ADVANCING AVIATION SAFETY AND SECURITY SINCE 1931

Aircraft Operations and Radar Altimeter Interference from 5G

June 29, 2023

ALPA will update this page with additional operational resources and information for pilots as they become available. Learn more about this issue.

Background/Current Status

United States

In early 2021, the Federal Communications Commission (FCC) awarded the mobile wireless industry radio spectrum to operate 5G transmissions in the “C-Band,” or 3.7-3.98 GHz, adjacent to the spectrum used by radar altimeters. This approval was made despite the aviation industry informing the FCC since 2018 of the need to ensure that radar altimeters are protected from 5G interference. The 5G signals in the United States are at higher power levels than any other deployment currently in use elsewhere in the world and also with closer proximity to airports. 

In the United States, wireless broadband deployment was originally scheduled to begin on December 5, 2021. After high-level talks, mobile wireless has agreed with the Federal Aviation Administration (FAA) to delay broadcast of C-Band 5G until January 19, 2022, and placed voluntary limitations to C-Band 5G deployment until July 5, 2022, to permit continued access to airport by a substantial portion of the airline fleet. Since that time, FAA, radar altimeter manufacturers, and mobile wireless companies have continued to exchange information and have modified and extended the agreements several times.

In January 2023, the FAA announced its strategy for continued operations in the presence of C-Band 5G for the mid-term. Airlines would retrofit aircraft or radar altimeters with filters to achieve a high interference tolerance level (called “Group 4” performance), and in return, mobile wireless companies would continue to voluntarily limit their deployments and operations to minimize the possibility of interference through January 1, 2028. This voluntary limit would limit the amount of 5G energy transmitted above the horizon and would also limit power in the vicinity of critical airports (e.g., those with CAT II/III ILS approaches). The FAA has issued a final rule that implements this strategy by revising the original “blanket” AD 2021-23-12 that was originally issued in late 2021.

The long-term solution is yet to be determined but may involve new radar altimeter designs that meet new standards currently under development.

The AD imposes two deadlines for upgrading radar altimeters. The first is June 30, 2023, after which Part 121 aircraft with radar altimeters that do not meet the required performance will be restricted from flying ILS CAT II/III approaches, autolands, and some heads-up display (HUD)/enhanced flight vision system (EFVS) operations. In addition, several aircraft have model-specific ADs that modify aircraft procedures in the presence of 5G (see below); these will also apply to aircraft not meeting the required performance.

The second deadline is January 31, 2024, after which aircraft with radar altimeters that do not meet the required Group 4 performance will be grounded for Part 121 operations. In discussions with the airline industry, it appears that while most of the about 7,000 Part 121 aircraft in the United States will meet the required Group 4 performance standard on June 30, 2023, a few hundred aircraft might not be ready and will be restricted from flying CAT II/III ILS, autoland, and some HUD/EFVS operations. Airlines have indicated that they will manage these aircraft operationally (e.g., via routings that avoid low-visibility airports.)

Canada

Canada has also approved 5G in the C-Band, but with restrictions against using C-Band in the vicinity of 26 airports and other measures to ensure aviation safety. Innovation, Science and Economic Development Canada and Transport Canada have worked together to perform laboratory and flight testing of radar altimeter equipment in the presence of C-Band 5G transmissions and have confirmed that interference is a possibility from C-band 5G in Canada and the United States. 

Canada has convened a 5G Radar Altimeter Working Group within the Radio Advisory Board of Canada to work through what operational limitations would apply on both mobile wireless and aviation to ensure safety as Canada plans 5G deployment. These discussions, in which ALPA participates, are still in process.

Keep reading for guidance on both U.S. and Canadian airline operations.

Flight Safety Concerns

Radar altimeter interference from 5G signals can take the form of loss of radar altitude information or, worse, incorrect radar altitude information unknowingly being generated. There have been fatal accidents associated with incorrect radar altitude, most recently Turkish Airlines Flight 1951 in Amsterdam in 2009.

Altitude information derived from radar altimeters has been deeply integrated into aircraft systems and automation, with the latest aircraft using it to change aircraft handling qualities and prepare systems such as ground spoilers and thrust reversers for deployment prior to touchdown. This is in addition to radio altimeter use for autoland and in Category (CAT) II/III ILS. 

