Don't start celebrating just yet if you own a Boeing 747-8, 747-8F, 777

Nine out of ten of America's commercial aircraft can land in low visibility using radio altimeters at US airports that have nearby 5G C-band masts, the country's aviation watchdog said this week.

There is some concern that signals at the top of the 5G C-band, namely 3.98GHz, could bleed into the 4.2-4.4GHz band used by airliners' radio altimeters, which are quite handy when visibility is poor. The presence of 5G-C masts could thus affect the ability of aircraft to land safely in sub-optimal weather, it's been claimed.

AT&T and Verizon this month agreed to partially stall the roll out of 5G-C masts in the US – deploying the tech away from airports – while the Federal Aviation Administration (FAA) looked into matter. Specifically, the watchdog has been checking the radio altimeters on commercial aircraft to see if the equipment works as expected within range of 5G-C communications.

An estimated 90 per cent of the United States' commercial aircraft fleet has now been approved by the FAA to fly into airports using radio altimeters in low-visibility conditions if 5G-C cellular towers are nearby, up from 78 per cent last week. If 5G-C isn't present, there are no restrictions.

The approved list of aircraft-altimeter combinations includes all Boeing 717, 737, 747, 757, 767, 777, and 787 models; Airbus A300, A310, A319, A220, A320, A321, A330, A340, A350, and A380 airliners; MD-10/-11 models; Embraer 120, 170, and 190 regional jets; and all CL-600/CRJ regional jets.

That said, on Tuesday, the FAA ruled Boeing 747-8, 747-8F, and 777 aircraft aren't allowed to land at some airports due to what's described as "an additional hazard presented by 5G C-band interference."

"The FAA determined that anomalies due to 5G C-Band interference may affect multiple airplane systems using radio altimeter data, including the pitch control laws, including control laws that provide tail strike protection, regardless of the approach type or weather," the watchdog said [PDF].

"These anomalies may not be evident until very low altitudes."

This particular ruling affects an estimated 336 Boeing planes in the US, and 1,714 worldwide, the agency said. The directive "does not apply to landings at airports where the FAA determined the aircraft altimeters are safe and reliable in the 5G C-band environment. It also does not apply to airports where 5G isn't deployed."

Larger airports, such as New York's JFK and California's LAX and SFO, are not affected by any of this due to being 5G C-band-free zones. The Register has asked Boeing for comment. 

The US stands almost alone in its concerns of 5G-C and its potential harm to aviation systems. Europe and the UK have cleared flights for landing and takeoff. Japan has said interference isn't an issue so long as 5G-C base stations are kept 200 metres from approach paths. ®

https://www.theregister.com/2022/01/26/faa_5g_boeing/