A plan to redeploy spectrum for super-fast 5G wireless networks is sparking concern among aviation safety experts that it could result in interference with the electronics on aircraft, potentially leading to crashes.

The U.S. Federal Communications Commission is scheduled to begin an auction on Tuesday for airwaves in the so-called C-band frequencies that are used by satellite providers but the agency wants to re-assign for 5G. The agency says the sale is an important step in maintaining U.S. leadership in the next generation of wireless service.

But some fear that assigning the frequencies to ground transmitters near airports that will be used for 5G networks could interfere with electronics used by aircraft as they land.

“I see a very significant safety issue here unless we find a way to mitigate it,” said Terry McVenes, president of RTCA Inc., a Washington-based nonprofit that studies technical issues involving aviation.

The FCC says there’s enough of a buffer between the spectrum used by 5G and the altimeters aboard aircraft for them to safely co-exist. “We continue to have no reason to believe that 5G operations in the C-band will cause harmful interference,” said FCC spokesman Will Wiquist.

But the RTCA, formerly known as the Radio Technical Commission for Aeronautics, produced a 217-page study laying out potential hazards, including the potential for planes to crash near airports such as Chicago’s O’Hare International.

“It takes a lot to wind me up,” said McVenes, a former safety chief for the Air Line Pilots Association. “If left to go the way it is, our data shows very serious problems.”

McVenes didn’t recommend what steps should be taken to mitigate the problem, and said a solution might emerge from more talks with the communications industry. He said it would take years to design and replace altimeters.

Airlines for America, a trade group for large U.S. carriers, said it “appreciates the RTCA’s findings.”

“We encourage the FCC to reassess and better understand the interference risks associated with their proposal and make sure safety-critical aviation systems will continue to be protected,” the trade group said in a statement.

A coalition of 15 aviation-industry groups representing airline pilots, private business-jet operators and cargo carriers sent a letter to the FCC on Monday, saying they’d been raising concerns since 2017 and asking the agency to suspend the auction.

Moving ahead “would be a disservice to the safety of the traveling public and put our nation’s airlines, business and general aviation, and helicopter operations at risk,” the group said in the letter.

The U.S. Federal Aviation Administration says it is concerned about potential interference with altimeters “and is working closely with our interagency partners at the National Telecommunications and Information Administration and the Federal Communications Commission on this important issue.”

Aviation regulators in France have gone further and have slowed the deployment of 5G around airports while they study the matter.

The dispute comes as the FCC prepares for an auction that’s something of a capstone for Chairman Ajit Pai. The Republican, who is leaving office in January, has made it a priority over his four years as chairman to reassign frequencies from long-established communications to mobile uses.

Under Pai’s guidance satellite providers such as Intelsat SA and SES SA agreed to give up the C-band frequencies and operate in a smaller swath. In return they are to receive a portion of the billions of dollars expected to be bid for them by mobile providers such as Verizon Communications Inc. and AT&T Inc.

The sale would dedicate a large chunk of airwaves considered particularly suitable to 5G operations, ones that travel far and can carry rich information streams. That makes them useful for the lightning-fast “internet of things” coming to factories, offices, homes, farms, roadways and airports.

‘Important Milestone’

The auction is an “important milestone,” Meredith Attwell Baker, president of the CTIA trade group representing carriers, said in an Aug. 6 blog post. “Promoting American leadership in 5G is a national priority, and keeping the C-Band auction on schedule is critical to making sure we have the mid-band spectrum we need to lead the emerging 5G economy.”

The FCC considers the auction, which begins Tuesday and could last for weeks, to be “a very important event for American consumers and U.S. leadership in 5G,” Wiquist, the agency spokesman, said. “The FCC is paving the way for Americans to receive fast 5G wireless services.”

The airwaves to be reassigned, however, are near in frequency to those used by radar altimeters—devices that calculate an aircraft’s height above the ground. According to the RTCA study, 5G signals from base stations on the ground would confound the altimeters during crucial phases of landing, when commercial aircraft are descending at 600 to 800 feet each minute.

“It just creates these totally inaccurate signals,” McVenes said. “It would do it any time the airplane went into the area where the 5G signal was happening. It would happen pretty much every time.”

For its report, RTCA plotted the landing approach to Chicago O’Hare’s Runway 27L, the most-used for arrivals. The group analyzed the effect on altimeters if existing telecommunications base stations below the incoming aircraft were converted to the new 5G signals.

Catastrophic Effects

It found “significant impacts throughout the approach with the potential for catastrophic effects.”

The result could be altimeter failures, including one like the fault that doomed a Turkish Airlines that crashed and killed nine people near Amsterdam in 2009, according to the report. In that crash the altimeter erroneously concluded the Boeing Co. 737-800 had reached ground level and the plane’s equipment automatically reduced engine thrust. Pilots didn’t notice and the jet plunged into a field.

The issue also raises safety concerns with helicopters, which operate at low altitudes where the radar altimeters are critical. The U.S. National Transportation Safety Board has cited issues with the altimeters in several copter crashes.

The FCC and CTIA have asserted that interference isn’t likely because there is plenty of buffer between the envisioned 5G uses and the airwaves assigned to the altimeters.

The RTCA’s study was “severely lacking” and reached “unsupported” conclusions, CTIA, with members including AT&T and Verizon, said in a filing.

“The test criteria that aviation created is more exacting than existing altimeter standards, and some tested altimeters, operating to manufacturer specifications, would not pass even without any external C-Band operations present,” CTIA said in a Nov. 17 filing.

Study Disputed

In a statement, CTIA said the FCC had concluded there’s no issue with “well-designed” aeronautical equipment. “Nothing in RTCA’s report changes that determination,” CTIA said.

The FCC concurred.

The U.S. plan for the airwaves offers more separation between altimeters and 5G than is the case in some other countries, Wiquist said. He cited CTIA’s concerns with the RTCA study and said, “the commission’s experts have concerns with this study as well.”

French regulators are on a different tack. The country’s aviation authority, DGAC, has told operators to slow mobile 5G deployment while it reviews its impact on aerial navigation. The delay has affected the start of 5G deployments around Nice airport and Paris-Charles de Gaulle, north of the capital. The DGAC consulted the RTCA report for its study, which continues.

The FCC in its February order establishing the auction called for a working group that included telecommunications and aviation experts to examine the altimeter issue. Meetings began in May, but the group ceased operating in November after its members failed to reach consensus and decided more talks wouldn’t serve a useful purpose.

The FCC in the February order said it expects the aviation industry “take appropriate action, if necessary, to ensure protection” of electronic devices.

Mitigation might include new altimeter designs and changes to 5G base stations, Lee Nguyen, an FAA official, said in a comment appended to the RTCA report. Nguyen was among three dozen aviation-industry representatives who joined the committee that issued the report.

McVenes said it would take years to design and replace altimeters.

“I’m not against 5G. I want 5G out there so my cell phone has more capability,” McVenes said. “We just wanted to make sure they did it safely.”