The FAA has expressed concern and issued a warning about the interference that the 5G C-band poses to the landing process at a number of airports, mostly for the Boeing 737. They also stressed that this warning does not apply to landings at airports where 5G isn’t deployed, and at airports where radio altimeters have been determined to function smoothly and “are safe and reliable in the 5G environment.”

In January, the FAA green-lit all 737 models to land at airports when using radio altimeters in low-visibility conditions even if 5G-C cellular towers are nearby.

Now it seems that the Association has changed its mind after all; radio altimeters cannot be relied upon to perform their intended function if they experience interference from wireless broadband operations in the 5G C-band. Another aggravating circumstance is the pressure that this type of interference puts on pilots and the entire aircraft and airport staff.

The FAA issued its Airworthiness Directive (AD) because several of the systems on the Boeing 737 rely on the radio altimeter to function properly. These include the autopilot flight director system, ground proximity warning system, autothrottle system, and traffic alert and collision avoidance system.
The AD affects about 2,442 aircraft in the United States and 8,342 worldwide, so it could pose a serious problem for air travel around the globe.

Although Boeing Model 737-100, -200, -200C, -300, -400, -500, -600, -700, -700C, -800, -900, and -900ER series airplanes are included in the directive, the 737-200 and -200C series are equipped with a different flight control system (SP-77) that should not be affected by 5G signals in any way.

Rather than specifying which airports have reported the issue, the FAA plans to issue NOTAMs (Notices to Air Missions) which would officially confirm that aircrafts’ radio altimeters are unreliable due to the presence of 5G C-Band wireless broadband interference. So far, the FAA identified 87 airports that require the use of altimeters for safe landing due to low visibility.