Enlarge (credit: Getty Images | Daniel Garrido)

The Federal Aviation Administration will give airlines another year to fix or replace airplane altimeters that can't filter out cellular transmissions from outside their allotted frequencies. In a notice of proposed rulemaking (NPRM) released today, the FAA proposed a deadline of February 1, 2024, to replace or retrofit faulty altimeters, which are used by airplanes to measure altitude.

Out of 7,993 airplanes on the US registry, the FAA said it "estimates that approximately 180 airplanes would require radio altimeter replacement and 820 airplanes would require addition of radio altimeter filters to comply with the proposed modification requirement." The total estimated cost of compliance is $26 million.

The requirement could finally end a dispute between the aviation and wireless industries, which has prevented AT&T and Verizon from fully deploying 5G on the C-Band spectrum licenses the wireless carriers purchased for a combined $69 billion . Airplane altimeters rely on a spectrum from 4.2 GHz to 4.4 GHz, but some cannot filter out 5G transmissions from the carriers' spectrum in the 3.7-3.98 GHz range.

Enlarge / Airbus 320 cockpit. (credit: Getty Images | Skyhobo )

The Federal Aviation Administration says it finally has a plan for the industry to replace or retrofit airplane altimeters that can't filter out transmissions from outside their allotted frequencies. The altimeter problem has prevented AT&T and Verizon from fully deploying 5G on the C-Band spectrum licenses the wireless carriers purchased for a combined $69 billion .

The FAA was urging airlines to retrofit or replace altimeters in recent months and now says it has finalized a plan. An FAA statement on Friday said that "airlines and other operators of aircraft equipped with the affected radio altimeters must install filters or other enhancements as soon as possible."

AT&T and Verizon said they will be able to accelerate 5G deployments near airports in the coming months, but the carriers agreed to continue some level of "voluntary mitigations" in the airport areas until July 2023.

Enlarge (credit: Getty Images | BackyardProduction)

The Federal Aviation Administration is reportedly urging airlines to retrofit or replace altimeters that receive transmissions from outside their allotted frequencies. The FAA is meeting Wednesday "with telecom and airline industry officials on a push to retrofit and ultimately replace some airplane radio altimeters that could face interference from C-Band 5G wireless service," Reuters reported Tuesday .

The Reuters report continued:

The FAA wants to use the meeting to establish "an achievable timeframe to retrofit/replace radar altimeters in the US fleet," according to a previously unreported letter from the FAA's top aviation safety official Chris Rocheleau reviewed by Reuters. It also asked aviation representatives "to offer options and commit to actions necessary to meet these objectives."

Some altimeters used by airplanes to measure altitude apparently cannot filter out transmissions from C-Band frequencies assigned to wireless carriers for 5G. Altimeters are supposed to use frequencies from 4.2 GHz to 4.4 GHz, while wireless carriers' C-Band licenses are for 3.7 to 3.98 GHz.