Checklist: Understanding The 5G Interference Issue

AT&T technicians install a 5G antenna system
AT&T technicians install a 5G antenna system. Credit: AT&T

The FAA and U.S. aviation industry groups are concerned that new 5G wireless networks using C-band frequency spectrum between 3.7-3.98 GHz (3700-3980 MHz) potentially could interfere with aircraft radio altimeters operating in an adjacent band at 4200-4400 MHz.

Radio altimeters, also called radar altimeters or radalts, track an aircraft’s clearance height over terrain by measuring reflected signals from about 2,500 ft. above ground level. 

The top end of the C-band 5G allocation—3980 MHz—leaves a 220 MHz buffer with the lower end of the radalt band at 4200 MHz. Experts say a number of factors could contribute to an environment where out-of-band interference is possible, including a 5G base station’s effective radiated power, antenna tilt and proximity to an airport approach path.

Background and Current Situation

FCC Commissioners in 2020
The FCC in 2020 under former Chairman Ajit Pai. The current chairwoman, Jessica Rosenworcel, is seated at far left. Credit: Federal Communications Commission

In its C-band Report and Order, adopted on Feb. 28, 2020, the Federal Communications Commission (FCC) by 3-2 vote adopted new rules “to auction and make available quickly and efficiently” 280 MHz of spectrum from 3.7-3.98 GHz for flexible use, including for 5G wireless services. “Making this critical spectrum available represents another important step to closing the digital divide, especially in rural areas, and secures U.S. leadership in 5G,” said the commission, then led by Chairman Ajit Pai, a Republican. Jessica Rosenworcel, a Democrat who now chairs the FCC, dissented, as did Commissioner Geoffrey Starks (D).

AT&T and Verizon Wireless (under the name Cellco Partnership) were among the winning bidders in FCC Auction 107, which concluded on Feb. 17, 2021, generating a record $81 billion in proceeds. Verizon was the top bidder at $45 billion, followed by AT&T at $23 billion. Among other bidders obtaining spectrum licenses through the process were T-Mobile and U.S. Cellular.

Original plans called for AT&T and Verizon to deploy their 5G C-band networks on Dec. 5, 2021. At the request of the U.S. Department of Transportation, the companies delayed their service launches by one month to Jan. 5, 2022. Under mounting pressure from a broad coalition of aerospace manufacturers, airlines, labor groups, trade associations and some U.S. lawmakers, they agreed a second time to pause the launches, which are now scheduled to begin on Jan. 19, 2022.

Under the latest agreement, announced on Jan. 3, the telecom companies have agreed to implement 5G exclusion zones around 50 priority airports identified by the FAA for a period of six months. The FAA will work to issue alternative methods of compliance (AMOCs) to its regulations for altimeter equipment and airport locations.

Alerts, Bulletins and Airworthiness Directives

Garmin radio altimeter.
A Garmin radio altimeter. Credit: Garmin

The FAA has released two airworthiness directives (AD), effective on Dec. 9, 2021, that prohibit operators of transport- and commuter-category airplanes and helicopters, respectively, from conducting certain flight operations that require radalt data when in the presence of C-band 5G wireless transmissions.

Affected operations could include instrument landing system approaches, Required Navigation Performance-Authorization Required approaches, automatic landing operations and pilots’ use of head-up displays or enhanced flight vision systems to touchdown on the runway.

The ADs require operators to revise their aircraft or rotorcraft flight manuals to prohibit operations requiring radalts in areas of 5G interference identified by Notices to Air Missions (NOTAMs), formerly called Notices to Airmen.

  • AD 2021-23-12 affects an estimated 6,834 transport- and commuter-category airplanes, according to the FAA.
  • AD 2021-23-13 affects an estimated 1,828 helicopters

The FAA will use four types of NOTAMs to identify the areas, airports and heliports where radalts and aircraft systems integrated with radalts might be unreliable: Airspace, Aerodrome, Instrument Approach Procedure (IAP) and Special IAP for private landing locations.

  • The FAA issued a Safety Alert for Operators—SAFO 21007—providing information and guidance to operators on the risk of potential adverse effects of 5G C-band wireless transmissions on radio altimeters on Dec. 23, 2021. 

The SAFO also explains the role of NOTAMs in identifying the geographic area where certain operations requiring radalt data are prohibited due to the presence of 5G C-band signals.

  • Special Airworthiness Information Bulletin (SAIB) AIR-21-18, originally issued on Nov. 2, 2021 and updated on Dec. 23, 2021, recommends reporting actions if radalt anomalies occur.

In the SAIB, the FAA asks avionics manufacturers and aircraft manufacturers and operators to voluntarily provide information on their radalt designs, functionality and usage and to test and assess their equipment in conjunction with federal regulators. 

