Early in January, AT&T and Verizon made news by voluntarily delaying the activation of their much-vaunted 5G service on towers near some US airports, following warnings from the aviation industry and the Federal Aviation Administration that the rollout of 5G would pose a risk to aircraft and potentially cause flight cancellations – or worse.

The telecommunications giants had originally been scheduled to fire up their C-band 5G networks late last year. However, as the deployment loomed closer, calls from the airlines and aircraft manufacturers to revisit the safety questions around 5G technology grew louder, so the telecoms agreed to delay until Jan. 5.

In December, the FAA issued a pair of airworthiness directives based on concerns that potential interference from C-band 5G wireless services could pose a safety risk to air traffic and lead to flight diversions. Then on the eve of the rollout, in a letter to the White House, the FAA and Federal Communications Commission, the CEOs of major US carriers urged that the planned implementation of 5G be halted within two miles of many US airports. "Unless our major hubs are cleared to fly, the vast majority of the traveling public will essentially be grounded," they wrote in the letter.
As part of a stopgap solution, the FAA announced the creation of buffer zones around 50 airports in the US, including 17 of the top 20 busiest airports in the country. Still, FAA warned that “even with the temporary buffer around 50 airports, 5G deployment will increase the risk of disruption during low visibility.”

When the concerns were first raised, the wireless carriers had agreed to limit C-band 5G power levels around airports, and later consented to the exclusion zones where they would forego deploying 5G at all – but only for six months – a step that is a permanent feature of France’s 5G services. Nevertheless, these steps were not enough to allay the fears of airlines and aviation regulators, and under pressure from the Biden administration, both AT&T and Verizon relented, further delaying the rollout of 5G services near airports by an additional two weeks, until Jan. 19.

Since then, the FAA has fast-tracked studies on the radio altimeter equipment used in commercial aircraft to determine which models are able to perform low-visibility landings when 5G C-band is deployed. As of the end of January, agency said it has determined that around 90 percent of the commercial aircraft fleet flying in US airspace – including most Boeing and Airbus models – can operate safely near 5G towers using C-Band spectrum.

Despite all this, the wireless providers and aviation industry are still at odds over the impact of 5G C-band interference on aircraft systems – and are likely to remain so. To understand why, we need to look at the history.

The 5G Backstory
First, a short primer on 5G. These next generation devices can transmit data up to ten times faster than current 4G technology. However the high-frequency band which offers those data rates and speed has a huge capacity but short range. Lower bandwidth frequencies cover a wider area but have limited capacity. The C-band is a mid-spectrum frequency band which gives 5G carriers a workable compromise between the two.

The squabble over aviation safety concerns actually goes back to the beginning of 2021, when the Federal Communications Commission auctioned off the C-band spectrum, most of it to Verizon and AT&T. The frequencies allocated to mobile phone providers are between 3.7 to 3.98 GHz. As the federal agency responsible for setting the bandwidth, the FCC concluded from its own technical studies that this band of frequencies posed little risk of causing interference with other spectrum uses – such as the radio altimeters in aircraft.

The safety issues arise from the C-band frequency’s proximity to the part of the spectrum used by these instruments, which operate in the 4.2-4.4 GHz bandwidth. Radio altimeters let pilots know the altitude of their plane, and are critical for aircraft systems during automated landings, especially in low visibility conditions, and to help detect dangerous windshear. The closer the 5G bandwidth gets to the frequencies used by aircraft, the greater the possibility for interference. Thus the airlines’ concerns about the buffer, also known as “guard bands,” between the frequencies.

But Why There and Not Here?
Verizon and AT&T argue that 5G has already been deployed by other countries around the world without raising aviation safety concerns. However, there are some important differences.

For example, in 2019 the European Union set standards for mid-range 5G frequencies in the 3.4-3.8 GHz range, resulting in a guard band that’s about twice that designated in the United States. At this point, according to the European Union Aviation Safety Agency, the controversy was specific to US airspace. “At this stage, no risk of unsafe interference has been identified in Europe,” EASA said.

In South Korea, the 5G band is lower still at 3.42-3.7GHz band and there have been no reports of interference with aircraft since the system was inaugurated in April 2019. Meanwhile, the UK’s Civil Aviation Authority has reportedly been quoted as saying, “There have been no reported incidents of aircraft systems being affected by 5G transmissions in UK airspace.”

Lessons Learned
In a filing with the FCC, the wireless trade group CTIA said that “wireless carriers in nearly 40 countries throughout Europe and Asia now use the C-Band for 5G, with no reported effects on radio altimeters that operate in the same internationally designated 4.2-4.4 GHz band.”

Notwithstanding the telecomm industry’s confidence, as the Jan. 19 deadline for 5G rollout approached, a number of domestic and international carriers —Emirates, JAL, ANA and Air India—cancelled flights out of caution.

Although this contretemps over public safety between two behemoth industries – aviation and telecommunications – is plenty worrisome, what may be of more concern is the lack of coordination, bureaucratic infighting and pettifoggery between the government regulators – the FAA and the FCC – charged with overseeing them. If these agencies can’t even get well-established apparatus like radio altimeters right, what will happen with the introduction of ever more complex systems – like driverless cars and air taxis – at the intersection of technology and transportation?

Another lesson learned: No matter what other players are sitting at the table, aviation safety should always hold the high card.