Canadian authorities are warning operators of the potential risk of interference to radio altimeters arising from 5G communications networks, following auction of part of the frequency spectrum.
The country’s spectrum regulator, ISED, is auctioning the 3.45-3.65GHz band during June and will allow mobile wireless systems to operate in the adjacent 3.65-4GHz band in 2023.
But these frequencies are close to the 4.2-4.4GHz band used by radio altimeters, which provide a direct measurement of aircraft height above terrain during approach and other phases of flight at low altitude.
The US-based regulatory guidance organisation Radio Technical Commission for Aeronautics produced an analysis of 5G interference in October last year, after the aviation industry expressed concerns to the US Federal Communications Commission during the 5G deployment process.
RTCA says its assessment included testing “many representative radio-altimeter models”, to determine their tolerance to 5G interference, and examination of “multiple real-world operational scenarios” for civil aircraft in which such interference might directly affect safety.
It concludes that there is a “major risk” that 5G systems using the 3.7-3.98GHz band “will cause harmful interference” to radio altimeters on “all types” of civil aircraft – including those operating commercial services.
“The results of the study performed clearly indicate that this risk is widespread and has the potential for broad impacts to aviation operations,” it adds.
Commercial air transport aircraft, it says, may be impacted by 5G at altitudes up to 4,000ft and at distances of just over 0.4nm from a 5G base station. It does state that adequate mitigation might be achieved by base-station deployments that take departure and approach flightpaths into account.
But the analysis shows a “much broader” operational impact for regional, business and general aviation, with interference levels exceeding tolerance limits across the majority of the relevant 2,500ft altitude range, at all tested lateral distances from the base station.
RTCA also found the impact was not limited only to intentional 5G system emissions in the 3.7-3.98GHz band but also spurious emissions from such systems within the protected 4.2-4.4GHz band.
Transport Canada says its attention has been drawn to the RTCA’s conclusions regarding disturbance to certain radio altimeters, notably at heights of less than 1,000ft, and is issuing a civil aviation safety alert to raise awareness of the potential risk.
It is also recommending precautionary operation measures ahead of confirmation of possible effects.
“The most undesirable outcome of interference is the indication of undetected wrong height information given by the radio altimeter,” it says.
“Depending on operations, equipment model and aircraft type, this kind of error could have significantly adverse impacts on flight safety.”
Transport Canada says operators should remind passengers and crews that all electronic devices should be carried in the cabin, on their person or in luggage. If these are placed in checked baggage, they should be turned off and protected from accidental activation.
All 5G personal devices carried should be turned off or set to non-transmitting modes, it adds, and any essential or emergency communications should be limited to 3G or 4G devices.
Transport Canada is also urging crews to report any disturbance to radio altimeters to air traffic control as soon as possible. Air navigation service Nav Canada and ISED are to provide guidance on reporting such events.