New Wireless Concessions Buy More Time To Quantify 5G Aviation Safety Risks

AT&T and Verizon Wireless have agreed to limit deployment of their new 5G C-band services around some of the busiest U.S. commercial airports, acquiescing to a last-minute plea by major airlines so that aviation stakeholders can further quantify potential safety risks to radio altimeters and related systems. 

Both wireless companies said their moves are voluntary and temporary, coming on the heels of a letter signed by Airlines For America (A4A) CEO Nicholas Calio and the seven executives that head the association’s full-member airlines. The Jan. 17 letter asked the wireless companies to hold off deploying their 5G services “within the approximate 2 mi. of airport runways at affected airports as defined by the FAA.” 

Neither company would specify which airport areas are part of the agreement. A source with knowledge of the situation confirmed that the affected towers are near about 90 airports flagged by the FAA and aviation industry stakeholders as being both potentially affected by the initial 5G rollout phase and critical to the National Airspace System. The list is fluid, a second source said. 

The initial wireless rollout, set for Jan. 19, covers 46 markets in 32 states. Several markets with large airports, including Atlanta and Denver, are not part of the initial coverage area. 

Protection around many airports flagged as at risk gives aircraft and avionics manufacturers as well as the FAA more time to determine the level of risk associated with each airport and aircraft/radio altimeter combination. 

Radio altimeters, also called radar altimeters or radalts, determine an aircraft’s height above terrain. They use the 4.2-4.4 GHz frequency band of the radio spectrum. The new 5G services will eventually use 3.7-3.8 GHz, but the initial “guard band,” or gap, is 400 MHz, reducing to 220 MHz in 2023.  

U.S. aviation stakeholders are not convinced the gap combined with other 5G network technical specifications are sufficient to protect radalts from interference, so the FAA issued a series of notices to air missions (NOTAMs) effective Jan. 19 that limit low-visibility approaches to hundreds of runways at airports of all sizes and restrict some procedures. 

Airports with the 2 mi. buffer will get some relief, but the FAA and manufacturers are still working to validate specific aircraft for use at any airport flagged for possible 5G interference with as few operational restrictions as possible. Data from radalt suppliers showing protection radius will be cross-referenced with base station locations near airports to determine where aircraft can safely operate. 

Alternate Means Of Compliance

The FAA in recent days approved two Collins Aerospace radalts, the LRA-900 and LRA-2100, as being safe to operate on approaches to hundreds of potentially affected runways. Following the last-minute agreements by the wireless carriers, the agency is working to modify the two alternate means of compliance, or AMOCs, so they cover more of the affected airports with the buffer zones.  

While beneficial, the initial AMOCs are limited, applying only to low-visibility operations such as Category II and III approaches and related “automatic landing operations,” as detailed in a December 2021 airworthiness directive that established the limitations. The approvals do not cover all onboard systems that use radalt data—a list that includes traffic alert and collision avoidance systems, enhanced ground proximity warning systems, windshear detection, and stick-shaker stall-warnings.

The FAA is working on additional AMOCs that address the linked systems. 

Some affected aircraft will be subject to airworthiness directives. The 787 fleet, which is not on the Boeing AMOC issued Jan. 15 and can therefore use restricted airports only in good weather, may experience 5G C-Band-related interference with engine and braking systems during approaches. Absent an AMOC, operators must account for the possibility when landing at any airport covered in a NOTAM, according to a directive set for publication Jan. 19.

“The receiver on the radio altimeter is typically highly accurate, however it may deliver erroneous results in the presence of out-of-band radio frequency emissions from other frequency bands,” the FAA explained in the directive’s preamble. “The radio altimeter must detect faint signals reflected off the ground to measure altitude, in a manner similar to radar. Out-of-band signals could significantly degrade radio altimeter functions during critical phases of flight, if the altimeter is unable to sufficiently reject those signals.” 

Similar issues on other aircraft could leave them unusable at affected airports in any weather starting Jan 19, unless AMOCs are approved. In the interim, aircraft manufacturers are issuing recommended restrictions.  

Late on Jan. 18, the Boeing 777 was among several models facing that dilemma, industry sources told Aviation Week, but an AMOC for the venerable widebody twinjet was expected to be finalized before the rollout began. 

Late Scrambling

The uncertainty led several non-U.S. carriers, including Air India, All Nippon Airways, Emirates Airline, and Japan Air Lines to either change equipment types or cancel service on some U.S. routes starting Jan. 19. 

Meanwhile, pilots operating to affected airports are implementing new procedures. Examples are additional, precautionary pre-flight briefings and pop-up prompts on electronic flight bag screens that require pilots to scroll through reminders focusing on possible anomalies upon arrival, one airline source told Aviation Week. 

The newest chapter in the long-running 5G saga triggered another round of finger-pointing between the two industries. 

“At our sole discretion we have voluntarily agreed to temporarily defer turning on a limited number of towers around certain airport runways as we continue to work with the aviation industry and the FAA to provide further information about our 5G deployment, since they have not utilized the two years they’ve had to responsibly plan for this deployment,” AT&T said in a statement.  

Air Line Pilots Association (ALPA) President Joe DePete said the new services should not be launched near airports flagged by the FAA “until a permanent fix is found,” blaming the Federal Communications Commission for ignoring aviation’s concerns that date back to at least 2018. 

“As we have reiterated for years, the aviation community has been raising red flags about 5G interference with aircraft safety instruments—concerns that have been ignored by the Federal Communications Commission and the telecom companies, creating the mess we’re in today,” he added.