The FAA issued an Airworthiness Directive (AD) preventing Boeing 747-8, 747-8F, and 777 planes from landing at airports where 5G interference may occur.
The FAA stated in the document that airlines flying Boeing 747-8s, 747-8Fs, and 777s must revise the existing limitations section of the airplane flight manual (AFM) “to incorporate limitations prohibiting dispatching or releasing to airports, and approaches or landings on runways” where 5G C-Band may cause interference.
C-Range telecommunication services operate in the 3.7-3.98 GHz spectrum in the United States, while commercial aviation radio altimeters use the 4.2-4.4 GHz band.
Radio altimeters fitted on 747-8, 747-8F, and 777 airplanes, according to the FAA, could display deceptive data if interfered with.
Various plane systems receive immediate height-above-terrain and water information from the aircraft radio altimeter.
This electronic instrument is used to properly estimate aircraft height over the ground during manual landings, autoland, or other low-altitude operations. It is more exact than a barometric altimeter.
While the radio altimeter’s receiver is normally very accurate, it may produce inaccurate data “in the presence of out-of-band radio frequency emissions from other frequency bands,” according to the FAA.
This means that the altimeter is unable to reject out-of-band signals effectively, which could cause the instrument to malfunction during crucial flight phases such as take-off, final approach, and landing.
Many systems on Boeing 747-8, 747-8F, and 777 aircraft, including autothrottle, ground proximity warning, thrust reversers, and Traffic Collision Avoidance System, rely on the altimeter, according to the authority.
The FAA stated that it “is issuing this AD to address the unsafe condition on these products.”
The AD does not apply to landings at airports where the FAA has concluded that aircraft altimeters in the 5G C-band environment are safe and reliable. It also doesn’t apply to airports that haven’t implemented 5G.
The AD is expected to affect 336 planes in the United States and 1,714 planes worldwide.