Potential Risk of Interference of 5G Signals on Radio Altimeter - Civil Aviation Safety Alert (CASA) No. 2024-05

Attention:

All Canadian Operators Equipped with a Radio Altimeter and Air Traffic Service

File Classification No.:	Z 5000-35
RDIMS No.:	20289980
Document No.:	CASA 2024-05
Issue No.:	01
Effective Date:	2024-05-06

Purpose:

The purpose of this Civil Aviation Safety Alert (CASA) is to complement Civil Aviation Safety Alert 2023-06 regarding potential risk of 5G interference.

Transport Canada (TC) has studied the equivalency of the Canadian spectrum environment to the U.S. to determine whether the 5G tolerance requirements for radio altimeters (RadAlt) set by the Federal Aviation Administration (FAA), known as “Radio Altimeter Tolerant”, can be leveraged for the Canadian environment. TC has accepted the scientific conclusions from Innovation, Science, and Economic Development (ISED) Canada and as validated by the Communications Research Centre Canada (CRC) related to the safe operation of radio altimeters in the planned Canadian spectrum environment.

Background:

ISED is the spectrum regulator in Canada. Since December 2021, ISED has allowed flexible use networks and technology (including 5G) in the frequency bands 3450 to 3650 MHz (3500 MHz). ISED will allow (5G) in the frequency band 3650-3900 MHz (3800 MHz) following its auction on October 24, 2023. Deployment in the 3800 MHz band may begin incrementally in some locations as early as May 29, 2024. Additionally, ISED recently concluded consultation on non-competitive licensing (NCL) framework to operate in the frequency band 3900-3980 MHz. The frequency bandwidth allocated to these services are close to one used by aircraft radio altimeters (4200-4400 MHz).

5G is also already deployed in the United States as well as in several countries in Europe and Asia, with power levels and spectrum mitigations varying from country to country.

Given the worldwide expansion of this technology, data gathered by the FAA, ISED, the Radio Technical Commission for Aeronautics (RTCA) and others, Transport Canada concluded there exists a possibility of disturbance for certain radio altimeter (RadAlt) models by 5G radio waves in numerous operational scenarios in the frequency band 3450-3980 MHz at or above a specific power spectral density (PSD) curve threshold, which may affect aviation safety. The FAA has issued several Airworthiness Directives (ADs) to mitigate the risk to aviation safety in the U.S. 5G environment.

Transport Canada (TC) also intends to issue ADs to apply aviation limitations including placarding requirements, to aircraft that may not be tolerant to the Canadian 5G environment where 5G may have been deployed. In order to maintain aviation safety for aircraft that are not equipped with 5G-tolerantequipment, issuance of the first of these ADs is expected by mid-May 2024 and are expected to reflect similar operating limitations and retrofit options as presented in FAA equivalent ADs CF-2023-46 and CF-2023-49. Possible alleviations to upcoming aviation limitations are explained in Appendix A of this CASA notice.

All operators are encouraged to proactively plan to retrofit their aircraft to Radio Altimeter Tolerant, where the replication of the FAA Generic Fixed Wing and Rotary Wing restrictions, and aircraft specific restrictions would impact their operations, by securing maintenance slots, parts, and supplemental type certificates (STCs), and adjust accordingly based on final retrofit requirements that will be published.

Aircraft may need to be Radio Altimeter Tolerant by December 31st 2025 in order to be alleviated from operational limitations at airports where 5G has been deployed. Non-Radio Altimeter Tolerant commercial aircraft may be limited to transporting cargo only on January 1st, 2026, and may be prohibited from transporting passengers (excluding aircraft personnel, as well as medical personnel and patients for medical evacuation operations) at airports in proximity of where 5G has been deployed. January 1st, 2026 represents a planned sunset date of current spectrum mitigations at which time, Radio Altimeter Tolerant aircraft may require re-evaluation of necessary operational limitations and/or mandatory retrofit requirements.

