When aircraft descend safely through cloud layers, they rely on more than just pilot skill. The precision of radio altimeters—devices that measure altitude using radio waves—plays a crucial role. However, as 5G technology rapidly expands, a potential threat emerges: wireless broadband networks interfering with these critical aviation instruments.
The Federal Aviation Administration (FAA) recently issued a Special Airworthiness Information Bulletin (SAIB) highlighting this concern, urging the aviation industry to remain vigilant and collaborate on solutions.
FAA's Warning: C-Band Deployment Continues
The SAIB clearly states that wireless broadband deployment in the 3.7-3.98 GHz frequency range (C-band) continues across the United States. Since January 2022, this deployment has been implemented in phases, affecting operations throughout the contiguous U.S. The FAA's warning reflects serious risk assessment rather than alarmism.
Global Trends: 3GHz Spectrum for Mobile Broadband
Globally, the 3GHz spectrum has become a focal point for mobile broadband development. The International Telecommunication Union (ITU) and regional organizations actively promote spectrum harmonization in this range. Many countries have already allocated spectrum for wireless deployment, with more following suit. While some nations implemented temporary technical, regulatory, and operational measures—such as distance and power limitations for wireless broadband in the 3.7-4.2 GHz range—no conclusive evidence yet shows harmful interference from international wireless broadband operations.
U.S. Experience: 3.65-3.7 GHz Deployment
The United States began deploying wireless broadband in the 3.65-3.7 GHz range as early as 2007. The Federal Communications Commission (FCC) initiated procedures in December 2012 to authorize mobile broadband services in the 3.55-3.7 GHz band, finalizing rules in April 2015 and October 2018. Commercial deployment launched in September 2019, with no known altimeter issues reported since.
FCC Actions: Planning for 3.7-4.2 GHz
For the 3.7-4.2 GHz range, the FCC began soliciting input about introducing mobile broadband in 2017. The March 2018 Mobile NOW Act directed the FCC to assess commercial wireless deployment feasibility in this spectrum. The FCC initiated proceedings in May 2018 and adopted the C-band Report and Order in March 2020, authorizing flexible use of the 3.7-3.98 GHz band. After completing spectrum auctions in February 2021, the FCC issued licenses to multiple wireless providers with specific deployment timelines and parameters.
Radio Altimeter Operations and FAA Certification
Radio altimeters operate in the 4.2-4.4 GHz range. Current FAA approval processes for radar altimeters follow Technical Standard Order TSO-C87A, which lacks compatibility standards for adjacent spectrum operations. RTCA—a nonprofit aviation standards organization—established a working group to assess potential interference from 3.7-3.98 GHz wireless broadband on radio altimeters.
FAA Risk Assessment and Airworthiness Directives
The FAA conducted risk assessments to determine whether additional mitigation measures beyond those recommended in the SAIB might be necessary. Based on these evaluations, the FAA issued Airworthiness Directives (ADs) addressing potential 5G C-band interference effects on certain aircraft and helicopters equipped with radio altimeters.
Industry Recommendations
For Radio Altimeter Manufacturers:
- Submit receiver RF selectivity data, interference tolerance templates, and operational specifications for each model
- Complete analysis or testing to determine interference susceptibility across relevant frequency bands
- Report instances of altimeter performance errors
- Collaborate with aircraft manufacturers on potential design changes
For Aircraft Manufacturers:
- Submit information about installed radio altimeter models
- Communicate with suppliers to assess equipment vulnerability
- Conduct testing on potential interference effects
- Evaluate impacts across different aircraft types
For Operators and Pilots:
- Review relevant regulations and safety management systems
- Remind passengers about electronic device policies
- Seek information about potential interference effects
- Understand potential altimeter performance degradation
- Report any altimeter anomalies
Conclusion: A Shared Responsibility
The FAA's SAIB represents more than an informational notice—it serves as a call to action for the aviation industry. As 5G technology advances, collaboration among radio altimeter manufacturers, aircraft manufacturers, operators, and pilots becomes essential to maintain aviation safety. Only through continued information sharing, technological innovation, and close cooperation can the industry safely embrace technological progress while ensuring reliable flight operations.