5g c-band Rotorcraft

Contiguous United States

July 1, 2023, until Further notice

The FAA has placed limitations on all rotorcraft equipped with a radio altimeter, that are not radio altimeter tolerant (they do not demonstrate the tolerances specified in Figures 1 and 2 below)ⁱ. The FAA determined that radio altimeters cannot be relied upon to perform their intended function if they experience interference from wireless broadband operations in the 3.7 – 3.98 GHz frequency band (5G C-Band). Radio altimeter anomalies that are undetected by the automation or pilot, particularly close to the ground, could lead to loss of continued safe flight and landing. Additionally, radio altimeter anomalies could lead to increased flightcrew workload and flightcrew desensitization to warnings. Relevant 5G C-Band information in the contiguous U.S. can be found on the FAA’s website: www.faa.gov/5g.

The FAA developed interference tolerance requirements for radio altimeters that can be used across the affected fleet. A framework and method to demonstrate a rotorcraft is “radio altimeter tolerant” is described in FAA’s policy statement, Demonstration of Radio Altimeter Tolerant Aircraftⁱⁱ. A ‘‘radio altimeter tolerant rotorcraft’’ is one for which the radio altimeter, as installed, demonstrates the tolerances specified below and in Figures 1 and 2:

1. Tolerance to radio altimeter interference, for the fundamental emissions (3.7-3.98 GHz), at or above the power spectral density (PSD) curve threshold specified in Figure 1; and
2. Tolerance to radio altimeter interference, for the spurious emissions (4.2-4.4 GHz), at or above the PSD curve threshold specified in Figure 2.

A “non-radio altimeter tolerant rotorcraft” is one for which the radio altimeter, as installed, does not demonstrate the tolerances specified in Figures 1 and 2. The FAA published an Airworthiness Directiveⁱⁱⁱ to address the unsafe condition for “non-radio altimeter tolerant rotorcraft.” The FAA strongly urges operators of foreign-registered rotorcraft to voluntarily comply with the actions required by the U.S. Airworthiness Directives (AD) related to 5G C-Band interference¹.

The Rotorcraft AD prohibits the following operations, applicable everywhere in the contiguous U.S., to include the airspace overlying the waters up to 12 nautical miles from the coast (including from the islands of those states):

1. Performing approaches that require radio altimeter minimums for rotorcraft offshore operations. Barometric minimums must be used for these operations instead.
2. Engaging hover autopilot modes that require radio altimeter data.
3. Engaging Search and Rescue (SAR) autopilot modes that require radio altimeter data.
4. Performing takeoffs and landings in accordance with any procedure (Category A, Category B, or by Performance Class in the Rotorcraft Flight Manual or Operations Specification) that requires the use of radio altimeter data.

Figure 1 –Fundamental Effective Isotropic PSD at Outside Interface of Rotorcraft Antenna 

Figure 2 Spurious Effective Isotropic PSD at Outside Interface of Rotorcraft Antenna 

(See https://www.regulations.gov/document/FAA-2022-1647-0095)

(AFS-400, 1 June 2023) [Published 6/23/23]

ⁱ The FAA uses a layered approach to safety; therefore, more than one airworthiness directive may apply. AD 2023-11-07 applies to helicopters equipped with a radio altimeter. Check manufacturer operator messages for any further information or restrictions.

ⁱⁱ FAA Policy Statement Demonstration of Radio Altimeter Tolerant Aircraft. Search policy number: PS-AIR-600-39-01 in Dynamic Regulatory System, AVS/AIR Policy Statements, Memos and Deviations: https://drs.faa.gov/browse/POLICY/doctypeDetails

ⁱⁱⁱ Airworthiness Directives; Various Helicopters (AD 2023-11-07). Search AD Number in Dynamic Regulatory System, AD Final Rules: https://drs.faa.gov/browse/ADFRAWD/doctypeDetails