The FAA plans to publish an Airworthiness Directive (AD) on January 27 that will limit operations of current Boeing 777 and 747-8 variants into airports where notams identify the presence of 5G C-band interference.
The FAA determined that anomalies due to 5G C-band interference might affect multiple airplane systems using radio altimeter data, including the pitch control laws that provide tail strike protection, regardless of the approach type or weather. The interference could cause missing or erroneous radio altimeter data used by the flight control system to result in what the FAA terms uncommanded, inappropriate pitch inputs, adversely affecting controllability. It could also cause multiple erroneous flight deck effects, such as misleading flight director information, erroneous autothrottle behavior, and flight mode annunciations.
When combined with the effects of the uncommanded, inappropriate pitch inputs, the flight deck anomalies could affect the flight crew’s ability to safely land, said the AD. Other systems that the missing or erroneous data could affect include the autopilot; flight director system; autothrottle system; engines; flight controls; flight instruments; traffic alert and collision avoidance system (TCAS); ground proximity warning system (GPWS); and configuration warnings.
The directive affects 336 airplanes in the U.S. and 1,714 worldwide. It does not apply to landings at airports where the FAA determined that the aircraft altimeters are safe and reliable in the 5G C-band environment. It also does not apply to airports where U.S. telecom companies Verizon and AT&T haven’t deployed 5G.
In a statement, United Airlines said that means it doesn’t anticipate any effect on its 777 operators thanks to the AD’s alternative means of compliance (AMOC), for which operators must send a request to their principal inspectors or responsible Flight Standards Office (FSO).
By Wednesday the FAA had approved at least 20 radar altimeter models for use at airports near cell towers where AT&T and Verizon plan to activate the 5G C-band, allowing for 90 percent of the U.S. commercial fleet to perform low-visibility landings at those airports. The FAA’s list of aircraft models that use cleared altimeters includes the Boeing 717, 737, 747, 757, 767, and MD-10/-11 models and Airbus A300, A310, A319, A320, A330, A340, A350, and A380 models.