The FCC has been tasked by Congress to find and auction 800 megahertz of mid-range spectrum. This was a key element of the One Big Beautiful Bill that planned to use the proceeds from spectrum auctions to offset other costs created by the bill. The bill specifically requires the FCC to auction 100 megahertz of spectrum in the upper C-Band, located at 3.98 – 4.2 GHz.

The new requirement to auction that spectrum has resulted in a strong response from the aviation industry and the Federal Aviation Administration (FAA). This new controversy is a perfect example of the challenges the FCC is going to face as it tries to free up 800 megahertz of spectrum. Proposing to change any mid-range spectrum is going to rile up controversy and opposition from those who care about a given spectrum band.

In this case, the FAA’s concern is about interference. Apparently, they don’t want to take any chance of interference from cellular companies that would negatively affect airline altimeters. I think anybody who flies is on the FAA’s side – if they are concerned, I am concerned.

The FAA released new altimeter standards in 2023 that required changes to altimeters to be able to ignore any interference from the lower C-Band spectrum located at 3.7-3.98 GHz. Even though there is a gap between the lower C-band and the 4.2-4.4 GHz band that is used for altimeters, the FCC was worried about interference.

The FAA immediately reacted when Congress directed the FCC to auction off the 3.98 – 4.2 GHz band that sits directly adjacent to the altimeter spectrum. The FAA recognizes the reality that there are radios that don’t do a great job of fitting precisely in the spectrum band they are supposed to use.

The FAA warns that existing altimeters, including those that were retrofitted to meet the 2023 changes, are not going to be able to filter out interference from the upper C-Band spectrum. The FAA tracks reports of interference, and by the summer of 2025, it had received 659 reports of potential C-band interference. After analyzing the reports, the FAA identified 118 events that were directly attributable to lower C-band interference, and this was for spectrum that is not directly adjacent to the altimeter spectrum bands.

The FCC has a major dilemma since Congress specifically ordered the upper C-band spectrum to be auctioned. I’m not sure how the agency can resolve this other than by getting Congress to change the directive. The FCC could spend a lot of money to move altimeters to a different spectrum band, but there aren’t any convenient bands that meet the criteria. This would likely require the FCC to fund new altimeters.

Other wireless users are already starting to lobby to leave certain bands of spectrum alone as the FCC searches for 800 MHz of mid-range spectrum. Rural WISPs and others are already heavily lobbying for the FCC to leave CBRS spectrum alone, which is currently being used for rural broadband. The really big fight is going to come if the FCC wants to take any portion of the unlicensed 6 GHz spectrum that is being used for WiFi 7. The military had originally said it would go along with some changes in the mid-range spectrum bands, but already seems to be retracting from that commitment.

I don’t envy the FCC’s job of auctioning the spectrum as directed by Congress. I predict big lobbying battles and probably big lawsuits before much spectrum actually makes it to an auction.