Clash of Aircraft altimeter frequency with 5G frequency
In a notice of proposed rulemaking (NPRM) released today, the Federal Aviation Administration (FAA) has given airlines another year to replace or repair faulty airplane altimeters that can’t block cellular transmissions from outside their allotted frequencies.
A February 1, 2024 deadline has been proposed to replace or retrofit faulty altimeters used by aircrafts to measure altitude. The FAA estimates that approximately 180 airplanes would need radio altimeter replacement and 820 airplanes would need the addition of radio altimeter filters to meet the proposed modification requirement, out of 7,993 airplanes on the US registry.
The total estimated cost of compliance is $26 million. A dispute between the aviation and wireless industries that had prevented AT&T and Verizon from fully deploying 5G on the C-Band spectrum licenses the wireless carriers purchased for $69 billion is now finally over.
Airplane altimeters work on frequencies from 4.2 GHz to 4.4 GHz, but some can’t use carriers’ spectrum in the 3.7–3.98 GHz range to filter out 5G transmissions. “Some radio altimeters may already demonstrate tolerance to 5G C-Band emissions without modification, while others may need to install filters between the radio altimeter and the antenna to increase their tolerance.”
For other aircraft, the addition of a filter will not be sufficient to mask interference susceptibility; therefore, the radio altimeter will need to be replaced with an upgraded radio altimeter.
The FAA believes erroneous system warnings due to a malfunctioning radio altimeter will lead to flight crews becoming desensitized to warnings.
“As soon as possible, the FAA had directed airlines to replace faulty altimeters or retrofit them.”,, But the notice that was issued today said February 1, 2024, “is the date the FAA determined to be as soon as reasonably practicable, consistent with FAA policy.”
The FAA will accept public comment on its new proposal for 30 days before finalizing it.
According to the lobby group Airlines for America, airlines are “working hard to ensure their fleets are equipped with compliant radio altimeters, but global supply chains continue to lag behind current demand; any government deadline must take this into account.”
The proposed rule would affect aircraft that are issued Part 121 certificates for carriers offering scheduled air service, which typically include “large, US-based airlines, regional air carriers, and all cargo operators”, the FAA says.
The notice stated that “to limit the number of erroneous system messages and the unsafe conditions they create, the FAA proposes to require that all airplanes operating under Part 121 meet the PSD performance curve to be allowed to operate in the United States after February 1, 2024”. , Because of the 220 MHz guard band between 5G and altimeter operations and power limits the FCC required for C-Band transmissions, the FCC concluded that harmful interference to altimeters was unlikely “under reasonable scenarios.”
