Radio altimeters (sometimes called radar altimeters) measure an aircraft’s height above the ground and feed that data to pilots and multiple onboard safety systems. The FAA says the upgraded (“next-generation”) altimeters must be able to withstand interference from wireless signals in neighbouring spectrum bands and continue producing accurate readings. By Oct. 31, 2034: All other aircraft with radio altimeters that must comply with Part 91 (including aircraft operating under Parts 125, 133, 135, 136, 137, 194, and other Part 129 aircraft not in the first group). The FAA ties the rule directly to federal spectrum policy. The FAA emphasises that radio altimeters are critical safety equipment, especially for low-visibility takeoffs and landings, and that inaccurate readings can ripple into multiple aircraft safety functions.