Radio altimeter requirements due to 5G transmissions - (CD 2513AS)

This consultation asked for comments on proposed amendments to the Part 91, 121, 133 and 135 Manuals of Standards (MOS), and a direction under CASR Subpart 11.G to Part 129 Foreign Air Transport Air Operator's Certificate (FATAOC) holders, and New Zealand AOC holders with Australia New Zealand Aviation (ANZA) privileges.

It was proposed to require radio altimeters fitted to aircraft used for the conduct of low visibility approaches, being SA CAT I, SA CAT II, CAT II and CAT III instrument approach procedures (IAPs), and RNP-AR IAPs, to be compliant with the interference tolerance curves in relevant FAA airworthiness directives from 1 April 2026.

The proposals were made because measures imposed by the Australian Communications and Media Authority (ACMA) to protect radio altimeters from 5G transmissions are due to end on 31 March 2026.

About this consultation

The consultation opened on 7 July 2025 and closed on 3 August 2025, with some late responses accepted until 11 August 2025.

Prior to the consultation, CASA distributed information about future radio altimeter upgrade requirements to industry participants:

• In October 2024, CASA established a page on its website advising the industry of the need to upgrade radio altimeters prior to the cessation of the ACMA protection measures.
• In November 2024, similar information was sent to Part 129 FATAOC holders, and to the Civil Aviation Authority of New Zealand (CAA NZ) who was requested to advise NZ AOC holders with ANZA privileges.
• A further reminder was sent to operators in March 2025.

Following the initial review of responses, CASA requested further details from some respondents on the impact the proposed amendments would have on their operations.

We received 14 responses with 9 respondents completing the online survey and 5 providing comments by email.

Of the 14 responses received:

• nine responses were sent on behalf of airlines
• four responses were received from individuals
• one was from an aircraft manufacturer.

Summary of feedback

Respondents understood and accepted the need for the proposed MOS amendments, however most requested that the effective date (1 April 2026) be delayed.

Request to delay commencement date

Most respondents stated it would not be possible to upgrade all their relevant aircraft prior to the effective date. Challenges in upgrading radio altimeters include the availability of parts, cost, and logistics considerations associated with taking aircraft off-line for the upgrade.

Respondents mentioned that service bulletins for upgrading radio altimeters were not yet available for some aircraft and would need to be developed by the aircraft manufacturer. For a few older aircraft types and models, the radio altimeters could only be upgraded by a third-party supplemental type certificate (STC).

One respondent mentioned that it was planning to apply to CASA for approval to conduct RNP‑AR IAPs in 2026 and requested a 3-year delay to the commencement date for the proposed amendments to allow it to upgrade its fleet of aircraft.

Suggested delays in the commencement of the proposed amendments ranged from 6-9 months to 3 years, with respondents suggesting that the current ACMA measures be maintained to protect radio altimeters during this period.

Impact on airline operations

Respondents stated that the impact of not being able to conduct the prescribed IAPs on their operations could include flight delays, diversions of flights to other airports and flight cancellations. The impact would be experienced when meteorological conditions were such that the prescribed IAPs were needed to land at a given airport but could not be undertaken because the aircraft had not been upgraded.

RNP-AR instrument approach procedures

Feedback specifically in relation to the inclusion of RNP-AR IAPs in the prescribed IAP list caused CASA to revisit the RNP-AR aspect of the proposal.

The FAA initially included RNP-AR IAPs in the list of operations prohibited in the presence of 5G transmissions, but subsequently removed it for the following reasons:

1. 1. RNP-AR IAPs are not directly reliant on inputs from the radio altimeter
   2. while the US aviation industry expressed concerns about the reliance of RNP-AR IAPs on terrain awareness and warning systems (TAWS), and the TAWS use of radio altimeter data, the FAA maintained that even though an aircraft must be fitted with TAWS to receive an RNP-AR IAP approval, TAWS is not required to fly the IAP
   3. the risk of erroneous TAWS warnings in the presence of 5G transmissions was not only limited to RNP-AR IAPs, and would be addressed in the US by requiring all transport and commuter airplanes to be fitted with radio altimeters compliant with the AD from 1 February 2024 (8 months after the AD became effective)
   4. in conjunction with this, the FAA obtained agreement from the major telecommunications companies to implement voluntary restrictions on 5G stations deployed near some airports.

