The One Big Beautiful Bill Act of 2025 requires the Federal Communications Commission (FCC) to auction at least 100 megahertz of spectrum in the Upper C-Band (3.98-4.2 GHz) immediately adjacent to the radio altimeter spectrum band (4.2-4.4 GHz), as the Trump administration seeks to solidify U.S. leadership in fifth-generation wireless services, optimize spectrum utilization, and support commercial innovation. To ensure safety, efficiency, and reliability of aviation operations in the presence of wireless signals in the Upper C-Band, the Federal Aviation Administration (FAA) is proposing new regulations which would require all radio altimeters to meet specific minimum performance requirements. These new radio altimeters must withstand interference from high-powered wireless transmissions in neighboring spectrum bands and continue to provide accurate altitude readings to both pilots and integrated aircraft safety systems. The minimum interference tolerance requirements proposed in this rule are based on the latest proposal from the industry consensus body which is developing a comprehensive standard. These regulations would require all aircraft equipped with radio altimeters operating under part 121 and those aircraft operating under part 129 with 30 or more passenger seats or a payload capacity of more than 7,500 pounds to comply with the minimum performance requirements by the date the Federal Communications Commission authorizes transmissions in the Upper C-Band. All other aircraft equipped with radio altimeters would be required to comply with the same minimum performance requirements two years later. This proposed rule is a companion to the Federal Communications Commission Notice of Proposed Rulemaking to expand flexible use of additional spectrum in the Upper C-Band in support of the required auction.