Over a dozen commercial aviation groups warned in the week leading up to an auction of part of the C-band electromagnetic spectrum that, as one study stated, selling could result in 'catastrophic failures' with the potential for 'multiple deaths.' By Dec. 8, The Federal Communications Commission began the auction.

The aviation groups are worried that 5G spectrum operations sold by the FCC could cause interference which would provide imprecise altimeter readings.

According to a memo received by Defense News, the President of the Federal Aviation Administration and #2 at the Transportation Department expressed these fears and are calling on the FCC to delay the sale to research the safety issue more closely. The FCC, in particular, has said that its own technological tests entail little to no risk and plans to proceed.

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Meantwhile, the Pentagon has not yet assessed the effect of combat aircraft and has not formalized a position on selling. The Defense Department is already grappling with the auction in progress to keep up. The Defense Department and other agencies met on December 21 to "discuss findings and develop a way forward" Honeywell Industries, a major maker of radar altimeters, will consider potential solutions from that meeting.

The warnings by detractors are loud and clear: "There will be accidents, property will be destroyed and people will die," an official says.

“The results of the study performed clearly indicate that this risk is widespread and has the potential for broad impacts to aviation operations in the United States, including the possibility of catastrophic failures leading to multiple fatalities, in the absence of appropriate mitigations,” said the RTCA, a private company partnering with the FAA to establish standards of safety

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The C-3.7–3.98 band's GHz frequency component at present is comparatively silent, mostly protected by low powered satellites. Once 5G telecommunications in the 3.7-3.98 portion of the band have been developed, there is a "significant danger" of "harmful interference"

“These RTCA findings are alarming; they not only align with earlier research identifying harmful effects of 5G networks to radio altimeters, but they reflect a clear need for the FCC to return to the drawing board with this premature plan,” said Rep. Peter DeFazio, the Oregon Democrat who leads the House committee in a letter to FCC Chairman Ajit Pai on Dec 7, “There is no question that additional study is needed to understand the full extent and severity of 5G interference with radio altimeters and whether any mitigations are feasible — or even possible — to ensure flight safety."

“We must never take a chance with aviation safety — and at no point should commercial interests be placed above it.”

The FCC and the expanding 5G backers claim that the fears are unfounded.

The transport airplanes and air-borne refueling tankers run by the Air Mobility Command of the Air Force will be more impeded by intervention by 5G due to their similarity in comparison to commercial aircraft.

For military planes, low flying trips over land like mountains will be the biggest problem. When flying above the ground, fighter pilots use their radar altimeters to stop enemy radars or surface-to-air attacks. Holmes noticed, however, that not all combat jets, including the F-15C era of the 1970s, had radar altimeters, and pilots could still rely on visual indicators.

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In the C-Band Order, the Commission concluded that our rules would protect radio altimeters used by aircraft, and we continue to have no reason to believe that 5G operations in the C-Band will cause harmful interference to radio altimeters, among other things, these altimeters operate with more than 200 megahertz of separation from the C-band spectrum to be auctioned, more protection than is afforded in some other countries."
"Moreover, the RTCA report was prepared outside of the joint aviation/wireless industry group that was set up at the Commission’s request and is not a consensus position of that group. Indeed, at least one other member of that multi-stakeholder group has expressed significant concerns with the study and several of its assumptions, and the Commission’s experts have concerns with this study as well."

—Will Wiquist, a spokesman for the FCC in a statement

It takes time and funding to replace or adjust altimeters, Holmes says. Defense analysts are forecasting that this quantity will be short in the coming years. The military must give up manpower, time and productivity to solve the dilemma, he says. One source cited the cost of replacing "float altimeters" at "several billion dollars at a low estimate."