When the FAA revised the AD, CASA did not remove RNP-AR IAPs from the list of operations considered susceptible to 5G transmissions. At that stage, the key safety considerations were:

1. 1. it appeared that there was still a risk of spurious warnings to systems connected with the radio altimeter (e.g. TAWS) during the approach in the presence of 5G transmissions
   2. unlike in the US, this risk was not mitigated by a proposed mandate requiring all operators engaged in air transport operations to upgrade radio altimeters
   3. additional considerations included the different 5G operating conditions in Australia (transmitter power, frequency bands) and the fact that there was no voluntary agreement with the telecommunications companies in Australia to restrict 5G station operations.

CASA's further analysis has confirmed that while TAWS provides an additional level of safety during RNP-AR IAPs, the procedure design does not rely on it. Although the FAA concluded that an erroneous radio altimeter output could affect the aircraft’s allowed maximum bank angle, CASA's view is that if this resulted in the course being unable to be accurately flown, pilots would receive an '“unable RNP' message and take appropriate action. CASA acknowledges that this combination of circumstances could still result in a pilot being distracted by a spurious TAWS alert while flying an RNP-AR IAP. However, CASA has assessed that this risk is acceptably low as the aircraft automation will also alert the pilot that the IAP needs to be discontinued.

Considering the FAA's actions, and CASA's review following the consultation feedback, CASA has decided to remove RNP-AR IAPs from the proposed radio altimeter upgrade requirement.

AMOCs/Exemptions

One respondent requested that if the protection measures were not extended, then CASA should establish an alternative means of compliance (AMOC) process to approve aircraft which have not been upgraded to conduct the prescribed operations.

Under the civil aviation legislation, technically an AMOC applies to requirements implemented via airworthiness directives, which CASA is not issuing in relation to this matter. However, CASA understands the intent of the respondent's feedback for CASA to establish a legal mechanism for the approval of alternative risk controls.

CASA's assessment is that the existing exemption process already provides a sufficient ability for the approval of alternative risk controls. Subpart 11.F of CASR sets out the legislative requirements for exemptions and CASA's website provides advice regarding the exemption process and links to relevant guidance materials.  

Where the proposed rules would apply

Some respondents made comments indicating a belief that the proposed amendments would apply to Australian registered aircraft and aircraft operated by NZ AOC holders with ANZA privileges operating outside Australia.

The proposed amendments only apply to aircraft operating within Australian territory.

The use of 5G in radio frequency bands close to the radio altimeter band varies in different countries. There are differences in the frequency bands, permissible transmitter power levels and restrictions imposed for aviation. Aircraft operators need to comply with the applicable rules of each country or jurisdiction.

Other comments

One respondent mentioned that they had analysed reports of interference to radio altimeters over a 4½-year period (October 2021 to March 2025) and they concluded that the incidence of 5G related interference was extremely rare.

CASA notes this feedback but advises that ACMA only began issuing licences for the current generation of 5G stations in the first quarter of 2024, and this was accompanied by the measures introduced to protect radio altimeters from 5G transmissions. Therefore, the analysed reports do not contain information relevant to the performance of non-upgraded radio altimeters in the absence of the current protective measures.

Two respondents noted that radio altimeter data was used by other aircraft safety critical systems such as terrain avoidance and warning systems (TAWS), enhanced ground proximity warning systems (EGPWS) and flight envelope protection systems.

Two respondents requested that consideration be given to using some of the funds obtained from releasing spectrum for 5G transmissions to support the aviation industry to upgrade radio altimeters. CASA acknowledges the cost involved in upgrading aircraft radio altimeters, however this is not a matter within CASA's remit.

CASA will continue monitoring the situation but at this stage considers there is insufficient evidence to warrant a requirement for all radio altimeters to comply with the FAA AD. When purchasing new aircraft or replacing radio altimeters, aircraft operators are encouraged to opt for units which offer the highest protections against RF interference. Aircraft operators are also encouraged to keep reporting, to CASA, incidents of suspected interference to radio altimeters caused by 5G stations.

Next steps

CASA appreciates the feedback it has received as part of the consultation process and would like to thank all those who made a submission.

CASA will proceed with the proposed amendments in relation to low-visibility approaches.

CASA will exclude RNP-AR IAPs from the list of operations which require fitted radio altimeters to be compliant with the interference tolerance curves in the relevant FAA ADs.