FAA Actions and Operational Updates

• On November 2, 2021, the FAA issued a special airworthiness information bulletin (SAIB) alerting operators to the potential for severe restrictions in flight operations to ensure safety. Updates were published on December 23, 2021; October 18, 2022; and May 24, 2023. The current version is SAIB AIR-21-18R3.
• On May 25, 2023, the FAA issued a revised Airworthiness Directive (AD) covering all transport category airplanes. The AD requires the following Airplane Flight Manual (AFM) revision, which prohibits the following operations by airplanes that do not meet the required (Group 4) performance. Note that this restriction applies until January 31, 2024, after which the aircraft will be grounded for Part 121 operations:

Figure 4 to paragraph (i) — AFM Revision for Non-Radio Altimeter Tolerant Airplanes (Required by AD 2021-10-02)

Radio Altimeter Flight Restrictions

Through June 30, 2023, when flying in U.S. airspace, the following operations requiring radio altimeters are prohibited in the presence of 5G C-Band wireless broadband interference as identified by NOTAM (NOTAMs will be issued to state the specific airports where the radio altimeter is unreliable due to the presence of 5G C-Band wireless broadband interference): 

• Instrument Landing System (ILS) Instrument Approach Procedures (IAP) SA CAT I, SA CAT II, CAT II, and CAT III 
• Automatic landing operations 
• Manual Flight Control Guidance System operations to landing/HUD to touchdown operation 
• Use of EFVS to touchdown under 14 CFR 91.176(a)

Simplified NOTAMs have been reissued in the contiguous United States (CONUS) for the 20 US Air Route Traffic Control Centers and airports with affected ILS approaches (Excel file). These NOTAMs restate the AD restrictions for the specific approaches.

Guidance and Limitations by Aircraft Manufacturers

In addition to the blanket AD, aircraft manufacturers have published guidance, and FAA has issued additional ADs against specific aircraft models. These restrictions will continue to be required for aircraft not meeting Group 4 performance after June 30, 2023, and will apply everywhere in the CONUS after that date.

• Airbus has issued Flight Operations Transmission 999.0002/22 (01/10/2022) which describes the currently understood effects of radar altimeter anomalies. Guidance is provided for A320 family, A330, and A340 aircraft for handing these anomalies. No effects are currently expected for A300/A310, A350, and A380 aircraft.
• The FAA has issued airworthiness directives against specific Boeing and Douglas models.  These have been updated to apply everywhere in the CONUS. These ADs reference an FAA Domestic Notice with a list of C-Band Mitigated Airports, where the restrictions do not apply if the aircraft meets Group 4 performance. 

• Boeing 747-8 and 777 (all): AD 2023-12-05 prohibits all operations in the CONUS.
• Boeing 787 (all): AD 2023-12-10 limits runway conditions, increases landing distances, and reduces MEL relief for braking systems.
• Boeing 737 MAX (all): AD 2023-12-11 limits runway conditions, increases landing distances, and reduces MEL relief for braking systems.
• Boeing 737-100 to -900ER (except modified B-737-200/200C): AD 2023-12-13 limits autopilot use during go-around/missed approach, manual deployment of speedbrakes if needed, and requires go-around if anomalous behavior is encountered on ILS approaches.
• Boeing 757/767 (all): AD 2023-12-12 increases landing distances, eliminates autopilot/flight director use during ILS approaches, modifies go-around procedures, and requires manual deployment of speedbrakes if needed.
• Boeing 747-100 to -400: AD 2023-12-14 eliminates autopilot/flight director use during ILS approaches; modifies takeoff, landing, and go-around/missed approach procedures.
• All DC9/MD80/MD90/B-717, all DC10/MD11, all B-707, all B-727: AD 2023-12-15 modifies autopilot use for ILS; modifies approach, landing, and missed approach procedures; increases landing distances for some aircraft.

• Embraer Flight Operations Letter 170-001/22 and Operational Bulletin 170-001/22 (01/02/2022): Describe the possible effects of C-Band 5G interference on its E170, E175, E190, and E195 aircraft. Note: The FAA has not yet issued ADs based on these bulletins.
• Additional restrictions or limitations will be listed here when they are published.

Alternate Methods of Compliance

From January 19, 2022, to June 30, 2023, the FAA has issued Alternate Methods of Compliance (AMOCs), which lists airports and runways where particular combinations of aircraft and radar altimeters could safety disregard the 5G NOTAMs and ADs. However, these AMOC lists will be rendered obsolete after June 30, 2023. After this date, all aircraft will be subject to AD limitations unless they meet Group 4 radar altimeter performance.

Additional ALPA Recommendations

It is critical for pilots to be aware of and comply with any restrictions imposed via AD, AFM, and NOTAMs by the FAA and airline. The flight manual restrictions from the airworthiness directive coupled with NOTAMs that inform of the presence of 5G (C-Band) or restrictions of specific instrument procedures are important triggers, with which pilots must carefully evaluate their aircraft’s ability to be safely operated and determine what additional contingencies must be considered.

