A business professional is flying to a conference with a colleague as a seatmate, and it’s the final moments before takeoff. The seatmate is frantically texting a last-minute thought on their cell phone, despite the flight attendant’s warnings to put the phone in airplane mode and shut it down. Cue the spike of fear. Is the fellow employee just breaking the rules, or are they going to mess with the plane signals and crash the jet?
Though individual devices like smartphones are much less powerful than commercial transmitters, the cumulative effect of many devices, potentially interfering with aircraft systems, has traditionally been a concern. Aviation has a long history of strict protocols, advocating for passengers to switch their devices to airplane mode to prevent any potential interference with the aircraft's sensitive systems. While debates have persisted regarding the extent to which personal electronic devices could disrupt aircraft operations, aviation policies have overwhelmingly favored caution.
However, a new era of guidelines has emerged. On Jan. 9, 2023, the Federal Aviation Administration (FAA) introduced an airworthiness directive (AD), mandating that aircraft in the U.S. must be equipped to safely operate in the presence of 5G C-Band wireless signals. For passengers, this signifies a critical shift toward ensuring that airplanes can operate seamlessly alongside cutting-edge telecommunications technology such as 5G, without compromising essential systems like radio altimeters.
Dawn of 5G and aviation safety
Following a protracted period of debate over potential risks, Verizon Communications and AT&T launched 5G services on January 19, 2022. However, their approach was cautious, refraining from antenna activation near certain airport runways. The decision was made by factors such as traffic volume, the frequency of low-visibility days, and geographic location. This new era of commercial wireless communications, marked by the proliferation of 5G antennas, brought with it a wave of concerns about potential interference with radio altimeters, particularly during airport landings or adverse weather conditions.
Recognizing the gravity of these risks, the Federal Aviation Administration collaborated with the aerospace industry and wireless communications companies. Together, they navigated the landscape of rules and regulations, crafting a strategy for continued operations in the presence of C-Band 5G. To provide a structured framework, they set two critical deadlines for radar altimeter upgrades.
The first of these deadlines, set for June 30, 2023, placed restrictions on Part 121 aircraft equipped with radar altimeters that failed to meet the prescribed standards. These restrictions encompassed specific aspects of instrument landing system approaches, autolands and certain operations involving heads-up displays and enhanced flight vision systems. The second deadline, which recently took effect on Jan. 31, 2024, mandated the grounding of aircraft possessing radar altimeters that did not meet the stringent Group 4 performance criteria.
At the core of these initiatives lies a fundamental recognition of the indispensable role played by radar altimeters in ensuring aviation safety. These unassuming devices silently execute critical functions throughout various phases of flight, serving as a safeguard against collisions with terrain and obstacles. Employing diverse methodologies, including barometric, sonic, laser, GPS and radio waves, radar altimeters continuously measure and convey an aircraft's altitude relative to a reference point, typically mean sea level. This real-time data regarding the aircraft's vertical position is instrumental in maintaining safe flight operations.
Risks and concerns
The primary concern arises from the potential for harmful interference stemming from 5G C-band telecommunications systems, which operate within the frequency range of 3.4 to 4.2 gigahertz (GHz). Such interference has the capacity to impact an array of onboard aircraft equipment, including enhanced ground proximity warning systems, traffic alert and collision avoidance systems, take-off guidance systems, flight control surfaces and numerous other critical components.
In-depth examinations conducted by the International Civil Aviation Organization examine and define the far-reaching consequences of equipment failures, particularly in the context of 5G interference with radar altimeter operations.
These repercussions include:
- Nuisance warnings during take-off and approach phases
- Inhibited terrain alerting warning systems
- Interference capable of triggering abnormal behaviors within automatic flight systems
- Unreliable instrument indications
- Interference-induced erroneous commands
There are many tangible examples of the real-world challenges posed by 5G interference in aviation. NASA's Aviation Safety Reporting System database contains a repository of data regarding critical incidents that shed light on the risks associated with 5G interference in aviation. To illustrate these risks, consider the following real-world incidents.
5G interference with radar altimeter operations may lead to improved connectivity developments for the entire aviation travel industry. Source: steheap/Adobe Stock
Case study 1: Autopilot anomalies and HUD interference
A pilot flying into Sarasota/Bradenton International Airport in Florida experienced a perplexing issue during a visual meteorological conditions (VMC) approach. While the ILS Runway 14 approach was loaded as a backup in the avionics system, unexpected interference occurred. The pilot described how, at approximately 200 feet above ground level (AGL), the head-up display (HUD) began exhibiting shimmering indications, followed by the display being flooded with various data and warnings.
This interference obstructed the pilot's view through the HUD, making it impossible to use and challenging to maintain visual contact with the runway. Furthermore, ground proximity warning system (GPWS) flare callouts commenced, adding to the confusion as the aircraft wanted to initiate a flare maneuver despite being at an altitude too high for such an action.
Case study 2: Autothrottle and autopilot disruptions
A flight crew departed from Portland International Airport in Oregon. During the climb phase, the avionics system unexpectedly generated a radar altitude callout of 1,000 feet when the aircraft was at 2,300 feet. Subsequently, at 11,600 feet, the callout indicated "10," and the autothrottles disconnected.
