Potential Risk of Interference of 5G Signals on Radio Altimeter - Civil Aviation Safety Alert (CASA) No. 2021-08


All Canadian Private, Commercial Air Operators with a Radio Altimeter and Air Traffic Service

File Classification No.: Z 5000-35
RDIMS No.: 17416867
Document No.: CASA 2021-08
Issue No.: 01
Effective Date: 2021-06-15


The purpose of this Civil Aviation Safety Alert (CASA) is to raise awareness of the potential risk of 5G interference and to recommend precautionary operational measures before confirmation of impact of 5G radio waves on radio altimeters.


Innovation, Science and Economic Development Canada (ISED) is the spectrum regulator in Canada. ISED will allow 5G networks and technology in the frequency band 3450-3650 MHz following its auction in June 2021. Additionally, ISED recently decided to allow mobile wireless systems to operate in the frequency band 3650-4000 MHz for 2023. The frequency bandwidth allocated to 5G is close to one used by aircraft radio altimeters (4200-4400 MHz). In some countries in Europe and Asia, 5G is already deployed. Given the worldwide expansion of this technology, Transport Canada was drawn to a recent Radio Technical Commission for Aeronautics (RCTA) report which concludes to a likelihood of disturbance for certain radio altimeter models by 5G radio waves in numerous operational scenarios and most notably at low height (less than 1000 ft) in the frequency band 3700-4000 MHz.

The most undesirable outcome of interference is the indication of an undetected wrong height information given by the radio altimeter. Depending on operations, equipment model and aircraft type, this kind of error could have significantly adverse impacts on flight safety. It may impact Terrain Awareness Warning Systems (TAWS), Traffic Alert and Collision Avoidance Systems (TCAS) and Airborne Collision Avoidance Systems (ACAS), Wind Shear detection systems, flight control systems, and autoland systems (including auto-throttle and automated landing flare and rollout) and loss of situational awareness due to erroneous or unexpected behavior.

Section 602.08 of the Canadian Aviation Regulations (SOR/96-433) and Advisory Circular (AC) 700-005 Use of Transmitting and Non Transmitting Portable Electronic Devices are still applicable, where no air operator shall permit use of a Portable Electronic Devices (PEDs) on board an aircraft except with the permission of the operator of the aircraft and permit the use of non-transmitting PEDs on board aircraft during critical phase of flight.

ISED is committed to keeping Canadians safe. As such, ISED will continue to monitor and study this issue as it develops and, if necessary, may update technical rules in the 3500 MHz band to mitigate potential interference to radio altimeters.

Recommended action

Operators should remind passengers and flight crew that all electronic devices should be carried in the cabin, on their person or in the luggage. If these were placed in checked baggage, they should be turned off and protected from accidental activation.

All 5G PEDs carried in the aircraft should be set to non-transmitting mode so they do not transmit on the cellular networks (e.g. airplane mode) or switched off.

For essential communications, e.g. during emergency medical service operations (EMS), crew should only use 3G or 4G communication devices.

In the event of an actual disturbance of radio altimeter, it is imperative that flight crew report the event to the Air Traffic Service (ATS) as soon as possible. NAV CANADA and ISED will provide guidance on how aviation will report 5G interference events, establish a procedure to alert the aviation community and corrective actions to be implemented.

International operators need to be aware of the potential risk of interference to radio altimeters when operating in countries with different 5G networks and their respective mitigations measures, if any are in place.

Contact office:

For more information concerning this issue, contact a Transport Canada Centre; or contact Michel Drolet, Air Navigation Standards, Frequency Management in Ottawa, by telephone at 1-866-995-9737, by fax at 613-954-4731 or by e-mail at michel.drolet@tc.gc.ca.

Original signed by

Félix Meunier
Director, Standards
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.