of impending doom, a little more than two decades ago, as we prepared to bid the 20th century goodbye. A lot of very intelligent people feared that computers wouldn’t click over to the proper year format when we rolled into the year 2,000 and any device with a computer chip seemed primed to wreck human civilization. Luckily, by the time the ball dropped in Times Square, critical systems had been updated, and the lights stayed on.
So, what’s the conflict between 5G data networks and aviation? Radar altimeters are the sticking point. They utilize the 4.2-4.4 GHz band to determine an aircraft’s exact height above the ground by bouncing a radar beam off the ground. That’s not a common setup on most general aviation airplanes, but on aircraft capable of flying in very challenging weather, namely bizjets and airliners, it is a critical system. For landing in weather lower than a standard ILS (minimum weather requirement of 200 foot ceiling and ½-mile visibility), radar altimeters are required.
Here’s why. When an aircraft is flying an RNAV RNP or Category II/III ILS approach, the time from seeing runway lights until touchdown can be just a brief moment, so knowing your exact height as you come down the approach is paramount. Instead of the standard half-mile visibility, operators with special authorization can operate to visibility that’s a fraction of that in the case of the CAT III ILS approaches.
Radar altimeters are also a critical component of Ground Proximity Warning Systems, which provide advance warning of rising terrain. Their adoption 25 years ago helped make controlled flight into terrain (CFIT) accidents, largely a historical footnote.
The 5G network rolling out this week operates on two sets of frequency bands. The lower frequency band ranges from 450 MHz to 6 GHz, which is the conflict with aircraft radar altimeters. The potential exists for interference—and on December 31, 2021, FAA Administrator Steven Dixon and Transportation Secretary Pete Buttigieg asked for a delay in 5G rollout to assess the potential for interference. That delay will expire January 19.
Airports with approaches affected by 5G signals will have NOTAMS issued to inform pilots that approaches requiring radar altimeters will not be available except for aircraft incorporating an alternate method of compliance with Airworthiness Directive 2021-23-12 and 2121-23-13. So far, about 1,500 such NOTAMS have been issued—adding to the jumble of information presented to many professional pilots before each flight. Picking a random flight to sample—Atlanta to New York’s JFK airport—showed 66 NOTAMs, spreading across six 8.5×11″ sheets of paper. The NOTAM for JFK’s 5G-limited approaches was the 39th one, on page four. Many in the industry have long joked that if you want to keep a secret from a pilot, printing it as a NOTAM is the way to go, and burying these NOTAMS like that is a great way to spring a gotcha on pilots who scan their flight plans with anything less than a meticulous reading of every line of text.
Will 5G really affect the aviation industry? Probably, although the ultimate impact will likely be less than we’re being led to believe. Many professional pilots fly no more than a handful of approaches that absolutely require a radar altimeter in a given year. On normal weather days, the impact should be manageable, but until aircraft are demonstrated to operate without interference or alternative methods of compliance are implemented, we’ll likely see weather delays amplified. For the average general aviation pilot, even those who use their instrument flying skills on a regular basis, the impact should be almost nonexistent.
