The trade association and lobby group Airlines for America (A4A), which represents American Airlines, Delta Air Lines, United Airlines and others, also requested that the FAA modify a proposed 5G security directive “to reflect technical realities and the continued safe operation of many aircraft.” The association issued a warning that without changes, the “material number of aircraft” in US fleets would not change until July, which may “severely limit operations” and result in flight delays and cancellations.

The FAA proposed in January that by February 2024, all passenger and cargo aircraft operating in the United States must be equipped with 5G C-band-tolerant radio altimeters or certified filters. The organization reaffirmed on Friday that it would consider all objections.

Concerns that 5G service could interfere with in-flight altimeters, which provide data on a plane’s altitude and are critical for landing in bad weather, led to disruptions at some US airports last year, involving international carriers.

Additionally on Friday, a coalition including Boeing, Airbus, Lockheed Martin, Raytheon, pilot unions, and airlines complained the directive “does not provide sufficiently robust controls to ensure safety as both aviation operations and wireless services co-evolve” and lacks a reasonable cost estimate.

In June, Verizon Communications and AT&T voluntarily agreed to postpone the usage of some C-band 5G until July while the aviation industry works to retrofit planes to prevent interference.

Mobile network operators invested more than $80 billion in the C-band 5G spectrum, including Verizon’s $52.9 billion in auction and clearing costs.

The wireless trade group CTIA, which represents Verizon and AT&T, argue that the FAA has given the airlines enough time and should not extend the deadlines.

“By requiring accountability, the FAA is taking important steps to ensure radio altimeter performance is more resilient while enabling timely C-Band 5G deployment,” CTIA representatives said.

The FAA’s $26 million estimate is considerably too low, according to the International Air Transport Association (IATA), which forecasts expenses of at least $637 million and cautions that many airlines run the risk of missing deadlines.