SAB-001-21 — Radio Altimeters and Technical Rules in the 3450-3650 MHz Band (3500 MHz Band)

March 2021

Innovation, Science and Economic Development Canada (ISED) is monitoring international developments regarding the use of radio altimeters in the 4200-4400 MHz band and their potential to receive interference from future flexible use operations in the 3450-3650 MHz band (hereinafter referred to as the 3500 MHz band).

Radio altimeters

Radio altimeters are sensors installed on most civil and military aircraft and operate in the 42004400 MHz band. They continuously measure an aircraft’s altitude above ground level in flight and provide direct measurement of its clearance over terrain and obstacles. They also feed information to other systems on board the aircraft, including the automated landing and collision avoidance systems.

International spectrum regulators, including ISED, have recently become aware of studies that have shown a possibility of interference to radio altimeters from signals outside their band of operation, which could include signals from future flexible use deployment of 5G systems in 3500 MHz spectrum around airports and heliports.

New standards for radio altimeters are expected to be available in 2022 to address these interference concerns. However, it could take several years to implement, certify and deploy new equipment on existing aircraft.

International developments

Regulators around the world are currently examining the need for measures to protect radio altimeters on aircraft when considering flexible use in bands below 4200 MHz. Some regulators (e.g. France, Japan) have decided to implement measures, such as operational restrictions on flexible use systems near airport runways and around heliports.

Conversely, other regulators (e.g. the United Kingdom, United States, and Australia) have not, to date, imposed any specific requirements for protection of radio altimeters with respect to use of the 3500 MHz band.

Additional international studies are underway to assess the potential interference to radio altimeters from flexible use below 4200 MHz.

Future measures

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.

For questions, please email

March 26, 2021
Martin Proulx
Director General
Engineering, Planning and Standards Branch