AT&T is delaying the launch of 5G on its C-Band spectrum due to concerns about interference with flight cockpit safety systems, and Verizon will reportedly postpone its network activation as well.

“At the request of the Department of Transportation, today we have voluntarily agreed to defer Phase I C-Band deployments for one month to January 5”, AT&T told Mobile World Live in an emailed statement. The operator stated it is continuing to work with the US Federal Communications Commission (FCC) and with the Department of Transportation’s Federal Aviation Agency (FAA). The goal of the talks is to understand issues related to the co-existence of 5G and radar altimeters in the C-Band.

“It is critical that these discussions be informed by the science and the data”, AT&T stated. “That is the only path to enabling experts and engineers to assess whether any legitimate co-existence issues exist”.

The Wall Street Journal reported Verizon will also postpone its C-Band launch until 5 January 2022. According to that report, the FAA was planning to issue new guidelines for pilots which would have limited their use of some automated cockpit systems due to possible interference from 5G.

Verizon has invested $53 billion in C-Band, including funds spent to purchase the spectrum from the government and reimburse satellite operators for moving their equipment to other frequencies. In June the operator told analysts its C-Band spectrum would cover 90 million points-of-presence by the end of 2021.

AT&T spent $23.4 billion on C-Band licences, in addition to the cost of compensating the satellite operators for clearing the spectrum.