The airport 5G problem – where some planes with older or faulty radio altimeters could be confused by strong 5G signals – has resulted in a further compromise.
Carriers wanted airlines to have to promptly bring their equipment up-to-date, while an aviation body wanted the current restrictions to be made permanent …
Airport 5G problem
If you’re not familiar with the background, it’s a rather bizarre story of an embarrassing clash between two different government agencies.
Widespread adoption of cable and fiber-based TV services saw the effective demise of satellite TV. That meant that the frequencies previously used for those broadcasts could be freed-up for alternative use.
The usage of radio frequencies is controlled by the Federal Communications Commission (FCC), which decided that the frequencies were suitable for 5G use, and auctioned off the rights to use them. Verizon and AT&T jointly spent $68M on acquiring the rights to what was then labeled 5G C-band.
Another government agency, the Federal Aviation Administration (FAA), appeared to discover this fact after the event. It said that there was a risk of 5G C-band spectrum interfering with radio altimeters.
Radio altimeters on board airliners and some other aircraft bounce a radio signal off the ground and time the return signal to determine the altitude of the plane. This is much more accurate than pressure-based altimeters, and is used during the final approach and landing. It plays an especially important role in conditions of poor visibility.
The FAA had been voicing concerns about the potential risks of C-band interference since 2015, but it seems that the agency didn’t directly communicate these to the FCC until very late in the day.
The result was a very public and embarrassing argument between the two. It did seem clear that only older radio altimeters were at risk, and there was limited evidence even for these. After a series of proposed delays and compromises, an it appeared a deal had been done.
This imposed temporary 5G C-band restrictions at around 50 major airports, and gave the aviation industry until July 2023 to check their older aircraft, updating radio altimeters as required.
Deadline pushed back to February 2024
What everyone thought was the final deal turned out not to be.
Back in October, the aviation industry argued that the temporary restrictions weren’t doing anyone any harm, and the costs of fixing the issue was expensive, so why not just make the power limitations permanent?
However, the FAA has rejected this, instead giving airlines more time. Arstechnica reports.
Today, the FAA proposed a deadline of February 1, 2024, to replace or retrofit faulty altimeters, which are used by airplanes to measure altitude.
Out of 7,993 airplanes on the US registry, the FAA said it “estimates that approximately 180 airplanes would require radio altimeter replacement and 820 airplanes would require the addition of radio altimeter filters to comply with the proposed modification requirement.” The total estimated cost of compliance is $26 million […]
“Some radio altimeters may already demonstrate tolerance to the 5G C-Band emissions without modification,” the FAA said. “Some may need to install filters between the radio altimeter and antenna to increase a radio altimeter’s tolerance. For others, the addition of a filter will not be sufficient to address interference susceptibility; therefore, the radio altimeter will need to be replaced with an upgraded radio altimeter.”
One further option has been ruled out by the aviation regulator. Some had suggested that since the problem was only that affected radio altimeters reported a fault, but still functioned properly, could pilots simply be advised not to be concerned by the alerts at known problem spots?
The FAA rejected this, stating that this risked air crews becoming desensitized to system warnings, which “can lead to a catastrophic event.”
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