There was some disturbing news item recently that ‘Air India has announced cancellation of flights to the US starting January 19 in view of the deployment of the 5G operations by the US mobile telcos.

Mobile phone network or cellular network, which is radio communication network, enables wireless communication using mobile devices. Mobile phone network is distributed over land areas called cells, each cell served by at least one fixed-location transceiver, known as a base station. Each cell can be of 30 km radius. Each cell uses a different set of frequencies to avoid interference and provide guaranteed bandwidth within each cell.

Mobile networks started with 1G around year 1979 and have evolved over the years, and now 5G network is ready for implementation. In the US, 5G network will use frequency spectrum 3.3-4.2 GHz. These frequencies are close to the frequencies used by radio altimeters on aeroplanes. Altimeters are used for measuring the height of the flying aircraft above the ground, and also provide data for safety and navigation systems.

Two types of altimeter are in common use in airplanes — barometric altimeter and radio altimeter. The former functions based on the air pressure, and the latter is electronic and functions based on the radar principle by sending a radio signal to ground and analyses the signal reflected from ground to compute the flying height.

Radio altimeter operates in the frequency of 4.2-4.4 GHz, very close to the 5G network band planned in the US and it is feared that the 5G network will interfere with altimeter functioning. Radio altimeters are more accurate than barometric altimeters and have become more important and many times essential in aviation.

Risk to flying

Flying aircraft near 5G network is potentially very risky, In 2020, the RTCA (Radio Technical Commission for Aeronautics), a US aviation guidance organisation, warned of the possibility of catastrophic failures leading to multiple fatalities due to 5G interference, with number of different systems aboard the aircraft malfunctioning, pilots could be mislead during landing. US aviation regulator FAA (Federal Aviation Administration) has also issued a similar warning.

US mobile networks AT&T and Verizon had planned to roll out the 5G services this month. Many US airlines expressed their concern and many other country airlines have canceled flights to the US as a precautionary measure.

Making flying safe

Some technocrats have suggested not to use radio altimeters where there could be a risk of serious interference. But that will restrict the ability of aircraft to land in poor visibility. The FAA has plans to establish temporary buffer zones around airports, where 5G providers will limit their activities.

FAA has also begun identifying altimeters, which can be used safely in areas where 5G has been deployed and it has directed airlines to replace altimeters which are not reliable enough. It has also identified airports where GPS systems can be used to guide approaching aircraft rather than radio altimeters.

But airlines are asking for 5G network not be activated at all within two miles of affected airports. The good news is Verizon and AT&T have agreed to “temporarily” delay the roll out of 5G.

Situation in other countries

The situation in places other than US is not bad. In the EU, 5G networks operate at lower frequencies than in the US, reducing the risk of interference. 5G masts are restricted to operate at lower power. In France, there are so-called “buffer zones” around airports where 5G signals are restricted, while antennas have to be tilted downwards to prevent potential interference.

In India, telcos are expected roll out 5G services later in 2022. The spectrum planned for 5G is 3.3-3.6 GHz which is faraway from altimeter frequencies and thus roll-out could go on without affecting aircraft operations.

Many other countries are planning 5G spectrum allocation cautiously to avoid the interference problem.