In July 2023, ISED established technical rules in the 3450-3900 MHz bands to mitigate potential interference to radio altimeters, which extends the technical rules for the 3450-3650 MHz band (3500 MHz) that were initially published by ISED in November 2021. The main protection measures, which under the current plans, are to be maintained until at least January 1, 2026 include:

• Exclusion and protection zones to mitigate interference to aircraft having a certain level of 5G tolerance at certain runways (see Appendix C) at 35 airports covering 93% of air traffic in Canada;
• Reduced fundamental emissions power levels at the runways at the 35 airports having protection and exclusion zones, implemented by E.I.R.P. elevation mask^{Footnote 1}; and
• Reduced fundamental emissions power levels based on degree of antenna uptilt above the horizon, nationwide, to minimize skyward emissions from 5G base stations.

Protected runways (in Appendix C) only offer protection to aircraft that can withstand a certain level of 5G fundamental and spurious emissions. Aircraft with non-5G-tolerant radio altimeters may face stringent limitation where 5G may have been deployed at non-protected airports.

Potential Way Forward Under Consideration:

Following its review of the future Canadian 5G environment, the following actions could be recommended by TC for Non-Radio Altimeter Tolerant aircraft:

1. Autoland procedures, Instrument Landing System (ILS) Instrument Approach Procedures (IAP) SA CAT I, SA CAT II, CAT II, and CAT III, and Manual Flight Control Guidance System operations to landing/head-up display (HUD) to touchdown operation to any airport not included in the list of airports with exclusion and protection zones defined in ISED’s SRSP-520 Issue 3 may be prohibited due to possible interference to Radalt from 5G network resulting in degraded system performance.
2. Night Vision Goggles (NVG) or Night Vision Imaging Systems (NVIS) operations for Rotary Wing aircraft may require a moveable searchlight, which the pilot may need to use to assist in determining height above the ground and rates of closure.
3. Helicopter Offshore RNAV (GNSS)/ARA procedures to a location where 5G in the C-band is deployed may be prohibited in IMC to RA minima because the Radalt may not be reliable. It should be noted that ISED does not have authority to regulate beyond 12 Nm from shore.
4. Helicopters performing takeoffs and landings in accordance with any procedure (Category A, Category B, or by Performance Class in the Rotorcraft Flight Manual or Operations Specification) that requires the use of radio altimeter data may be prohibited because the radio altimeter may not reliable.
5. Helicopter auto hover and engaging Search and Rescue (SAR) autopilot modes that require radio altimeter data may be prohibited because the radio altimeter may not be reliable.
6. International operators may need to be aware of the potential risk of interference to radio altimeters when operating in countries with different 5G networks and their respective mitigations measures that operators are to comply with States Notice To Airmen (NOTAMs) or ADs that may prohibit instrument approach procedure or operation unless alternative methods of compliance (AMOC) are approved.

Ongoing Recommended Action:

1. Operators of aircraft already covered by FAA ADs or by potential aviation limitations specified in Appendix B of this notice are encouraged to proactively plan to retrofit their aircraft to be Radio Altimeter tolerant, where the replication of the FAA Generic Fixed Wing and Rotary Wing restrictions, and aircraft specific restrictions would impact their operations, by securing maintenance slots, parts, and supplemental type certificates (STCs), and adjust accordingly based on final retrofit requirements that will be published.
2. Operators should also continue to follow the Reporting Recommendations in CASA 2021-08. In the event of an actual disturbance of radio altimeter, it is imperative that flight crew report the event to the Air Traffic Service as soon as possible, regardless of the location of the occurrence be it domestic or foreign airspace. Pilot in command and operator are to complete the ‘Radio Altimeter Disturbance/Interference Report’ in Appendix D: Radio Altimeter Disturbance/Interference Report.
3. Transport Canada is committed to ensuring the safety of the aviation system during the deployment of 5G networks while minimizing impacts to the Canadian aviation industry and ensuring aviation safety.
4. Transport Canada continues to engage its United States counterparts as well as its aviation stakeholders to assess existing aviation safety risks in all weather conditions, particularly for aircraft that are equipped with Radio Altimeters that are not 5G-tolerant and develop aviation-side mitigations to safeguard Canada’s aviation system while protecting the continuous flow of air traffic.
5. Aviation safety is paramount to Transport Canada and the department is committed to strengthening Canada’s aviation system and promote aviation safety throughout Canada.

Contact Office :

For more information concerning this issue, contact the AART Documentation Services AARTDocServices-ServicesdocAART@tc.gc.ca.

