FAA's Proposed Upper C-Band Radar Altimeter Performance Standards
FreeFlight Systems supports the FAA’s effort to formally define minimum interference‑tolerance performance criteria for radio altimeters to ensure continued safe operation as the RF environment evolves.
FreeFlight is actively engaged in industry coordination associated with this New Proposed Rule Making (NPRM). Behlul Poonawalla, Vice President of Products and Services, Programs and Contracts , is an active member of the relevant industry workgroup and is directly involved in monitoring technical discussions, proposed test criteria, and regulatory developments related to the NPRM.
Proposal Details and Terrain Series Compliance Approach
Applicability of NPRM FR Doc 2026‑00051 (FAA docket 2025-5666) and Advisory Circular AC 20-199
The NPRM proposes new, explicitly defined performance requirements for radio altimeters to demonstrate tolerance to out‑of‑band interference extending up to 4.2GHz, which represents an expansion beyond previously commercialized C‑band wireless operations. In addition the NPRM also proposes Radar Altimeter tolerance to a broader range of frequencies namely 4.4GHz to 5.6GHz.
The proposed rule introduces:
- New minimum interference‑tolerance performance thresholds
- FAA‑defined test conditions and pass/fail criteria
- Implementation timelines tied to aircraft operational categories
At the time of this response, these performance criteria and test methods remain under FAA rulemaking and have not yet been finalized.
Evaluation Status of FreeFlight Systems Radio Altimeters
With respect to the RA‑4500 MK II, RA‑5500, and RA‑6500:
- These products have not yet been formally evaluated against the specific performance criteria and test protocols proposed in NPRM FR Doc 2026‑00051 (FAA Docket 2025-5666), because those criteria are not final.
- FreeFlight Systems is currently performing a detailed technical review of the NPRM to assess any additional qualification testing, documentation, or compliance activities that may be required once the final rule is issued.
- FreeFlight’s evaluation and compliance planning will be conducted in accordance with the finalized FAA requirements and accepted test procedures.
Planned Compliance Approach and Evidence
Upon issuance of the FAA’s final rule and associated test guidance, FreeFlight Systems anticipates providing, as applicable:
- Documented compliance test evidence addressing the finalized Upper C‑band interference‑tolerance criteria
- A clear compliance and certification roadmap (includes probable Hardware and Software service bulletins) aligned with FAA implementation timelines
- Supporting engineering documentation suitable for program, certification, and operational use
Industry Significance
FAA NPRM FR Doc 2026‑00051 (Docket 2025-5666) and subsequent Advisory Circular AC 20-199 represents an important step toward formalizing radio‑altimeter interference‑tolerance expectations in an evolving RF environment. FreeFlight Systems is actively engaged in the rulemaking process and prepared to evaluate the RA‑4500 MK II, RA‑5500, and RA‑6500 against the finalized requirements once issued.
We will provide formal compliance evidence and program guidance as soon as FAA performance criteria and test procedures are finalized.
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