In January, at least three flights simultaneously suffered altimeter errors over Tennessee that caused them to “be unable to maintain their designated altitude,” one pilot said. One jet reportedly lost its autopilot entirely and fire engines were on standby when it landed.
In February, a passenger plane attempting to land at Louis Armstrong International Airport in New Orleans experienced erratic low-altitude warnings while flying below 1,000 ft. “Such false warning indications would be extremely distracting in more challenging environments, such as poor visibility or icing conditions,” the pilot later wrote.
In March, a commercial jet was landing on autopilot at Los Angeles International Airport when it suddenly began to plummet just 100 feet above the ground. “I took control of the plane and landed with the nose up,” the pilot reported. “It was a very scary error on the autopilot. [other] Depending on the circumstances, this could have led to a collision.”
Pilots blame those three accidents, and many more this year, on problems with the plane’s radio (radar) altimeter, which pilots rely on during takeoff and landing and to avoid crashing into mountains, and which also affects critical autopilot, autothrottle and instrument landing systems. IEEE Spectrum An analysis of reports submitted to NASA’s Aviation Safety Reporting System (ASRS) found that complaints about malfunctioning or failing altimeters have skyrocketed since the deployment earlier this year of high-speed 5G wireless networks that use similar frequencies.
ASRS is a public database maintained by NASA that encourages U.S.-based air and ground crews and air traffic controllers to anonymously share safety incidents and concerns. Between January and May, there were 93 reports of radar altimeter malfunctions or failures, compared to just a handful in a typical year. In January alone, there were nearly double the number of complaints about altimeter malfunctions than in the previous five years combined. In most incidents, including the Tennessee and Los Angeles incidents mentioned above, reporters cited 5G interference.
The Federal Communications Commission initially downplayed concerns that new cell phone towers and equipment could interfere with commercial jet radar altimeters that operate hundreds of megahertz higher in the radio spectrum. In early 2020, the commission wrote: “The technical rules for power and radiation limits in the 3.7 GHz band exceed the limitations of this technology.” [gigahertz] The service and 220 megahertz of spectral isolation provide significant protection for services in the 4.2-4.4 GHz band.”
The US FAA wasn’t so sure. It commissioned an empirical study from RTCA, a nonprofit that researches avionics, to assess the operational risks of 5G interference. The report concluded that C-band 5G systems would cause harmful interference to radar altimeters on all types of commercial aircraft, saying, “The risks are pervasive and could have far-reaching effects on US aviation operations, including the potential for catastrophic failures resulting in multiple fatalities.”
The report concluded that risks arising from deliberately false signals from mobile phone towers on the ground, and from misoperated 5G mobile phones on aircraft, could be exacerbated by altimeter receivers with poor spectral selectivity. In what now seems prescient, the RTCA report stated:[The] The potential for harmful interference… is particularly dangerous given that, to date, radar altimeter failures have been extremely rare.”
The spectrum auction took place anyway, and wireless carriers led by Verizon and AT&T paid more than $80 billion for spectrum. 5G service was scheduled to launch in 46 US markets on January 5th of this year. But as the launch drew near, the FAA issued an airworthiness directive that significantly restricted air travel to those areas.
Ultimately, wireless carriers agreed to delay 5G rollout for two weeks, and the FAA banned certain aircraft with susceptible or untested altimeters from low-visibility landings at airports with 5G wireless networks. The networks also agreed to establish “buffer zones” around 50 airports that will reduce 5G C-band signal levels by at least 10 times within one mile of takeoff and landing runways. The mitigation measures are expected to be in place for six months while the FAA works to get more aircraft approved to operate.
The 5G system went live on January 19th.
Almost immediately, complaints started coming in to NASA. On the first flight to San Francisco since 5G was turned on, one pilot got a scare when the plane’s speed brakes unexpectedly activated before landing. “In over 18,000 hours as a Boeing passenger aircraft captain, I have never experienced an automatic speed brake unexpectedly activated prior to ground contact,” the pilot wrote. “While I operate in a 5G environment, I do not intend to perform my first 5G landing.”
“I was surprised that an actual interference event occurred because I assumed this would be a no-brainer,” said another pilot, who suspected an altimeter malfunction may have caused the plane’s autothrottle to disengage.
The ASRS included at least 40 reports of possible 5G interference around 50 airports with buffer zones, with Phoenix Sky Harbor International Airport receiving the most complaints, with six reports.
“I’ve been flying planes with radar altimeters for years and have never seen a glitch like this until 5G was turned on,” wrote another pilot in Florida, whose altimeter fluctuated between minus 90 feet and 400 feet before takeoff. “Coincidence? Probably not.”
But is that true? “I would sleep like a baby,” said Chris Rudell, an associate professor in the Department of Electrical and Computer Engineering at the University of Washington. [on a plane] “We flew over a 5G tower at full power,” he said. spectrum“Maybe something unusual happens and the pilot blames it on 5G, but maybe it’s not 5G’s fault. After all the coverage in the news, pilots are now willing to submit what they actually saw, whereas before they may not have been willing to do so.”
Indeed, the FAA now has an online reporting form for radio altimeter anomalies that pilots and other aviation professionals are asked to fill out. The agency did not release details about those reports but did provide summary data indicating it has received about 550 reports since January.
The agency reviewed more than half of the reports but could not rule out the possibility of 5G interference in about 80 of the accidents. In contrast to the ASRS report, none of the interference events identified by the FAA affected safety-related systems that affect direct aircraft control inputs, such as autothrottles or speed brakes. The FAA concluded that the mitigation measures it agreed to with wireless carriers are “working.” In June, it reached an agreement with the carriers to extend those mitigation measures for another year.
While complaints about ASRS altimeters appear to be declining, many pilots still want stricter controls on 5G technology. AOPA, the world’s largest organization representing general aviation pilots and aircraft owners, said: spectrum“We call for continued consultations between the public and private sectors to further mitigate the security risks posed by 5G technology to radar altimeters. Further cooperation and coordination will lead to solutions that work for everyone.”
Some pilots, speaking anonymously, were less diplomatic. [sic] “5G shouldn’t be deployed until it’s been carefully tested,” one person suggested. “Delay the rollout of 5G service until all the issues with radar altimeters and transport aircraft are resolved,” another wrote. A third simply pleaded, “Turn off 5G cell service near airports.”
This article has been updated to clarify AOPA’s status as an aviation association.
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