FAA Says Thousands of Boeing 737s Are Susceptible to 5G Interference

Regulatory wrangling earlier this year threatened to scuttle the much-anticipated rollout of new 5G networks from AT&T and Verizon. However, the carriers and US aviation officials were able to come to an agreement about how and where the new c-band spectrum could operate. Now, the FAA has issued an airworthiness directive aimed at the Boeing 737 that sheds some light on the issues that have delayed a full c-band rollout. According to the document, these aircraft could suffer altimeter malfunctions in the presence of certain 5G frequencies.

This mess could have been avoided, but it seems no one took responsibility for ensuring airlines made several necessary upgrades. The Federal Communications Commission announced in 2020 that it planned to auction off spectrum that was previously used for satellite TV operations. Now that the c-band (a block of spectrum around 4 GHz) is in the hands of carriers, it will broadcast at much higher power around the country. That’s good for your mobile data but bad for older radio altimeters.

The FCC built in a buffer zone to prevent the c-band from leaking into the spectrum reserved for air traffic. However, many older aircraft needed upgrades from their old, inefficient altimeters to prevent interference. That didn’t happen on time, and so the FAA stepped in to make sure 5G didn’t pose an immediate danger to travelers. The new directive (PDF) singles out Boeing’s 737 as a major issue for 5G. This is an extremely popular model, and the systems in many of them will not operate correctly in the presence of 5G in the 3.7-3.98 GHz range.

Radio altimeters are part of the automated landing systems on many modern planes—they’re not restricted to the 737. Interference like the FAA has identified can cause failures in the “autopilot flight director system, autothrottle system, flight controls, flight instruments, traffic alert and collision avoidance system (TCAS), ground proximity warning system (GPWS), and configuration warnings.” The agency says this could cause an unacceptable increase in “flight crew workload.” That seems like a gentle way of saying 5G could affect safety.

The notice affects 2,442 planes in the US and another 8,342 worldwide. There’s no immediate danger, though. The directive does not require the grounding of any aircraft, but it could complicate carrier efforts to roll out more 5G. The aircraft are free to continue operating in areas where 5G has been mitigated as required by regulators or where it doesn’t exist yet. AT&T and Verizon have agreed to keep c-band clear of airports and to operate at lower power levels in the surrounding area. The carriers agreed to keep things like this until the summer, at which time there will probably be another round of recriminations.