Aviation community worries about possible effects of 5G in C-band

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Radio altimeters provide critical operating altitude measurements for navigation, particularly at night or during band weather when visibility is poor. (Pixabay)

While the FCC contemplates changes to the 3.7-4.2 GHz band, aviation officials want to make sure it doesn’t disrupt aviation systems operating right next door in the 4.2-4.4 GHz band.

Representatives from the Aerospace Industries Association, General Aviation Manufacturers Association, Aviation Spectrum Resource, Lockheed Martin, the Airline Pilots Association, the Helicopter Association International, Garmin, Collins Aerospace and the International Air Transport Association recently met with FCC staff to discuss their concerns.

The groups are worried about potential harmful interference to aviation systems operating in the 4.2-4.4 GHz band, which is next to the 3.7-4.2 GHz band, also known as the C-band. Radio altimeter and wireless avionics intra-communications (WAIC) systems operate in the 4.2-4.4 GHz band, and “the uncompromised operation of both systems is essential to safety of flight,” the groups said in an ex parte filing (PDF).

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The concerns are not new—they’ve been voiced in previous filings (PDF)—but they illustrate yet another complicated issue for the FCC to consider as it contemplates ways to make C-band spectrum available for 5G terrestrial uses. Satellite companies use the band to deliver services to the likes of NPR, Comcast, Disney, CBS and other broadcasters.

The C-Band Alliance, which is comprised of the four main satellite companies that deliver these services, has said it can offer up to 200 megahertz (of the 500 megahertz in the band) through a secondary market sales process. Wireless carriers and their vendors say what they really need is 100 megahertz per operator to make it worthwhile.

RELATED: T-Mobile doubles down on its proposal for 3.7-4.2 GHz band

But as Boeing (PDF) and others point out, numerous other important industries depend on C-band satellite services as well, including for air traffic control and to distribute detailed weather information used to support flight operations.

According to Aviation Spectrum Resources (ASR), radio altimeters are especially vital for helicopters, which have a variety of missions often involving operation at lower altitudes, over uneven terrain, and in a variety of environments. Radio altimeters are recognized for having significantly improved aviation safety since their widespread implementation began in the 1970s.

Boeing has noted (PDF) that radio altimeters use relatively low power levels and must operate across the entire 4200-4400 MHz bandwidth to generate accurate results for landing aircraft.

“This need creates the risk that terrestrial radio transmitters operating near the upper edge of the C-band could overpower relatively weak reflected radio altimeter signals leading to false readings of an aircraft’s altitude above terrain,” ASR told the commission in a Dec. 11 filing (PDF).

Some members of the aviation industry are already working to test the potential impact of 5G signals to radio altimeter operations. Once that testing is complete, that data could be used to inform the commission before it makes any final decisions. Those tests were expected to be done before the end of the year, but were not complete as of the meeting that took place last week.

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