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Airlines this week cancelled or rerouted flights heading to certain US airports. Was it due to a surge in Omicron cases, threats of terrorism, or a fault identified in jumbo jets?

No, it is because of radio waves from 5G mobile networks. We are now nearly three years into the roll-out of 5th-generation mobile networks and while the technology hasn't yet revolutionised telecommunications, it has certainly lived up to the safety and reliability claims of the mobile equipment makers. US mobile operators have built out 5G coverage accessible by millions of Americans.

So why has the US aviation sector sounded the alarm about the country's largest mobile operators, AT&T and Verizon, activating 5G networks close to airports? The Federal Aviation Authority claims that the US telcos' use of the C-band radio spectrum could potentially interfere with the radio altimeters which measure how close an aircraft is to the ground. 

Buffering...

That would be a potentially disastrous thing. While there haven't been any reports of the existing 5G networks in the US causing inaccurate altimeter readings, the aviation industry has spooked the telcos to the extent that AT&T and Verizon have paused their build-out of 5G networks using C-band spectrum in close proximity to airports until they sort the issue out.

That's bad news for the US 5G network expansion. So is the threat of interference to altimeters real? It is probably unlikely, but the way the US has set up its spectrum allocation for 5G is a cause for concern. The frequency allocated for AT&T and Verizon in the US is the 3.7 - 3.98 GHz (gigahertz) band. Aeroplane altimeters operate in frequencies between 4.2 - 4.4 GHz.

That means there's just a 220 MHz gap or 'buffer' between the 5G band and altimeter band. Ideally, it should be 400 MHz to avoid any chance of interference. In New Zealand we've completely avoided this problem because 5G here is deployed in the 3.4 - 3.8 GHz radio spectrum band, allowing at least 400 MHz of separation with altimeter bands.

No concern here

In Vodafone's case, the buffer is even larger because its 5G network operates at 3.434-3.497 GHz range. Vodafone's wholesale and infrastructure director, Tony Baird, said the company was "very confident that any US aviation concerns around 5G spectrum bands are not relevant in New Zealand, as our 5G network runs on a lower frequency band (3.5 GHz) meaning interference with aviation transmitters is not a concern in Aotearoa."

"Since 2020 we've been in discussions with local authorities on this topic and will continue to watch the situation closely, as well as work with the aviation industry to allay any concerns," added Baird.

The same message has come from European operators, which also operate 5G in the 3.4 - 3.8 GHz radio spectrum band.

So the US appears to have shot itself in the foot by failing to adequately plan its spectrum allocation and ensure cooperation between the telcos and aviation industry, which have long argued over spectrum allocations anyway.  

AT&T and Verizon bought C-band spectrum licences last year in government auctions, collectively paying US$68.9 billion for them. Even as the bidding was underway, it appears that the FAA hadn't property tested altimeters and issued guidance around spectrum use. 

FAA in the gun

The FAA and other government regulators had years to prepare for the roll-out of 5G near airports and did very little to address safety concerns and work with the telcos to ensure a smooth roll-out. It now faces the wrath of airlines and telcos alike. AT&T and Verizon have paid big money and need to get their C-band spectrum working. This week they were busy switching it on across the US, where it could offer significantly boosted download speeds.

But a buffer will remain in place around airports until a solution is sorted out - or extensive testing satisfies the FAA that the risk of interference with aircraft altimeters is negligible. Airlines are furious about the confusion and disruption caused this week.

The US is already smarting over falling behind in mobile technology as arch-rival China forged ahead, with Huawei taking a lead in the global mobile equipment market while the US was left reliant on equipment from Nokia, Ericsson and Samsung. Now it faces the ignominy of having its next-generation network deployment disrupted and it only has itself to blame. 

It's a good lesson on how not to handle a major technology transition - and a sharp reminder of the fallout that can be the result of bureaucratic inertia and poor cooperation across industries.

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