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There have been several reports discussing the possible disruption of US aviation once mobile networks AT&T and Verizon deploy new 5G services.
Dr Guy Gratton, Associate Professor of Aviation and the Environment at Cranfield University, said:
“Airliners provide themselves with additional height information on final approach and landing using a device called a Radio altimeter, which is a simple enough machine – a couple of antennas on the underside of the aeroplane transmit and receive on a discrete frequency, giving accurate (within 10ft or so) readings of the aeroplane’s height above the ground. This is supplementary to primary guidance information, which is most likely from radio beacons (ILS or Instrument Landing System) or GPS.
“The problem is global, because RadAlts use the same radio frequency range everywhere, as is the new 5G technology – and essentially the two are using similar frequencies and thus there is potential for interference. Nonetheless in the USA where the gap between allocated RadAlt and 5G frequencies is smaller, and the 5G transmission power is greater, the risk is greatest. The American aviation and radio authorities are working this problem right now, and have delayed 5G rollout in some areas, but there’s still little robust published research about the scale and severity of the problem so for now everybody’s playing very safe.
“If we cannot trust RadAlt, then airliners will cease to have such accurate information about their height in the final stage of a landing. Whilst flight guidance remains available from “precision” sources (ILS, and enhanced GPS such as WAAS in North America or EGNOS in Europe) and from non-precious sources (non enhanced GPS, and some legacy systems such as ADF – Aerial Direction Finder) the quality of what the pilot knows is degraded. The implications are almost certainly that where a radio frequency survey hasn’t ensured a totally frequency specific RF sterile environment in the approach path, and you could envisage that say at Heathrow where the approach lies over a lot of human habitation, additional safety margins will have to be added, probably making auto-land to a fogged in runway prohibited.
“So, what I’d anticipate is that this concern, until solved, may make it harder to operate from some airports, in poorer (fog or low cloud) weather conditions, making diversions and cancelled flights more likely in those conditions. Where flying conditions are good (say cloudbases above 200ft, visibility better than 800m – which would be the current limits for a standard ILS approach), I’d expect to see some procedures being changed, but likely no impact upon the ability to operate.
“A side issue here for the UK specifically is that we have discontinued our involvement in the European EGNOS GPS enhancements with Brexit, but failed so far to replace that with anything else, we may be more effected than other countries where that exists – however that won’t be in many places as the classical ILS system will fill that space, which are in place at virtually all major airports – the impact will be greater at smaller airports served by smaller business jets and the like, but which haven’t got the expensive ILS infrastructure in place. For those, there may cease to be any precision approach data, limiting aeroplanes landing there to still greater minima which are likely to be around a 350ft cloudbase and 1000m visibility (all of these numbers will vary with local conditions such as terrain, and the specific navigation aids being used).
“Clearly on what most of us might regard as a “nice day” with good visibility and high clouds, there should be few problems – this is very much about the ability to operate reliably in poor conditions. Safety will never be compromised because regulations will be modified to ensure minimum standards always apply: the problem here will be of cancelled or diverted flights in some conditions.
“The solution to this problem may be through surveying and operating experience showing there’s not an issue, but more likely it will require expensive modification of RadAlt systems on airliners to either encode their signals to ensure no confusion between those and 5G, or to move their working radio frequency ranges to those not used by anything else.”
Prof Maziar Nekovee, Professor of Telecomms and Mobile Technologies at the University of Sussex, said:
“The concerns about 5G’s impact on the aviation industry is mainly a US issue for two main reasons.
“The maximum transmit power level emissions of 5G mobile infrastructure (base stations) that are set by national telecom regulators (Ofcom in UK, FCC is USA) are about two times higher in the US than in the UK and most other countries so this may increases the likelihood of interference with altimeters used for commercial airplanes’ radar which also operate in C band, the designation of the electromagnetic spectrum in the microwave range of frequencies, albeit at a higher frequency.
“It is also significant to note that the allocation of C-bands to operators in USA by the FCC was over two years later than the UK and many other countries. 5G in C-band has been deployed for over three years now in the UK without any evidence of causing harmful interference to altimeters.
“However, both in the US and in the UK , the portions of C-band allocated to 5G systems (up to 4 GHz) has a gap of 200 MHz with the portion of C-band used for altimeters (4.2-4.4 GHz). This is a huge gap (guard band) (e g as compared to many other systems operating in adjacent frequencies) between the two systems so, any ‘spillage’ from 5G transmitter emissions into the altimeter frequencies than can cause interferences is extremely unlikely even in the US.
“5G transmitters have deploy sophisticated digital signal processing algorithms and excellent filters that ensure spillage of radiated power outside of their operating band is extremely low and tails off very quickly following a pattern known as the emission mask which is carefully stipulated by telecom regulators. This is partly to maximise the use of 5G spectrum for operators using adjacent 5G bands and to avoid harmful interference to other systems operating in adjacent bands.
“Given the sophistication of 5G transmitters, any remaining spillage that might get picked up by some of the altimeter’s equipment’s could be because their receiver filters are not as sharp as they should be.”
eg https://www.bbc.co.uk/news/business-60042178
Declared interests
None received.