Airlines warn risks from 5G are too big to ignore, but is it all hot air?


By Sandra Stafford September 5, 2021 9:00AM

The mobile wireless industry is preparing to deploy 5G all across the country, and 6G is already in development — but millions of people in the United States don’t even have access to household internet.

This differential in access is called the “digital divide,” and the Federal Communications Commission (FCC) is trying to bridge it.

Part of its plan is to let mobile wireless companies use broadcast spectrum in the 3.7-3.98 GHz band, commonly referred to as “C-band.” With a license to use C-band, wireless companies can provide 5G service through relatively small base stations. This would make it easier to bring 5G to rural areas, where providing internet through fiber requires vast, expensive infrastructure for relatively few customers. Verizon, AT&T, and T-Mobile spent over $80 billion at auction to get these C-band licenses.

The FCC formally issued the policy changes in March 2020. The report and order (R&O) was the result of nearly three years of consideration, during which members of the public were invited to comment on the matter. There was a wide range of interested parties, from NPR to the Mormon Church, but aviation industry groups have been among the most involved.

Aviation industry speaks up

The aviation industry’s concerns revolve around a piece of equipment called a radar altimeter (or radio altimeter). The radar altimeter is used by all kinds of aircraft to measure altitude, the distance between the aircraft and the ground. It works by transmitting a signal toward the ground, then determining altitude based on the time it takes the signal to reflect off the ground and back to the aircraft.


These 5G sources can also create “spurious emissions.” These are unwanted signals in the 4.2-4.4 GHz band. Since these signals are within the same bandwidth radar altimeters are supposed to receive, they can’t be filtered out. The radar altimeter has no way to tell them apart from the returning signal, so it may determine altitude incorrectly.

The weaker signal gets washed out by the stronger one.

A false altitude report is a serious error that can cause several other systems to respond inappropriately. Radar altimeters operate through the entire flight, and the data isn’t just displayed to the pilot. Altitude data feeds into important systems, like the Traffic Collision Avoidance System and Automatic Dependent Surveillance-Broadcast System, which monitors the airspace to prevent midair collisions. In October 2020, the RTCA Report shed some light on the danger of false altitude reports during landing.

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