Original signed by

Charles Lanning
Acting Director, Standards
Civil Aviation

Appendix A: Criteria for Radio Altimeter Tolerance in Canada

In the U.S., these requirements are established in FAA ADs 2023-10-02 (for airplanes) and 2023-11-07 (for rotorcraft). FAA ADs may tailor future 5G-related Canadian ADs.

Potential Canadian Fundamental Emissions Tolerance Requirements

Until ISED 5G protection measures are lifted, alleviation to potential aviation limitations may be as follows:

1. For airplanes operating at the protected runways listed in Appendix C at the 35 airports with exclusion and protection zones: radio altimeters tolerant to the TCCA PSD curves for both 3.45-3.65 GHz, 3.65-3.9 GHz, and 3.9-3.98 GHz (see Figure 1).
   1. General limitations (such as those specified in FAA AD 2023-10-02), and model-specific limitations (such as those specified in TCCA ADs CF-2023-44, CF-2023-47, and multiple FAA ADs affecting Boeing products) are expected to be alleviated.
2. For airplanes operating elsewhere in Canada: radio altimeters meeting the FAA definition of Radio Altimeter Tolerant per FAA AD 2023-10-02.
   1. General limitations (such as those specified in FAA AD 2023-10-02), and model-specific limitations (such as those specified in TCCA ADs CF-2023-44, CF-2023-47, and multiple FAA ADs affecting Boeing products) are expected to be alleviated.
3. For rotorcraft: radio altimeters meeting the FAA definition of Radio Altimeter Tolerant per FAA AD 2023-11-07.
   1. General limitations are expected to be alleviated, such as those indicated in FAA AD 2023-11-07. At this time no model-specific limitations are known to TCCA.

Figure 1: Effective Isotropic Power Spectral Density curves based on height above ground.

January 1^st, 2026 represents a planned sunset date of current spectrum mitigations at which time, Radio Altimeter Tolerant aircraft will require re-evaluation of necessary operational limitations and/or mandatory retrofit requirements.

Appendix B: Examples of aviation limitations

The table below, summarizes and represents a non-exhaustive set of limitations imposed by FAA ADs. For the complete content and in case of any disagreement, refer to the respective AD.

