The FAA has released a Special Airworthiness Information Bulletin (SAIB) that warns pilots of the risk of “potential adverse effects” on radio altimeters once 5G wireless broadband networks are deployed starting Dec. 5, 2021.
AIR-21-18 notes that the FAA is “currently collaborating” with the Federal Communications Commission (FCC) and the National Telecommunications and Information Administration (NTIA) to “assess the need for mitigation beyond the recommended action in this SAIB.”
The Potential Problem
In the United States, there has been wireless broadband deployment in the 3.65-3.7 GHz band since 2007. Starting in 2012, the FCC started looking at expanding broadband service to the 3.7-4.2 GHz range. Aviation groups, among others, complained that this could interfere with radio altimeters, which operate between 4200-4400 MHz.
The FCC moved ahead with the expansion, conducting an auction in February 2021 of the 3.7-3.98 GHz frequency band. It subsequently issued licenses to several wireless network providers.
Actual wireless broadband deployment will occur in phases, with operations beginning only in the lower 100 megahertz of the band (3700-3800 MHz) and only in 46 markets as of Dec. 5, 2021, according to the SAIB.
According to the SAIB, the FAA’s approval process for radar altimeters “does not provide criteria for compatibility with adjacent band operations, including potential impacts associated with wireless communications system deployments.”
FAA officials note they are actively participating in a committee led by the RTCA, which is developing “minimum operational performance standards for future radio altimeter designs” that are compatible with adjacent bands that include wireless networks.
RTCA is a private, not-for-profit association founded in 1935 as the Radio Technical Commission for Aeronautics. Now known simply as RTCA, its mission is to “inspire the creation and implementation of integrated performance standards that meet the changing global aviation environment and ensure the safety, security, and overall health of the aviation ecosystem.”
The FAA also is conducting a “risk assessment to ascertain whether further mitigation is warranted in addition to the recommended actions in this SAIB.”
Recommended Actions
Among the 20 recommendations in the SAIB are several directed at radio altimeter manufacturers and aircraft manufacturers to “voluntarily provide to federal authorities specific information related to altimeter design and functionality, specifics on deployment and usage of radio altimeters in aircraft, and that they test and assess their equipment in conjunction with federal authorities.”
Recommendations specifically targeted to pilots include:
- Seek information from the aircraft manufacturer and the radio altimeter manufacturer on possible effects of harmful interference due to wireless broadband deployment in the 3700-3800 MHz band and possible pilot interventions.
- Be aware of the potential degradation of radio altimeter capabilities and ways to compensate for in-flight radio altimeter anomalies.
- Remind passengers to set all portable electronic devices to a non-transmitting mode or turn them off.
- Pilots who experience radio altimeter anomalies should notify air traffic controllers as soon as practical. Reports should include as much detail as possible and include information to describe radio altimeter anomalies.
You can read the entire SAIB at FAA.gov.