  • The European Union Aviation Safety Agency (EASA) on Dec. 17, 2021 issued Safety Information Bulletin 2021-16, “Operations to aerodromes located in United States with potential risk of interference from 5G ground stations (as published through aerodrome NOTAMs).” 

The EASA safety bulletin is available for download at:

Bizav Associations React
Helicopter Association International: “HAI is encouraged to see the wireless carriers offer further concessions in attempt to resolve the devastating impact that 5G deployment would have on airline operations. However, the effects of 5G deployment are not limited to the nation’s busiest airports, and mitigations by wireless carriers should not be limited to those locations either. All over the country, from densely populated cities to oil rigs 200 miles offshore, helicopters are used to save lives, serve and protect American citizens, and support critical industries in demanding environments—and many of those missions are conducted from start to finish without the use of airports. 

The families of those who die because a helicopter was not able to be dispatched to the scene of an accident because it was too close to a 5G tower will not be consoled by faster Internet speeds. The loss of a single life because of misguided 5G-related policies would be reprehensible.

The voluntary measures proposed by the wireless carriers would provide modest 5G limitations at the surface of public-use heliports, of which there are only 55 in the country. That number is dwarfed by the estimated 6,533 to 8,533 helicopter air ambulance landing sites in the United States, with more than 4,000 being private-use heliports co-located at hospitals.”

NBAA President and CEO Ed Bolen: “NBAA welcomes this short-term reprieve from the Verizon and AT&T 5G rollout, so that we can better understand and communicate its potential impact on aircraft, airports and airspace across the system. We need answers to key questions in order to ensure we remain the world’s largest, safest and most efficient aviation system, and we will utilize this time to gather and share much-needed information about this development for all aviation segments, including business aviation.”

NBAA has developed an on-line resource of 5G guidance and background information at:…

National Air Transportation Association: “NATA is encouraged that the telecom companies recognize the potential effect of 5G services on the nation’s aviation infrastructure. Even this brief amount of additional time will allow stakeholders to better characterize and mitigate the impact. Recognizing the relief is temporary, discussions swiftly continue as work remains to determine a path forward,” said NATA Vice President of Regulatory Affairs John McGraw.

Aircraft Owners and Pilots Association: “We continue to work with our coalition partners to raise awareness of the safety concerns raised by experts as well as the economic impacts that disruption could impose,” said AOPA Director of Airspace, Air Traffic and Security Jim McClay. “We very much appreciate the FAA's diligence in working to protect the safety of the national airspace system. We hope that common sense will prevail so that interests on all sides are protected.”

Bill Carey

Bill covers business aviation and advanced air mobility for Aviation Week Network. A former newspaper reporter, he has also covered the airline industry, military aviation, commercial space and unmanned aircraft systems. He is the author of 'Enter The Drones, The FAA and UAVs in America,' published in 2016.


Did anyone test for interference?
There are tens of millions of people whose lives could be endangered by this 5G introduction. Putting aside that this unknown "problem" should have been solved five years ago and not made an emergency on the air transportation system, the FAA no doubt will put it on the legacy owners of radar altimeters amongst others to bear the burden of making changes rather than the newbies being required to make 5G systems compatible. Since there is technically no overlap of the frequencies involved then the obvious solution is for the FCC to tighten the frequency requirements on 5G to make certain that no overlap occurs.
If 5G is potentially the culprit then 5G needs to be fixed and only the FCC can require that. I cannot fathom for a moment why the FCC's vote on 5G was along party lines. I have a feeling this problem has a political component that does not bode well for aviation. 100 billion dollars for licenses is where the problem begins and ends.
It is interesting that none of the articles clearly states who is at fault. Is the 5G mobile signal bleeding into the radio altimeter range or is it the radio altimeters that need a filter to stay out of the 5G range?
Figure 3.1, "Spectrum Illustration Showing 5G Fundamental and Spurious Emissions," from page 6 of "Assessment of C-Band Mobile Telecommunications Interference Impact on Low Range Radar Altimeter Operations", (RTCA Paper No. 274-20/PMC-2073), dated October 7, 2020, looks to me like a confession of guilt by the aviation industry. It plainly states (green lines and text) that "typical" radar altimeters accept signals from hundreds of megahertz outside their band allocation (4200-4400 MHz). Apparently until 5G came along, there was nothing near the radar altimeter channel allocation, so some manufacturers took little precaution to limit their device's response to out-of-band signals. Then 5G shows up, and some commercial aircraft have susceptible radar altimeters. Doesn't sound like the problem is with 5G, but with obfuscation and foot-dragging by the aviation industry.
It would seem the attitude of the FCC, Verizon, AT&T and the bags of cash that touch the sky are completely indifferent to the problems of the FAA, and the clear potential to threaten human life and disrupt a pivotal industry. Their approach appears to be one of, "We got our stacks, so why don't you go figure it out."