The FAA published formal notices to pilots on Thursday, instructing them not to perform low-visibility landings where new 5G capabilities are deployed.
The notices will apply to aircraft equipped with radio altimeters that have either proven not to be reliable within areas to be impacted by new 5G transmissions or that have not yet been tested for such reliability.
Altimeters, which are used to measure a plane's distance from the ground when flying at altitudes of approximately 2,500 feet and below, are especially important during approaches and landings in bad weather conditions.
Notices were issued Thursday for approximately 100 airports with passenger service, according to the Air Line Pilots Association (ALPA) union. They will take effect on Jan. 19, when AT&T and Verizon begin 5G transmissions in 46 markets using the C-Band Spectrum, which encompasses a frequency range that is closer to frequencies used by aircraft than has previously been allowed in the U.S.
Numerous major airports are subject to 5G-related NOTAMs, including Los Angeles International, Charlotte, Boston, Newark, JFK, New York LaGuardia, Dallas Fort/Worth, Houston Bush Intercontinental, Houston Hobby, Chicago O'Hare, Chicago Midway, Phoenix Sky Harbor, Philadelphia, Minneapolis-St. Paul, Seattle, Orlando and Miami.
In a Thursday statement, the FAA said it is using testing results from manufacturers and data provided by wireless companies to determine which types of aircraft altimeters will perform reliably in areas impacted by 5G.
"The FAA expects to provide updates soon about the estimated percentage of commercial aircraft equipped with altimeters that can operate reliably and accurately in the 5G C-Band environment," the agency said. "The aircraft with untested altimeters or that need retrofitting or replacement will be unable to perform low-visibility landings where 5G is deployed."
ALPA said the landing restrictions will ensure that pilots maintain a high level of safety as 5G deployment begins, but ALPA added that they'll severely impact operations across the entire U.S. aviation system.