Potential Interference Risk to Radio Altimeters from 5G Mobile Technology

This article raises awareness of potential interference to Radio Altimeter systems (Rad Alt) from the ground based 5th Generation (5G) telecommunications infrastructure.

1. The Issue

Radio Altimeters can support a range of functions on board an aircraft and provide critical data for the safe execution of aircraft operation. The roll-out of 5G telecommunications networks continues to expand worldwide at a rapid pace, with many nations electing to allocate currently unused spectrum that is located closer to the Aerospace Reserved Band used by Radio Altimeters, to 5G operations.

Consequently, concern has been raised by several National Aviation Authorities (“NAAs”) that Radio Altimeters may be prone to interference from 5G telecommunications frequencies that could result in loss or malfunction of Radio Altimeter functionality.

The deployment of 5G mobile technology varies by state and is individually managed by state radio regulators. Deployment of 5G mobile technology is across a range of different frequency bands, output powers and other technical variables which dictate the operating environment that radio altimeters will be required to function in.

Although the OTAA’s have no jurisdiction over radio spectrum management and the allocation of spectrum, they do have a responsibility for aviation safety in the Overseas Territories. Some countries have introduced temporary technical, regulatory or operational mitigations on mobile telecommunications providers and/or aviation industry to mitigate against the potential risk of interference. It should be noted that some other NAAs including FAA, CASA and UK CAA have published information bulletins on this subject.

Information received from other NAAs has so far indicated that there have been no confirmed instances where 5G interference has resulted in aircraft system malfunction or unexpected behaviour. It should be noted that in some states, 5G infrastructure is not yet in place and that past performance is not a guarantee for future applications.

2. Operations in the USA

ASSI acknowledges the Federal Aviation Administration's (“FAA”) assessment of the increased risk specific to the United States, along with the release of the associated Airworthiness Directives (“AD”) and the potential for FAA to publish NOTAMs prohibiting certain operations. FAA ADs 2021-23-12 (for fixed wing) and 2021-23-13 (for Rotary Wing) must therefore be followed when operating in the USA where a NOTAM is in place.

3. Action to be Taken

3.1 Operators should ensure their flight crew are aware of the possible implications of radio altimeter malfunctions for the types of aircraft operated; this may be particularly relevant when conducting Precision Instrument Approaches during Low Visibility Operations.

3.2 Where a state, based on safety analysis of its own 5G roll out, has issued a NOTAM or similar directive, OT operators are required to adhere to any state operational restrictions. The absence of a NOTAM does not necessarily imply that interference will not be encountered.

3.3 Flight crew experiencing radio altimeter or autoflight malfunctions should not assume that this has been caused by 5G interference and should follow normal operating procedures for any malfunctions or failures. Although flight crew should be aware of the possibility of 5G interference, any malfunctions observed may well be caused by other factors such as radio altimeter and associated antenna technical failures.

3.4 Any flight crew observations of radio altimeter or autoflight malfunction should be reported using normal company safety reporting procedures. Flight crew should include as much detail regarding the type of malfunction, including duration and location (particularly if during an approach or departure phase), the runway in use and the height above the ground that the malfunction was observed. If the commander assesses that the malfunction resulted in a significant risk to aviation safety, the report should be submitted as an MOR, in accordance with the requirements of OTAR 13.

3.5 Aerodromes should also be aware of the potential risk of interference and associated trends that may emerge, which could impact operations more widely.

4. Queries

For any questions relating to this article, please contact enquiries@airsafety.aero.