FAA Proposes $4.5B Radio Altimeter Upgrade Mandate for Airlines

The US Federal Aviation Administration (FAA) has formally proposed new regulations that would compel airlines to upgrade aircraft radio altimeters for the second time in three years. This regulatory action stems from the Consolidated Appropriations Act of 2025 signed into law by the Trump administration, which directs the Federal Communications Commission (FCC) to auction 100-180 MHz of spectrum in the 3.98-4.2 GHz range (Upper C-band) for wireless services.

Radio altimeters operate in the adjacent 4.2-4.4 GHz band and provide critical altitude data to flight systems. The FAA's notice of proposed rulemaking (NPRM) states that existing altimeters upgraded under 2023 airworthiness directives cannot withstand interference from anticipated Upper C-band wireless operations. The agency explicitly warns that voluntary mitigation measures near airports will sunset in 2028 without guaranteed extensions.

Compliance requirements mandate that new altimeters must:

1. Demonstrate immunity to interference from adjacent-band wireless transmissions
2. Maintain altitude measurement accuracy during exposure to C-band signals
3. Integrate with aircraft safety systems without degradation of performance

The FAA estimates retrofitting the entire US commercial fleet will cost $4.49 billion, with annualized expenses of $424 million when calculated at a 7% discount rate over 20 years. Airlines must complete upgrades by the FCC's authorization date for Upper C-band services, projected between 2029 and 2032. This deadline aligns with when wireless providers gain full operational rights in the spectrum.

This marks the second major altimeter overhaul since 2023, when carriers spent approximately $637 million upgrading equipment to address 5G interference concerns in the Lower C-band. The FAA acknowledges that manufacturers have been developing next-generation altimeter standards since 2021, but notes the new technical requirements exceed previous specifications.

The proposed rule is open for public comment until March 9, 2026. Airlines should immediately review NPRM docket FAA-2026-XXXX and assess fleet retrofit requirements against the projected compliance timeline.