In addition, pilots need to be aware of whether the aircraft meets “Group 4” performance for 5G tolerance, as this will determine whether ADs and modified procedures apply starting on July 1, 2023.

During flight planning and advanced preparation, consider whether the weather forecast allows for the use of the available instrument approach procedures, should an alternate airport be required. Alternate airports may need to be selected that are further away from the intended destination and may impact fuel loading plans significantly.

Follow company guidance for operating in the 5G interference areas and actively pursue information from your air carrier when you have questions. 

Pilots are also advised to:

• Always err on the side of caution.
• Reinforce to passengers that all phones must be in airplane mode.
• Know the equipage of the specific aircraft you will be flying, and any limitations.
• Remember that air traffic control (ATC) doesn’t know the capabilities or limitations of the aircraft you are operating.
• Inform ATC of your limitations as needed and be prepared to utilize “unable.”
• Read the AD and NOTAMs very carefully for your airports and alternates.
• The AD and NOTAMs will discuss very specific combinations of approaches and aircraft functions that are not authorized.
• In addition, the NOTAMs may change rapidly on a daily or weekly basis as further data is analyzed. It is imperative a thorough review of the NOTAMs is conducted before each flight.
• Before July 1, 2023, have documentation of any AMOC that allows the AD/NOTAM to be disregarded.
• On and after July 1, 2023, have documentation of whether your aircraft meets the radar altimeter performance standard (“Group 4” tolerance level).
• Utilize dispatch to carefully screen what limits are in place for the airports and alternates, including
• Weather and forecasts and
• Fuel load and contingency plans for diversion and ATC flow control actions.
• Be especially aware of any anomalies during operations below 5,000 feet AGL.
• Follow any guidance provided by your airline and, in the case of conflicting guidance, follow the airline procedures.

Report Radar Altimeter Anomalies

If a radar altimeter anomaly is seen in operations:

• Report issues immediately to ATC.
• Report any issues or experiences via ASAP/SMS after the flight is complete.
• Also, after flight completion, submit a radar altimeter anomaly report:
• US pilots are requested to file an FAA anomaly report. 
• Canadian pilots are also requested to report any anomalies to Transport Canada. Adobe Reader is required to open the form. The form requires input from both the Pilot-In-Command and the airline operator. Fill out Parts 1 and 3 of this form, then submit to your airline using the process established by the airline. In the event that a company does not have a process set up to fill out Part 2 of this form, ALPA recommends that pilots send the partial report to Transport Canada to the e-mail address at the bottom of the form.

Canadian Operations

Canadian Aviation Regulation 605.84 already requires U.S.-type-certificated aircraft registered in Canada to comply with U.S. ADs when operating in the United States.  Transport Canada has issued the updated Canadian Airworthiness Directive CF-2023-46 extending this requirement to all Canadian-registered aircraft that fly in the United States, and Canadian members are therefore also prohibited from performing the operations listed above on this page when operating an airplane that does not meet Group 4 performance on or after July 1, 2023.

Canada has also approved 5G in the C-Band, but with interim restrictions against using C-Band in the vicinity of 26 airports, and other measures to ensure aviation safety. Longer-term restrictions on 5G and possible aviation equipment upgrades are currently being discussed by the Canadian spectrum regulator ISED and Transport Canada.

 

26 Protected Airports in Canada
Abbotsford	CYXX
Calgary	CYYC
Charlottetown	CYYG
Churchill	CYYQ
Edmonton	CYEG
Fort McMurray	CYMM
Fredericton	CYFC
Gander	CYQX
Moncton	CYQM
Halifax	CYHZ
Iqaluit	CYFB
Hamilton	CYHM
London	CYXU
Montreal Mirabel	CYMX
Montreal Trudeau	CYUL
Ottawa	CYOW
Prince George	CYXS
Quebec City	CYQB
Regina	CYQR
Saskatoon	CYXE
St John’s	CYYT
Thunder Bay	CYQT
Toronto	CYYZ
Vancouver	CYVR
Winnipeg	CYWG
Yellowknife	CYZF

 

View an interactive map showing the location and extent of protected and exclusion zones around these airports.

Discussions are still ongoing as to the approach Canada will take in the near-to-mid-term, but it is expected to be somewhat aligned with the U.S. plan. Any additional restrictions on operations by Transport Canada will be added here as they become available.