Safeguarding Business Aviation for Upper C-Band Deployment

The Federal Communications Commission's planned 2027 auction of Upper C-Band spectrum (3.98–4.2 GHz) is generating significant regulatory and financial pressure across business aviation, as the frequencies sit immediately adjacent to the 4.2–4.4 GHz band where radio altimeters operate. These radar-based systems are not peripheral equipment — they provide absolute altitude data critical to instrument approaches, autoland systems, terrain awareness, and low-visibility operations. Out-of-band emissions from full-power terrestrial 5G base stations operating in the Upper C-Band can bleed into radio altimeter receivers, producing erroneous altitude readings that pose direct flight safety risks, particularly during the most demanding phases of flight below 2,500 feet AGL. The FAA's notice of proposed rulemaking, to which a broad coalition including NBAA, aviation manufacturers, and pilot groups submitted comments in March 2026, would mandate replacement of radio altimeter units across an estimated 40,900 aircraft and 58,600 individual RA units — a scope that encompasses essentially the entire IFR-capable fleet operating in U.S. airspace.

The financial exposure for operators is substantial and, according to industry stakeholders, likely underestimated by the FAA's own rulemaking analysis. The agency's NPRM pegged per-unit replacement cost at approximately $80,000, yielding a fleetwide estimate of $4.49 billion in undiscounted retrofit costs. Industry consultation with operators and manufacturers, however, places the realistic per-unit figure closer to $120,000 when equipment, certification, and labor are fully accounted for — a 50 percent variance that, applied at scale, could push total industry costs well above $7 billion. For Part 91 and Part 135 operators specifically, the burden is compounded by the absence of the revenue base that commercial airlines can use to absorb large avionics mandates. A large-cabin business jet operating under Part 91 may have two or more radio altimeter units, and the cost of replacement — combined with downtime, supplemental type certificate work, and maintenance coordination — represents a meaningful capital event for even well-resourced flight departments.

The regulatory framework for cost recovery is not without precedent, and that precedent is the central pillar of NBAA's current advocacy posture. When the FCC auctioned Lower C-Band spectrum (3.7–3.98 GHz) in 2020–2021, it imposed out-of-band emission limits and established a process under its "emerging technologies framework" through which incumbents compelled to modify equipment due to commission-initiated spectrum changes could seek reimbursement of reasonable, documented costs. NBAA and NATA submitted joint comments to the FCC in February 2026 demanding that the same framework be applied equitably to Part 91 and Part 135 operators in the Upper C-Band proceeding. The Lower C-Band experience also demonstrated that the interference concern was not theoretical — post-deployment analysis by RTCA and others identified insufficient protection margins even with the filters retrofitted on some existing altimeters, providing technical support for the position that Upper C-Band deployment without new-generation RA standards would create genuine operational hazards.

For working pilots and flight operations departments, the practical implications are multilayered. In the near term, operators should anticipate that radio altimeter replacement will become a mandated equipage item with a compliance deadline tied to the post-2027 Upper C-Band deployment timeline — similar in character, though potentially larger in cost, to the ADS-B mandate. Dispatch and airworthiness implications during the transition period deserve attention, particularly for operators conducting Category II/III approaches, offshore operations, or helicopter air ambulance flights where radio altimeter data is a go/no-go dependency. NBAA SVP Doug Carr's reference to the 5G C-Band experience as a template for stakeholder collaboration is significant: the 2021 process, while contentious, ultimately produced a phased deployment approach with defined aviation protection zones around certain airports. A similar outcome — phased spectrum rollout, defined OOBE limits, and reimbursement mechanisms — is the industry's stated objective for the Upper C-Band proceeding, though the final FCC rule and auction terms remain unresolved as of mid-2026.

The Upper C-Band issue reflects a structural tension in U.S. spectrum policy that aviation operators have encountered repeatedly as telecommunications infrastructure expands into frequency ranges adjacent to safety-critical avionics. The broader trend — congressional directives to monetize spectrum, FCC auction timelines driven by wireless industry demand, and aviation's role as an incumbent user of adjacent allocations — shows no sign of abating. Business aviation's relatively fragmented ownership structure, with nearly 14,000 individual owners and operators affected by the current NPRM, makes coordinated advocacy through organizations like NBAA essential to ensuring that the FAA and FCC rule with full awareness of operational and financial realities beyond the airline sector. The outcome of this proceeding will likely set terms and precedents that shape how aviation navigates future spectrum disputes, making NBAA's current engagement as much about long-term regulatory positioning as it is about any single avionics mandate.