This disruption was reported to air traffic controllers, and while the situation could have been manageable, the flight crew found themselves distracted by these unanticipated callouts. This distraction led to missed actions in resetting the altimeters and addressing other critical checklist items, potentially compromising flight safety.
These examples underscore the imperative for continuous monitoring, reporting and mitigation efforts to safeguard the integrity of flight operations and aviation safety.
Retrofitting progress
The strategy devised for seamless operational continuity in the presence of C-Band 5G revolved around a two-pronged approach involving both airlines and mobile wireless companies. Airlines were tasked with retrofitting their aircraft RAs with specialized filters designed to raise the interference tolerance level, denoted as "Group 4" performance. In return, mobile wireless companies would voluntarily limit their 5G deployments and operations to minimize the possibility of interference through Jan. 1, 2028. This cooperative mandate serves a crucial purpose: it restricts the transmission of 5G energy above the horizon and curtails power levels in the vicinity of critical airports.
However, it's important to note that this approach is not a final, permanent solution. The long-term resolution to the challenges posed by 5G interference remains under development. A potential avenue involves the exploration of new radar altimeter designs that can meet evolving standards and effectively mitigate the impact of 5G signals.
In tandem with this overarching strategy, various aircraft manufacturers and the FAA have taken proactive steps to address the issue. Their collective efforts include the issuance of guidance and ADs pertaining to specific aircraft models. These directives provide detailed instructions and regulations for the continued safe operation of aircraft in the presence of 5G interference.
Notable highlights of these manufacturer-specific guidelines and FAA ADs include:
Airbus has issued Flight Operations Transmission guidelines outlining the effects of radar altimeter anomalies for aircraft models such as the A320, A330 and A340.
Boeing and Douglas have received specific ADs from the FAA, which reference a list of C-Band Mitigated Airports where certain restrictions do not apply if the aircraft meets Group 4 performance standards. For instance:
- Boeing 747-8 and 777 (all) face operational prohibitions within the contiguous U.S.
- Boeing 787 (all) must contend with limitations related to runway conditions, increased landing distances and reduced relief from minimum equipment list requirements for braking systems.
- Boeing 737-100 to -900ER confront restrictions on autopilot use during go-around/missed approach, manual speed brake deployment and mandatory go-around in cases of anomalous behavior during ILS approaches.
- Boeing 757/767 (all) experience increased landing distances, the elimination of autopilot/flight director use during ILS approaches, modified go-around procedures and mandatory manual speedbrake deployment when necessary.
- Boeing 747-100 to -400 encounter the elimination of autopilot/flight director use during ILS approaches, alongside modified takeoff, landing and go-around/missed approach procedures.
- DC9/MD80/MD90/B-717, DC10/MD11, B-707 and B-727 aircraft undergo modifications to autopilot use for ILS, approach, landing and missed approach procedures, as well as increased landing distances.
- Embraer has issued Flight Operations Letters and Operational Bulletins elucidating the potential effects of C-Band 5G interference on its E170, E175, E190 and E195 aircraft models.
In assessing the scale of these initiatives, the FAA estimated that approximately 180 airplanes on the U.S. registry would necessitate radio altimeter replacement, while an additional 820 airplanes would require the installation of radio altimeter filters to comply with the proposed modification requirements. The overall estimated cost of these compliance measures was projected at $26 million.
As of June 2023, the U.S. Department of Transportation reported significant progress in this endeavor. Over 80% of aircraft in the U.S. had already undergone upgrades to their radio altimeters. However, a disparity existed, with only approximately 65% of international aircraft flying into the U.S. having undergone retrofitting. It's worth noting that the U.S. Department of Transportation cautioned travelers about the potential for flight delays due to non-compliance with updated altimeter requirements among some aircraft. Nevertheless, there has been no substantiated evidence of such delays occurring.
Future of air travel with 5G
The ultimate benefit of 5G for air travel will come via full connectivity for the airplane itself.
5G can unlock a host of benefits and make the travel experience safer and more pleasant. While in transit, passengers are likely to receive better quality streaming services while communication between pilots and air traffic control will become seamless. Enhanced technology in the cockpit could also support autonomous flight operations and translate into optimized flight operations. More data, easily processed and analyzed, might result in better maintenance, and expedited turnaround, paving the way for tighter and more predictable scheduling.
Conclusion
The integration of 5G technology into aviation has presented a unique set of challenges and opportunities. While concerns over potential interference with aircraft systems have historically led to stringent protocols regarding personal electronic devices on flights, the shift in aviation policies, requiring aircraft in the U.S. to be equipped to safely operate around 5G C-Band wireless signals, ensures the coexistence of this technology with essential aircraft systems.
Moving forward, the journey toward fully integrating 5G technology into aviation will likely involve continuous collaboration among technology providers, aircraft manufacturers and regulatory bodies. This collaborative effort is crucial for developing more robust systems that can coexist with 5G signals without compromising safety.
About the author
Emily Main holds a J.D. in Compliance Law and a BS in Telecommunications. With extensive experience in the intersection of technology and law, Main has contributed to numerous publications and conferences, exploring technical challenges, innovations, trends and applications. Passionate about communication and networking, she is dedicated to sharing the latest advances in the field with a professional engineering audience through engaging and informative articles.
