Upper C-Band Flexible Use (3.98–4.2 GHz)

Current understanding

The FCC is reallocating 160 MHz of Upper C-band spectrum (3.98–4.2 GHz) for terrestrial flexible wireless use through an auction scheduled by July 2027, extending the framework previously used for the Lower C-band. New licensees must fund the migration of incumbent Fixed Satellite Service (FSS) operations and provide rebates to aircraft operators for radio-altimeter retrofits, a mechanism intended to preserve aviation coexistence given the adjacency to the 4.2–4.4 GHz radio-altimeter band.

Evidence log

• 2026-10-08 — Airworthiness Directives; Various Helicopters: 2026 — Helicopter AD prohibiting certain radio-altimeter-dependent operations in Canadian airspace illustrates that 5G C-band deployments outside U.S. jurisdiction continue to generate altimeter-interference mitigations through FAA airworthiness action. (novelty: 2)
• 2026-07-31 — Requirements for Interference-Tolerant Radio Altimeter Systems: 2026 — FAA final rule imposes new interference-tolerance performance standards on radio altimeters with phased 2030/2034 deadlines aligned to FCC Upper C-band spectrum authorization, forming the aviation-side complement to the FCC’s licensee-funded altimeter retrofit rebates. (novelty: 3)

Open questions

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