The fifth generation (5G) cellular network offering increased high-speed data uses a range of frequencies. These frequencies (also known as C-band) have the potential to interfere with radio altimeters used on aircraft. Radio altimeters, which also use C-band frequencies, have been successfully used on aircraft for decades. In addition to providing the aircraft altitude, the radio altimeter connects to several critical aircraft systems.

The altitude information transmitted through the radio altimeter is critical to automatic landing systems, flight controls, primary displays, crew alerting, and surveillance, just to name a few. Radio altimeters differ from standard altimeters, which only provide the aircraft's altitude above sea level by measuring atmospheric pressure.

The authorized power limits for 5G networks can pose significant safety risks to aircraft, especially around airports at low altitudes. Aviation regulators, airlines, and aircraft manufacturers are working together to address the issue. Boeing's Chief Engineer and Executive Vice President of Engineering, Test, and Technology, Howard McKenzie, commented during Boeing's Quarterly Innovation Release,

"Advancements in wireless technologies are continuing. While industry, regulators, and airlines are rigorously partnering to address the introduction of 5G towers in proximity with airport operations now, we're also focused on applying what we learn here to get ready for future developments."

Regulatory measures

The Federal Aviation Administration (FAA) has taken measures to keep aviation safety intact by imposing operational restrictions for various aircraft and airports. The FAA has proposed guidelines for different aircraft types to be equipped with radio altimeters approved for 5G environments.

Boeing is conducting extensive research and data collection through flight testing to analyze the occurrences where 5G networks can interfere with aircraft radio altimeters. Boeing's technical team is also checking each airplane's altimeter installation against the alternative method of compliance (AMOG) methodology set by the industry.

The AMOC method allows the FAA to identify the compatibility of aircraft altimeters with active 5G base stations. Based on the information, certain restrictions (or removal of restrictions) can be set to assure the continued safety of the aircraft. According to Matt Hams, a Boeing Technical Fellow specializing in radio navigation systems,

"Aviation is making progress on developing new standards with our partners at the FAA, the FCC (Federal Communications Commission), and in the telecommunications industry. We know this is an important issue, and Boeing teams will continue to work toward the safe and efficient solutions needed now and into the future."

Boeing's research and flight tests

Boeing aims to find technical, regulatory, and operational solutions to 5G's interference issue with the radio altimeter. While collaborating with its partners, Boeing's technical team ensures that the appropriate data is gathered to analyze the effect of 5G frequencies on critical aircraft systems. For example, the automatic flight system uses the altitude transmitted via the radio altimeter to conduct auto-pilot approaches in low visibility conditions.

Any interference in the timing of the flare, auto-throttle, and thrust reversers is critical to the safe operation of the aircraft. The FAA states that any interference of 5G networks with existing equipment could delay systems like thrust reversers. A radio interference could prevent the Boeing 787s thrust reverser from initiating upon landing, leaving only the brakes to slow the jet. This may result in preventing the aircraft from stopping on the runway.

A Boeing 787 in house livery flying above the clouds.
Photo: Boeing

Moreover, the Boeing 787s may not properly transition from flying mode to landing mode due to the 5G interference. This could delay the activation of systems critical for slowing the plane for approach and landing. Action is taken to restrict specific landings and the use of certain minimum equipment list (MEL) items. Longer landing distance procedures, as directed in the AD from February 2022, must apply to all runway conditions and be incorporated into existing flight manuals before June 30, 2023.

While many US-based airlines request the FAA to extend the deadline to June 2024, Boeing continues to gather flight data in various 5G environments. Boeing engineers across the globe collect such operational data to understand the extent to which the interference occurs and to provide ways to overcome those.

Similarly, the Ground Proximity Warning System (GPWS) and the Traffic Collision Avoidance System (TCAS) rely heavily on the radio altimeter. While the GPWS calculates aircraft's proximity to the ground or terrain, the TCAS prevents collisions with other aircraft by calculating the closure rate between aircraft. For either system, preventive alerts and maneuvers are made to avoid catastrophic events.

An erroneous altimeter reading can seriously jeopardize the safety of aircraft and its occupants. With the understanding of how radio altimeters are integrated into various systems on airplanes, technical teams at Boeing are keen to find ways in which the new 5G cellular technology can safely coexist with the operation of aircraft of all types.

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Flight tests

Boeing's flight engineering team configures various airplanes for test conditions; an extensive set of tests are conducted, and real-time data is gathered. Data from multiple critical systems, including the automatic flight system, is collected for analysis.

Boeing provides guidelines for some airplanes to adopt extra procedures during approach and landing, especially on wet or snowy runways. While the officials understand the extent of the interference issue, it is safer to add a safety net to the existing procedures.

A Boeing 787 in house livery flying over land.
Photo: Boeing

The information revealed from the flight tests is used to develop and manufacture equipment that limits the 5G interference on Boeing planes. The senior manager of Avionics Engineering at Boeing, Matt Sunday, comments.

"Once industry and regulators identified a path forward for near-term equipment needs in the fleet, the broader Boeing team jumped right in. We've worked with Supply Chain, Engineering, Customer Support, Boeing Research & Technology, and others to face the challenge head-on. We've helped lead the industry to ensure the continued safety of our products."

Sunday's team certifies and deploys essential hardware onto Boeing airplanes to eliminate the 5G interference. Apart from individual system tests, ground and flight tests are conducted to ensure new hardware is compatible with the system and also prevents cellular interference.

What are your thoughts on the importance of flight data acquired to ensure flight safety in 5G environments? Tell us in the comments section.

  • 787-8 Dreamliner
    Boeing
    Stock Code:
    BA
    Date Founded:
    1916-07-15
    CEO:
    Dave Calhoun
    Headquarters Location:
    Chicago, USA
    Key Product Lines:
    Boeing 737, Boeing 747, Boeing 757, Boeing 767, Boeing 777, Boeing 787
    Business Type:
    Planemaker