By Chris Rusing, Attorney, Aviation Law Group

The answer is YES!

5G wireless technology is the planned successor to 4G broadband telecommunication cellular networks that provides cellphone network services to most current cell phones. Like 4G networks, 5G networks are divided into cells where wireless devices are connected to the telephone network and internet through radio waves communicating with an antenna within the cell. Due to the increased bandwidth over 4G technology, 5G (allowing for higher download speeds and increased connectivity of more devices) is the future of broadband telecommunications with an estimated 1.7 billion subscribers worldwide by 2025.

Last year, the Federal Communications Commission (FCC) awarded the mobile wireless radio spectrum to operate 5G communications to Verizon and AT&T. The 5G technology operates in 3.7-3.98 GHZ also known as the “C-Band.” The FCC made the award despite the aviation industry warning the FCC since 2018 of the potential interference transmissions within the C-Band could have with radio altimeters which play an integral part in modern transport category aircraft safety.

Radio altimeters, also known as radar altimeters, use radio waves to measure the height of an aircraft from the ground/water by sending radio signals downward and calculate the amount of time it takes for the radio waves to reflect from surface of the earth to the aircraft. The altitude above the surface is calculated by the radio waves’ travel time and the speed of the radio waves, that being the speed of light. Following World War II, radio altimeters became a standard instrument on commercial aircraft enhancing safety, especially in low visibility and uneven terrain.

Commercial aviation radio altimeters operate in the 4.2-4.4 GHz band, which is separated by 220 megahertz from the C-Band telecommunication systems in the 3.7-3.98 GHz band. The radio altimeter is more precise than a barometric altimeter and for that reason is used where aircraft height over the ground needs to be precisely measured. The receiver on the radio altimeter is typically highly accurate, however it may deliver erroneous results in the presence of out-of-band radiofrequency emissions from other frequency bands. Out-of-band signals could significantly degrade radio altimeter functions during critical phases of flight or even provide incorrect indications of altitude, if the altimeter is unable to sufficiently reject those signals.

In the past several decades transport category aircraft manufacturers automated many functions and introduced complex computers to not only decrease pilot workload, but to increase passenger safety. Modern transport category aircraft manufacturers like Boeing and Airbus increasingly incorporated the use of the radio altimeters into multiple flight control systems and warning systems. Aircraft systems that could potentially be affected by erroneous radio altimeter indications on both Boeing and Airbus aircraft include the primary flight displays, systems displays, warnings and auto callouts, flight control laws, [1] ground proximity warnings, high and low speed protections, auto thrust and auto throttle, excessive angle of attack protections, and low visibility landing capability. Due to how important radio altimeter indications are to so many aircraft systems, accurate radio altimeter data is vital to the safe conduct of the flight.

two pilots sitting inside plane
Photo by Rafael Cosquiere on

Faulty radio altimeter data is a serious safety of flight issue. Incorrect radio altimeter data resulted in nine fatalities in a Turkish Airlines Boeing 737-800 crash in Amsterdam in 2009. Aviation Law Group represented numerous families who lost loved ones in that accident, commonly referred to as TK 1951.

On final approach to Amsterdam’s Schiphol Airport the captain’s radio altimeter failed, erroneously indicating the aircraft much lower than it was flying. The first officer failed to correctly arm the autopilot for the approach, and the aircraft’s autopilot relied on the captain’s radio altimeter indication. As result of the lower altitude indication, the computer logic calculated that the aircraft was attempting land; the autothrottles reverted to idle and the aircraft slowed to a speed where it could not maintain flight crashing short of the intended runway. As the Turkish Airlines crash demonstrated, erroneous data from radio altimeters can have catastrophic consequence to the safe conduct of flight.

The extent of 5G interference with radio altimeters is continuing to be investigated by many organizations including the Federal Aviation Administration (FAA) and aircraft manufacturers such as Boeing and Airbus. Initial findings that C-Band transmissions should not interfere normal aircraft operations. However, subsequently testing found that C-Band transmission do indeed cause adverse effects on radio altimeter systems when the transmission power was increased.

As a result of the potential adverse effects of 5G on radio altimeters, the FAA issued Airworthiness Directive (AD) 2021-23-12. The AD stated that “[t]he FAA is issuing this AD because the agency has determined the unsafe condition [of 5G radio altimeter interference] is likely to exist or develop in transport and commuter category airplanes with a radio altimeter as part of their type design.” The AD went further to require airlines “to incorporate limitations prohibiting certain operations requiring radio altimeter data when in the presence of 5G C-Band wireless broadband signals. These limitations could prevent dispatch of flights to certain locations with low visibility, and could also result in flight diversions.”[2] As a result of the AD, hundreds of flights were cancelled due to the potential unavailability of certain aircraft systems that would allow for landing in low visibility conditions.

Most recently the FAA has updated its policy regarding certain aircraft after further testing. The FAA recently found that altimeters for most of the in-service US airline operated Airbus, Boeing and Embraer aircraft were cleared from vulnerability to any interference issues. However, on January 25, 2021, the FAA issued an AD prohibiting Boeing 747-8, 747-8F and 777 airplanes from landing at airports where 5G interference could occur. The AD does not apply to landings at airports where the FAA determined the aircraft altimeters are safe and reliable in the 5G C-band environment. It also does not apply to airports where 5G isn’t deployed. This AD affects approximately 336 airplanes in the United States and 1,714 worldwide.   

The potential effects of radio altimeter interference is an ongoing an evolving aviation safety issue.

Robert Hedrick, J.D., LLM

What if there is an aircraft accident caused by 5G interference with a radio altimeter?

If the accident occurs in the U.S., and the passenger tickets are domestic (within the U.S.), then the liability law of the U.S., federal and/or state will come into play.  Liability depends upon the facts of each case. Foreseeable at-fault parties would include the airline/operator, the 5G provider(s), the FAA, and possibly aircraft and component part manufacturers associated with the radio altimeter.  Any court litigation would likely involve a lot of expert analysis and opinions, and ultimately finger pointing between the defendants. If the case went to trial, a jury would allocate fault between the defendants on a percentage basis totaling 100%, which would determine the allocation of payments to the plaintiffs.

[1] Computer automation known as flight control laws use automated systems and the information supplied by instruments such as the radio altimeter to monitor, warn, and potentially step to provide corrective action if the safety of flight becomes an issue.

[2] AD 2021-23-12