Potential Risk of Interference of 5G Signals on Radio Altimeter - Civil Aviation Safety Alert (CASA) No. 2023-06


All canadian private, commercial air operators with a radio altimeter and air traffic service

File Classification No.: Z 5000-35 U
RDIMS No.: 19941976
Document No.: CASA 2023-06
Issue No.: 01
Effective Date: 2023-11-24


The purpose of this notice is to complement Civil Aviation Safety Alert (CASA) 2021-08 regarding potential risks of 5G interference on aircraft.

Mitigation measures to safeguard Canada’s aviation system are being considered, particularly for aircraft that are equipped with non-5G tolerant Radio Altimeters, as well as to provide additional safeguards for areas that are not covered by Innovation, Science and Economic Development Canada’s (ISED) exclusion and protection zones. Additional mitigation measures deemed necessary will be communicated through a subsequent Civil Aviation Safety Alert and future Airworthiness Directives. A mandatory retrofit is under consideration to ensure that aircraft are tolerant to the Canadian 5G environment.


ISED is the spectrum regulator in Canada. Since December 2021, ISED has allowed flexible use networks and technology (including 5G) in the frequency bands 3450 to 3650 MHz (3500 MHz). Further, ISED will allow flexible use networks and technology (including 5G) in the frequency bands of 3650 to 3900 MHz (3800 MHz) following its auction that began on October 24, 2023. Deployment in the 3800 MHz band may occur as early as April 1, 2024. Additionally, ISED recently concluded a consultation on non-competitive local licensing framework to operate in the frequency bands of 3900 to 3980 MHz.

The frequency bands allocated to these services are close to the one used by aircraft radio altimeters (4200-4400 MHz). Data gathered by the US Federal Aviation Administration (FAA), ISED, the Radio Technical Commission for Aeronautics and others, have shown that there exists a likelihood of disturbance for certain radio altimeter models by 5G radio waves in numerous operational scenarios in the frequency bands of 3450 to 3980 MHz. The most undesirable outcome of interference is the indication of undetected erroneous height information given by the radio altimeter. Some civil aviation authorities around the world have started to issue and implement mitigation measures to curtail the risks to aviation safety associated with the 5G environment.

In July 2023, ISED established technical rules in the 3450-3900 MHz bands to mitigate potential interference to radio altimeters, which extends the technical rules for the 3450-3650 MHz band (3500 MHz) that were published by ISED in November 2021. The main temporary protection measures include:

  • exclusion and protection zones to mitigate interference to aircraft having a certain level of 5G tolerance at certain runways at 35 airports covering 93% of air traffic in Canada, effective until January 1, 2026.
  • Reduced fundamental emissions power levels at the runways at the 35 airports having protection and exclusion zones, implemented by E.I.R.P. elevation mask. These airport elevation masks are effective until January 1, 2026, for the 3500 MHz band and until January 1, 2028, for the 3800 MHz band; and
  • Reduced fundamental emissions power levels based on degree of antenna uptilt above the horizon, nationwide, to minimize skyward emissions from 5G base stations. These national antenna uptilt and power limits are effective until January 1, 2026.

It is important to note that these protection measures may be different than those in other countries, given that each country determines what is required based on their country’s spectrum environment.

Transport Canada has identified possible interference to radio altimeters that are not tolerant to 5G interference from 3450-3980 MHz frequencies at or above a specific power spectral density (PSD) curve threshold, which may affect aviation safety. Transport Canada is considering issuing Airworthiness Directives (ADs) to apply aviation limitations to aircraft that may not be tolerant to the Canadian 5G environment. A mandatory retrofit is also under consideration. TC is studying the equivalency of the Canadian spectrum environment to the US. If the Canadian environment is determined to be worse than the US spectrum environment, this could mean that not all aircraft equipped with radio altimeters deemed compliant with Federal Aviation Administration Airworthiness Directives may be considered tolerant by Transport Canada to the Canadian 5G environment. Protected airports only offer protection to aircraft that can withstand a certain level of 5G interference for fundamental emission (i.e., Federal Aviation Administration defined Group 3, pending additional analysis). Non-radio altimeter tolerant airplanes that are Group 1, and 2 airplanes according to the Federal Aviation Administration definition will face stringent limitation where 5G may have been deployed.

Recommended action:

Operators should continue to follow the recommendations in CASA 2021-08. In addition, Autoland procedures to any airport not included in the list of airports with exclusion and protection zones defined in ISED’s SRSP-520 Issue 3 are not recommended due to possible interference to Radalt from 5G network resulting in degraded system performance.

Operators should continue to identify all possible indications that might be evidence of possible radio altimeter disturbance in their aircraft and ensure this information is provided to flight crews as specified in CASA 2021-08.

In the event of an actual disturbance of radio altimeter, it is imperative that flight crew report the event to the Air Traffic Service as soon as possible, regardless of the location of the occurrence be it domestic or foreign airspace. Pilot in command and operator are to complete the ‘Radio Altimeter Disturbance/Interference Report’ in Appendix A: Radio Altimeter Disturbance/Interference Report.

Transport Canada is committed to ensuring the safety of the aviation system during the deployment of 5G networks, while minimizing impacts to the Canadian aviation industry to the extent feasible and ensuring aviation safety. Canada aims to align with the US from an aviation limitations standpoint to support mitigating aviation safety risk associated with 5G emissions.

Transport Canada continues to engage its United States and other counterparts as well as its aviation stakeholders to assess existing aviation safety risks in all weather conditions.

Contact office:

For more information concerning this issue, contact the Civil Aviation Communications Centre: https://tc.canada.ca/en/aviation/civil-aviation-contacts-offices/civil-aviation-communications-centre-contact-form.

Appendix A: Radio Altimeter Disturbance/Interference Report

Available online:

Original signed by

Stacey Mason
Standards Branch
Civil Aviation


The Transport Canada Civil Aviation Safety Alert (CASA) is used to convey important safety information and contains recommended action items. The CASA strives to assist the aviation industry's efforts to provide a service with the highest possible degree of safety. The information contained herein is often critical and must be conveyed to the appropriate office in a timely manner. The CASA may be changed or amended should new information become available.