Why do American airlines say 5G networks will ground their planes?

AIRLINE PASSENGERS are familiar with being asked to turn off their phones before take-off. Now, in America at least, the airlines want mobile-phone companies not to turn on their networks in the first place. On January 17th the bosses of several American airlines warned of a “catastrophic” crisis unless the mobile firms delay switching on parts of their shiny new 5G networks, which they plan to do on January 19th. Large numbers of aircraft could be rendered unusable, claimed the heads of Delta, United, Southwest and others. “The vast majority of the travelling and shipping public will essentially be grounded,” they wrote in a letter to the White House and America’s communications and air-travel regulators. Are they right? And how might 5G networks play havoc with planes?

The airlines are worried about supposed interference between 5G transmitters near airports and radar altimeters, instruments on planes that use radio waves to determine an aircraft’s altitude. The Federal Communications Commission (FCC), which regulates commercial use of the radio spectrum in America, studied the question in 2020 and concluded the two systems could work together. The Federal Aviation Administration (FAA), which is responsible for air travel, disagreed, and said that flying could be unsafe. After months of arguments the two agencies hammered out a compromise this month, in which mobile networks would implement “exclusion zones” around certain airports while more studies were carried out. The airlines’ last-minute announcement suggests that deal is now off, though on January 18th Verizon and AT&T, two telecoms companies, agreed to pause turning on some wireless towers. On the same day several international airlines—including Air India, Emirates, and Air Japan—cancelled flights to several American cities, citing concerns about 5G.

Most experts sympathise with the FCC. Similar 5G networks have been deployed in dozens of other countries, and the FAA admitted in November that there had been no reports of problems. It is hard to see how comparatively low-power 5G networks could cause problems when, for instance, much more potent military search radars do not. And there is a sizeable gap on the radio-frequency spectrum between the 5G networks in question, which operate between 3.7 and 3.98Ghz, and the altimeters, which use frequencies between 4.2 and 4.4Ghz. One possible explanation comes from the fact that airlines are not threatening that all planes will be grounded—only some. Some commentators speculate that the aircraft at risk may have older, poorer-quality altimeters that are more susceptible to interference. The FAA has conceded that the cost of replacing such altimeters would be “substantial”. Battered by covid-19, airlines may be unwilling to pay.

Whatever the truth, it is rare to solve technical questions like this by publicly threatening to disable entire industries. Political intervention is likely to be needed to break the logjam. None of this is a good advertisement for America’s regulators. And it is unlikely to be the last such problem either. The radio-frequency spectrum is limited and already crowded, and demand for it is growing. Two years ago the National Oceanic and Atmospheric Administration complained that 5G deployments using a different part of the spectrum, around 24Ghz, might interfere with weather radars. Keeping everyone happy is only going to get harder.

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