New Safety-Zone Calculations, Flight Tests Mark 5G Progress

5G tower
Credit: Bill Oxford / Getty Images

WASHINGTON—Revamped runway safety zone parameters and a just-launched flight-test program are seen as keys to establishing both short-term and permanent fixes to the 5G wireless challenges facing aviation and telecommunications companies, executives in both industries believe. 

The FAA in recent days introduced a new method for calculating safe zones around runways affected by new 5G “C-band” services introduced by AT&T and Verizon Wireless. Granular data on wireless transmitter installations is helping the agency re-work the so-called buffer zones, or protected areas, around runways, that ensure 5G signals do not interfere with radio altimeters (radalts) that calculate altitude.  

“We have already refined our safety model, which creates essentially a safety zone and a performance buffer for radio altimeters around airports,” FAA Administrator Steve Dickson said during a Feb. 3 hearing before the U.S. House aviation subcommittee. 

The original safety buffers relied on circles around runway ends that incorporated space alongside runways that did not need protection. The revised, two-dimensional buffer zones are made up of two parts, sources with knowledge of the arrangement told Aviation Week.  

Rectangles that are 1.25 nm wide and extend 2 nm from each runway end form a runway safety zone. Beyond this core protection area, each runway has an additional “performance buffer” that is sized based on several factors, including airport geometry as well as data provided by the carriers such as specific tower locations and specifications.  

The FAA is calculating the new safety zones based on a verbal agreement between the wireless carriers and the agency that limits full deployment of certain parts of their networks until early July. The new, site-specific data is helping the FAA narrow the amount of coverage needed around some airports, which means more 5G sites can be turned on before the voluntary agreement is up. 

Flight Tests

Concurrently, the FAA has begun flight tests using its aircraft at several airports in the new 5G zones to quantify potential radalt interference risk. Results from the tests could help the FAA shrink the buffer zones even more, or reduce the radius designated around each aircraft as part of exemptions, or alternative means of compliance (AMOCs), issued to permit their operations into certain airports with possible 5G interference. They also could help the agency develop new radalt standards—a process that would likely take at least several years. 

“We have designed those flights in conjunction with the telecommunications industry engineers—their engineers are actually on board FAA aircraft—to report all the parameters of what the signal looks like as it impacts the airplane in various performance scenarios,” said Dickson, the only government official to accept the subcommittee’s invitation to testify. “As we get the data, that will help us to sharpen our analysis” of current buffer-zone needs. “It’ll also inform the performance requirements for modifications to radio altimeters or the new performance standards for retrofit equipment if that becomes necessary,” he added. 

“There will probably be some airplanes that will have to retrofit new equipment,” Dickson continued. “At a minimum, I think we will see significant retrofit of filtering devices.” 

Dickson did not discuss any of the test results, nor did he touch on reports of possible 5G interference. But the FAA has confirmed that it is investigating more than 100 reports of possible interference filed by pilots in recent weeks. Bloomberg first reported the issues.

Retrofits or new radalts are not yet a certainty. But the head of the largest wireless industry trade association suggested that funding for such initiatives could be covered by funds from the $80 billion in proceeds the U.S. government took in during the C-band auction that set the stage for the new services. 

“There have been all sorts of instances where, through a special Spectrum Relocation Fund or through a designation from Congress, there has been use” of spectrum-auction process, said Meredith Attwell Baker, president and CEO of CTIA. “Congress can use the proceeds ... as they wish. That part’s really up to the government.” 

Near-term, constantly shifting variables present the largest challenges. The Jan. 19 go-live date for the new 5G services marked the beginning of the network rollout. Even factoring in the transmitters that are part of the six-month handshake deal, both carriers are slowly adding 5G in 32 states covered in the initial network. As each location powers up, the FAA must factor in new data—information that often is not available until weeks or days before the transmitter goes online.  

Mobile units, or cell on wheels (COWs), deployed by wireless providers to boost capacity during events with large crowds present another potential challenge. Both AT&T and Verizon Wireless use COWs in a variety of ways, including downtown events near airports, and in some cases, at air shows. If a wireless provider wants to deploy a COW at or near an airport, the FAA may step in and seek to limit its 5G capability. 

While the FAA has made progress on AMOCs in the last week or so, the remaining share of the commercial airline fleet with limited or no approvals guarantees uncertainty, if not disruptions, for affected operators. The FAA’s latest information shows all mainline passenger Airbus and Boeing aircraft have broad AMOCs, as do the most common ATR models and the Mitsubishi (Bombardier) CRJs and De Havilland Dash 8-400s. All must be reviewed for renewal on a regular basis. 

Several models, including the 737 MAX, 777 and 787, are subject to added restrictions based on functions such as thrust-reverser deployment that rely on radalt data. The Embraer ERJ-135/145 series remains shut out, while the E170-series AMOC approvals contain significant restrictions or are shut out of major airports. 

Continuing Disruptions

Data compiled by the Regional Airline Association (RAA) shows that more than 25% of January’s scheduled flights at the New York City area’s three major airports—John F. Kennedy, New York LaGuardia, and Newark Liberty—were scheduled on aircraft that do not have approval to operate into them during low-visibility conditions. Smaller airports have even higher percentages, the association added. 

“Leaving dozens of airports and millions of passengers vulnerable to sweeping disruptions is unsustainable and unacceptable,” RAA President Faye Malarkey Black told lawmakers. “Today’s patchwork of [airport approvals] and airport-specific AMOCs that exclude regional aircraft is creating a two-tiered national aviation system where communities that rely on regional airline service are disadvantaged and subject to more disruption, while those served exclusively by larger aircraft are less vulnerable.” 

Cathryn Stephens, airport director at Oregon’s Eugene Airport and an American Association of Airport Executives board member, echoed Black’s stance. 

“If the FAA’s flight restrictions had been in place in 2021, conservatively there would have been about 90 low-visibility days impacting up to 40% of our flights per day,” she told lawmakers. “We would have projected similar disruptions this year without the issuance of the AMOCs. But with those AMOCs under monthly review and anticipating additional disruptions as the next rounds of 5G C-Band rollout, we know there will be additional disruptions if no action is taken to immediately and safely return additional regional aircraft to service.” 

Stephens urged the FAA to continue development of “narrowly tailored and sufficiently sized” zones at “all affected airports” while continuing to explore ways to expand aircraft approvals. 

Sean Broderick

Senior Air Transport & Safety Editor Sean Broderick covers aviation safety, MRO, and the airline business from Aviation Week Network's Washington, D.C. office.