The FAA's 5G Radio Altimeter Mandate and the C-Band Auction That Forces the Fix

The FAA will issue a final rule on July 24, 2026 requiring all affected aircraft to be fitted with radio altimeters that can tolerate 5G interference in the C-band, according to reporting from AeroTime. The rule makes permanent a fix that has been phased in since 2021, and it arrives at the same moment the FCC clears the way for wireless carriers to use their C-band spectrum at full strength. If your aircraft has a radio altimeter in the panel, this rule applies to you.

What the FAA Final Rule Actually Does

The rule formalizes years of temporary measures into a permanent standard. From now on, a radio altimeter in the affected fleet must reject out-of-band 5G signals sharply enough to keep working even with a 5G tower lit up right off the approach end of the runway.

In exchange, the temporary buffer zones and voluntary power limits that carriers accepted near airports are ending. The carriers get full-strength use of the spectrum they paid for, and the fleet has to be genuinely immune to it.

That is the trade at the center of this story: permanent spectrum access for the phone companies, permanent interference tolerance for the airplanes.

Why This Fight Started: The 2021 C-Band Auction

Go back to 2021, when the Federal Communications Commission (FCC) auctioned a large slice of C-band spectrum to wireless carriers to build out fast 5G service. The auctioned spectrum sits between 3.7 and 3.98 GHz, and the sale pulled in tens of billions of dollars.

Aviation got nervous because the radio altimeter - the device that reports your height above the ground during the final phase of an approach - operates from 4.2 to 4.4 GHz.

Compare the two: the 5G band tops out near 3.98 GHz, and the altimeter band starts at 4.2 GHz. That leaves a guard band of roughly 200 MHz between them.

To many engineers, that gap sounded like plenty of room. To the FAA and the radio altimeter community, it did not. The worry was that older altimeters - some designs flying for decades - used receivers that weren’t very selective. They listened to a wider slice of spectrum than they needed, and a powerful 5G transmitter near a runway could bleed energy into that receiver.

Why the Radio Altimeter Matters So Much

The radio altimeter is not just a number you glance at. It feeds the automated systems that fly the airplane down to the pavement.

On transport category aircraft, the altimeter feeds the autoland system, the terrain awareness and warning system (TAWS), and the auto-throttle retard near touchdown. On many aircraft it drives the flare cues. And during a Category II or Category III approach in low visibility, that height reading is the difference between a safe landing and a very bad day.

An altimeter fooled by interference could report the wrong height, or flag itself as failed and drop you out of autoland capability at the exact moment you need it. That is the safety case that drove the FAA to act.

How the Situation Unfolded, 2022 to 2024

The fix arrived in stages, not all at once.

When carriers were ready to switch on C-band service in early 2022, the FAA and airlines pushed back hard, fearing mass cancellations and diversions at major airports. The carriers agreed to voluntary mitigations - powering down or adjusting transmitters near dozens of key airports and creating buffer zones around runways. That bought time, but everyone understood it was a bridge, not a destination.

Through 2023, the FAA issued airworthiness directives (ADs). Operators had to identify which altimeters were vulnerable, and the agency restricted certain low-visibility operations at airports with active 5G, using notices to airmen (NOTAMs) to warn crews when an approach couldn’t be flown to the lowest minimums.

Critically, the agency set a deadline: operators of transport category airplanes were told to retrofit or replace vulnerable radio altimeters with filtered, tolerant units by early 2024. Meanwhile, altimeter manufacturers and the wireless industry worked out standards defining exactly how sharply a compliant unit must reject signals outside its band.

Who This Rule Actually Affects

The heart of the rule targets transport category aircraft - airliners and business jets flying into the fog at major airports.

If you fly Part 121 for an airline, or you fly a turbine airplane with autoland and low-visibility capability, your operation has almost certainly already handled this. Your maintenance shop has been tracking the ADs, and your altimeters have likely already been upgraded or swapped.

But the general aviation crowd should not assume this doesn’t reach them. Plenty of light aircraft now carry radio altimeters - turboprops, high-end piston twins, and even some well-equipped singles with modern avionics suites. If there’s a radio altimeter in your panel, you are inside the tent, and you need to know whether your unit is a tolerant design or a legacy unit on the watch list.

What Pilots Should Do About It

First, confirm whether your airplane even has a radio altimeter. It is distinct from your barometric and encoding altimeters. The radio altimeter - sometimes called a radar altimeter - bounces a signal off the ground and typically reads out only in the last couple thousand feet. If you have one, know its make and model.

Second, talk to your avionics shop or maintenance provider directly. Ask whether your radio altimeter is compliant with the 5G tolerance standard, and whether an airworthiness directive applies to your tail number. They can cross-reference your unit against the FAA’s list.

Third, read the applicability section when the final rule publishes. That section spells out which aircraft and operations are covered, and by when. Don’t act on the headline alone - and don’t panic on it either. If there’s a compliance deadline for your category, mark it.

Fourth, mind the NOTAMs during the transition. If you’re operating older equipment, pay attention to 5G notices near your destination. As tolerant altimeters become the standard, those restrictions should fade - but until your airplane is confirmed compliant, treat any automation that depends on the altimeter with extra awareness on a low approach.

The Bigger Lesson: Two Agencies, One Slice of Spectrum

This saga is worth studying as a case in how two federal agencies with very different missions handle a shared piece of the physical world. The FCC’s job is to extract the most public value from the spectrum. The FAA’s job is to keep airplanes from hitting the ground when nobody can see it.

Those goals collided over roughly 200 MHz of guard band, and it took years, billions of dollars, and a great deal of engineering to sort out. The system ultimately worked - nobody got hurt, and the altimeters are getting fixed - but it was closer and messier than it needed to be. The takeaway is that spectrum adjacent to aviation’s spectrum deserves a very long conversation before the auction gavel comes down.

Here is the fact you can take to the bank: after July 24, 2026, the standard for a radio altimeter in the affected fleet is no longer “works most of the time.” It has to work with a 5G tower lit up right off the approach end - and that is a genuinely safer place to be than where this started.

Key Takeaways

• The FAA’s final rule (July 24, 2026) permanently requires affected aircraft to use 5G-tolerant radio altimeters as full-power C-band service begins.
• The conflict stems from the 2021 FCC C-band auction (3.7–3.98 GHz) sitting near the radio altimeter band (4.2–4.4 GHz), separated by only about 200 MHz.
• Radio altimeters feed autoland, TAWS, auto-throttle, and low-visibility (Cat II/III) approaches - interference could cause dangerously wrong height readings.
• Transport category operators have largely complied already through 2023 airworthiness directives and an early-2024 retrofit deadline; light aircraft with radio altimeters may still be affected.
• Pilots should identify their altimeter, confirm compliance with their avionics shop, read the rule’s applicability section, and watch 5G NOTAMs during the transition.