As you may know, in the last weeks you’ve probably seen talk of 5g networks interfering with planes in the US. Earlier this year some companies like Emirates, Air India, All Nippon Airways, Japan Airlines, Lufthansa and British Airways all announced changes to some flights, citing uncertainty about potential interference between new 5G cell phone services and critical airplane technologies.
The problem is occurring with the radioaltimeter. Each airliner uses two R ALT units which send radio waves to the ground and measure the height between the landing gear wheels and the ground with high accuracy, the main purpose is to schedule correctly the flare manoeuvre before touchdown. Another important purpose is to protect the flight against proximity to the terrain in the terminal phases of the flight. R ALT is a major information source for the Autoland function of the AFCS, EGWS / TAWS, and TCAS. Without correct R ALT measurements, the flare maneuver could be too early or too late, and consequently dangerous. In the United States, 5G services launched in 46 markets on January 19, using frequencies in a radio spectrum called the C-band. These frequencies can be close to those used by radio altimeters, an important piece of safety equipment in aircraft. To make sure that this does not lead to hazardous interference, the FAA requires that radio altimeters are accurate and reliable. Because the proposed 5G deployment involves a new combination of power levels, frequencies, proximity to flight operations, and other factors, the FAA must impose restrictions on flight operations using certain types of radio altimeter equipment close to antennas in 5G networks. Approved radio altimeters allow commercial aircraft to continue low-visibility landings in the 5G C-Band deployment areas.
5G technology was deployed in Europe and in other parts of the world without aviation incidents, but the concerns for this problem in the US are justified since the radio band attributed to this service is 3.7-3.98 GHz in the US, very close to the 4.2-4.4 GHz radio band which R ALT is using, with just a 200 MHz buffer. In the European Union, the 2019 approval of 5G frequencies in the 3.4-3.8 GHz range guaranteed twice as much for this buffer. South Korea limits its band to 3.7 GHz, so the buffer is 500 MHz. No incidents have been recorded in these areas. The concern that just a 200 MHz buffer would cause disruptions in the R ALT signals is legitimate. Did we see similar situations in the past? This resembles a situation of a decade ago also in the US with GPS signal interference with a new metropolitan area internet service, and after several incidents, the mobile communications operators lost their license. Aviation is a direct 4% of the world economic activity and 12% including co-lateral activities, so it is too important to be compromised.
FAA also issued multiple NOTAMs in order to make sure that pilots know about the issues that 5G can bring during the flight. But this problem is not new, in 2021 the French Civil Aviation Authority had already warned of the same issue, so the phone masts near the airport were limited in power in France, as they were in Canada.
Until further development of this uncertainty over 5G, we can only wait to see what happens across the ocean.