(NEXSTAR) – Federal officials have identified 50 U.S. airports that will have “buffer zones” when wireless companies turn on 5G service in a few weeks. The services will use frequencies in a radio spectrum called the C-band, which has caused concerns because it could impact flight operations.

After requests from both a major airline trade group — Airlines for America — and Transportation Secretary Pete Buttigieg and Stephen Dickson, head of the Federal Aviation Administration, AT&T and Verizon recently delayed rolling out the new 5G service.

Airlines for America told the Federal Communications Commission that using C-band 5G near dozens of airports could interfere with devices that measure an airplane’s height above the ground. Buttigieg and Dickson warned that without a delay, there would be an “unacceptable disruption” to aviation because flights would be canceled or diverted to other cities to avoid potential risks to air safety.

Friday, the Federal Aviation Administration released a list of 50 airports nationwide that will have buffer zones when 5G is rolled out by wireless carriers later this month. The buffer zones are intended to reduce the risk of airplane instruments like an altimeter, which measures the craft’s altitude, being affected by potential interference.

Altimeters are crucial to flights making low-visibility landings. According to the FAA, aircraft will be required to have an altimeter “that has been proven to be accurate and reliable in the U.S. 5G C-band environment.”

The list of airports that will have 5G buffer zones includes those in New York, Dallas, Chicago, San Francisco, Miami, and Las Vegas. Airports were selected based on traffic volume, the number of low-visibility days, and geographic location. These buffer zones will only protect the last 20 seconds of flight, according to the FAA.

Many airports are not currently affected by 5G. For those airports not on the list, the FAA says it does “not necessarily” mean low-visibility flights cannot occur. In some cases, like Denver International Airport, 5G is not yet being deployed. With others, the FAA says the 5G towers are far enough away to create a natural buffer.

Wireless carriers now plan to turn on the 5G C-band service on January 19.