FAA Gives Airlines More Time to Fix 5G Interference Problem Affecting Approx. 1000 Planes

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.

“Some radio altimeters may already demonstrate tolerance to the 5G C-Band emissions without modification,” the FAA said. “Some may need to install filters between the radio altimeter and antenna to increase a radio altimeter’s tolerance. For others, the addition of a filter will not be sufficient to address interference susceptibility; therefore, the radio altimeter will need to be replaced with an upgraded radio altimeter.”

“Erroneous system warnings” pose a problem

The FAA said it “expects erroneous system warnings due to a malfunctioning radio altimeter to lead to flight crew becoming desensitized to system warnings. Such desensitization negates the safety benefits of the warning itself and can lead to a catastrophic event.”

The FAA had said in June 2022 that airlines must replace or retrofit faulty altimeters “as soon as possible.” But the notice issued today said February 1, 2024, “is the date the FAA has determined to be as soon as reasonably practical, consistent with FAA policy.”

The FAA will take public comment on its new proposal for 30 days before finalizing it. A Bloomberg report quoted lobby group Airlines for America as saying that airlines “are working diligently to ensure ﬂeets are equipped with compliant radio altimeters, but global supply chains continue to lag behind current demand. Any government deadline must consider this reality.”

The proposed rule would affect airplanes operating under Part 121 certificates. Those certificates are for carriers with scheduled air service, which generally includes “large, US-based airlines, regional air carriers, and all cargo operators,” the FAA says.