New Airworthiness Directive Addresses B747, 777 5G Interference

The FAA has released another 5G related Airworthiness Directive, this time prohibiting Boeing 747-8, 747-8F and 777 airplanes from landing at airports where 5G interference could possibly occur.

The AD does not apply to those landings at airports the FAA has affirmed are safe and reliable in their local C-band environment, nor those airports without 5G infrastructure in their vicinity. The FAA says it issued the AD for the heavy Boeings because of its interconnected systems reliant upon its altimeter, which affects the autothrottle, ground proximity warning, thrust reversers, and TCAS. The aircraft affected are estimated to number 336 in the domestic American fleet, with over 1,700 worldwide. The agency has given a short window to assume compliance, those affected must work within its requirements by January 27th. 

The AD says that "AD 2021-23-12 requires revising the limitations section of the existing AFM to incorporate limitations prohibiting certain operations, which require radio altimeter data to land in low visibility conditions, when in the presence of 5G C-Band interference as identified by NOTAM." On the model-specific concerns, the agency mentions the "additional hazard presented by 5G C-band interference on The Boeing Company Model 747-8F and 747-8 series airplanes and Model 777 airplanes. The FAA determined that anomalies due to 5G C-Band interference may affect multiple airplane systems using radio altimeter data, including the pitch control laws, including control laws that provide tail strike protection, regardless of the approach type or weather. These anomalies may not be evident until very low altitudes. 

"Due to 5G C-Band interference, missing or erroneous radio altimeter data used by the flight control system may result in uncommanded, inappropriate pitch inputs, adversely affecting controllability. This interference could also cause multiple erroneous flight deck effects, including misleading flight director information and erroneous autothrottle behavior and Flight Mode Annunciations. These flight deck effects, when combined with the effects of the uncommanded, inappropriate pitch inputs, could affect the flight crew’s ability to accomplish continued safe flight and landing. Other systems that could be impacted by this missing or erroneous data, and contribute to this hazard, include, but are not limited to: 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."

FMI: www.faa.gov. www.boeing.com