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FAA sets 2024 deadline for preventing 5G crash landings

US watchdog puts its foot down: Even a small possibility of interference means a fix is mandatory

America's Federal Aviation Administration is directing all aircraft to get new altimeters, or install filters on existing ones, by February 1, 2024, to eliminate risks posed by C-band 5G networks.

Under the new rule, passenger and cargo aircraft will not only be required to address altimeter concerns by the year after next, but airlines will also have to update flight manuals to prohibit low-visibility landings (which radio altimeters are used extensively in) after June 30, 2023, unless they have been retrofitted.

The order [PDF] could bring an end to years of back-and-forth discussions between the FAA and telecommunications operators, which have tried to address the issue since the FAA warned in late 2021 of service delays and interruptions if C-band networks were switched on in January 2022, as was initially planned. 

The C-band, which occupies frequencies between 3.7-3.98GHz, is near to the 4.2-4.4GHz spread used by radio altimeters, posing a potential problem if cell signals manage to bleed over into aircraft bands.

By January of last year the FAA said it had cleared 90 percent of the commercial aircraft flown in the US to land at airports with nearby C-band towers, but Boeing 747-8, 747-8F and 777 aircraft were excluded, and the 737 was later added to the list as well.

Fast forward to May, the FAA had decreed that airline operators would be forced to replace vulnerable altimeters or install filters, a decision that it carried over to the newly proposed rule.

Months later in June, Verizon and AT&T agreed to slow C-band rollouts near airports, an agreement that will end in July of this year and clear the way for more C-band deployments.

Shut up and install the filters

The FAA's laborious discussion and investigation into the realities of the risk posed by C-band 5G signals has been called excessive by some given the extent of the fix in other nations. 

Japanese scientists who studied the issue, for example, said the issue could be resolved by not deploying high-power 5G masts within 200 meters of aircraft approach routes. The FAA, however, takes its job very seriously.

"We rely on data to mitigate risk, and never assume that a piece of equipment or a given flight scenario is safe until this can be demonstrated. If there's the possibility of a risk to the flying public, we are obligated to restrict the relevant flight activity until we can prove it is safe," the FAA said.

During the couple of years that the C-band issue has been on the FAA's radar, the agency said it had received over 420 reports of radio altimeter anomalies occurring within known C-band deployment zones. 

While most of the reports were attributable to other causes, the FAA said in around 100 of the incidents it "could not rule out 5G C-Band interference as the potential source of the radio altimeter anomalies." The FAA said the incidents all involved flight deck effects, like false terrain awareness traffic collision warnings, incorrect radio altimeter data and more. 

The FAA admits those issues may seem "minor in isolation," but that they have serious implications over time, especially as C-band deployments near airports begin in earnest in the second half of 2023. 

The agency is concerned that repeated false warnings, which it believes "will occur more frequently as telecommunication companies continue to deploy 5G C-Band services," will desensitize flight crew to actual emergencies.

In other words, better safe than sorry, so pipe down and install those new altimeters. 

The FAA estimates 7,993 aircraft will need to have flight manual revisions made, while 180 aircraft will require a total altimeter replacement. An additional 820 aircraft will need a C-band filter added.

Airlines for America, a trade group that represents several US air carriers, said of the proposal that "carriers are working diligently to ensure fleets are equipped with compliant radio altimeters, but global supply chains continue to lag behind current demand."

While it didn't express frustration with the FAA's 2024 deadline, Airlines for America did appear to at least consider it a bit tight given supply chain concerns. "Any government deadline must consider this reality," the trade group added. ®

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