Aircraft Model	FAA Airspace AD	Limitations
Boeing 747-100/-100B/-100B SUD/-200B/-200C/-200F/-300/-400/-400D/-400F	FAA AD 2023-12-14	Operators must use 5G C-Band Interference procedures (AFM) for dispatch or release to airports, and takeoff, approaching, landing, and go-around on runways in the contiguous U.S. airspace (for non-tolerant radio altimeters aeroplanes), unless operating in a 5G mitigate airport (for tolerant radio altimeters aeroplanes).  Some takeoff, approaching, landing, and go-around revised AFM procedures:   Autopilot (AP) may not engage at minimum altitude;   Disconnect Autothrottle (AT) and AP on ILS approaches;   Disengage AT and AP on non-precision approaches before descending below Minimum Decision Altitude (MDA);   Altitude callouts unreliable. Landing distance adjustment (longer landing distance) due to manual speed brake deployment.   Takeoff/Go-around (TO/GA) mode may be unavailable.
Boeing 747-8F/-8 & 777	FAA AD 2023-12-05	Prohibited dispatch or release to airports, and approaches and landings on runways in the contiguous U.S. airspace (for non-tolerant radio altimeters aeroplanes), unless operating in a 5G mitigate airport (for tolerant radio altimeters aeroplanes).
Boeing 757 & 767	FAA AD 2023-12-12	Operators must use 5G C-Band Interference procedures (AFM) for dispatch or release to airports, and approaching, landing, and go-around on runways in the contiguous U.S. airspace (for non-tolerant radio altimeters aeroplanes), unless operating in a 5G mitigate airport (for tolerant radio altimeters aeroplanes).  Some approaching, landing, and go-around revised AFM procedures:  Disconnect AP) and AT prior to performing ILS approaches;  Manual extension of speedbrake if MAX BRAKING is required, and associated landing distance adjustment (longer landing distance);  Cycle flight director during missed approach.
Boeing 707, 717 & 727   DC-8, DC-9 & DC-10   MD-10, MD-11, MD-88 & MD-90	FAA AD 2023-12-15	Operators must use 5G C-Band Interference procedures (AFM) for different flight phases (based on aircraft group) in the contiguous U.S. airspace (for non-tolerant radio altimeters aeroplanes), unless operating in a 5G mitigate airport (for tolerant radio altimeters aeroplanes).  Some revised AFM procedures (differences based on aircraft group): AP and AT disconnected prior to performing ILS approaches;   Manual extension of ground spoilers and associated landing distance adjustment (longer landing distance);   Specific  manual procedures for missed approach instead of automation.
Boeing 737-8/-9/-8200 (MAX)	FAA AD 2023-12-11	Operators must use 5G C-Band Interference procedures (AFM) for dispatch or release to airports, takeoff or landing on runways in the contiguous U.S. airspace (for non-tolerant radio altimeters aeroplanes), unless operating in a 5G mitigate airport (for tolerant radio altimeters aeroplanes).  Some climb-out, descending, landing, and go-around AFM revised procedures:  Prohibit dispatch with certain systems inoperative;  Prohibit landing or takeoff on runways covered in ice or wet ice;  Increase landing distance due to potential effects on systems;  Monitor AT and AP on approach, disconnect if malfunction;  Altitude callouts unavailable or erroneous;  Manually deploy speedbrakes and associated landing distance adjustment (longer landing distance);  TO/GA mode unavailable.
Boeing 737-100 through –900 (ER)	FAA AD 2023-12-13	Operators must use 5G C-Band Interference procedures (AFM) for dispatch or release to airports, and approach, landing and go-around on runways in the contiguous U.S. airspace (for non-tolerant radio altimeters aeroplanes), unless operating in a 5G mitigate airport (for tolerant radio altimeters aeroplanes).  Some approach, landing, and go-around revised AFM procedures (differences based on aircraft group):  Pilots monitor ILS approaches (other than SA CAT I, SA CAT II, CAT II and CAT III) and go-around if certain anomalous behaviour is observed;  Manually deploy speedbrakes and associated landing distance adjustment (longer landing distance);  Do not use Flight Director (FD), AT, AP until at safe altitude on go-around. TOGA mode and AP may not be available.
Boeing 787	FAA AD 2023-12-10	Prohibited to dispatch or release to airports or landing on runways in the contiguous U.S. airspace (for non-tolerant radio altimeters aeroplanes), unless operating in a 5G mitigate airport (for tolerant radio altimeters aeroplanes):  With certain systems inoperative – applicable MEL items.  With a runway condition code of 1 or 0.  Operators must use 5G C-Band Interference procedures (AFM) for dispatch or release to airports or landing on runways in the contiguous U.S. airspace (for non-tolerant radio altimeters aeroplanes), unless operating in a 5G mitigate airport (for tolerant radio altimeters aeroplanes).  Some landing revised AFM procedures:   Landing distance adjustment (longer landing distance) due to manual speed brake deployment.

The table below enumerates the ADs for US airspace imposed by TCCA. Please note that the information provided in the limitations column provides a non-exhaustive summary of limitations. For the complete content and in case of any disagreement, refer to the respective AD.

Also to note, the FAA ADs may tailor future 5G-related Canadian ADs.

Aircraft Model	TCCA Airspace AD	Limitations
Airbus Canada A220-100/300 (BD-500-1A10 & BD-500-1A11)	TCCA AD CF-2023-47	Prohibited to dispatch or release to airports in the contiguous U.S. airspace (for non-tolerant radio altimeters aeroplanes), unless operating in a 5G mitigate airport (for tolerant radio altimeters aeroplanes), with certain systems inoperative – applicable MEL items.
MHI RJ Aviation ULC CL-600-2B19, -2C10, -2C11, -2D15, -2D24, -2E25	TCCA AD CF-2023	No AD limitations, required the installation of a new RF bandpass filter on the coaxial line – recommended mitigations provided in guidance of Flight Operations Notices (FON) related to Potential Unreliable Operation of Radio Altimeter Caused by 5G C-Band Interference.

Appendix C: List of protected runways

Table 1 identifies the runways which, under the current plans are planned to be protected by ISED 5G Protection/Exclusion Zones until at least 31 December 2025 and will provide alleviation to model specific aviation limitations for aircraft considered Radio Altimeter Tolerant, or as per Appendix A, paragraph 1).

Note: Airports indicated in Bold typeface are subject to medium-power deployment in the 3900 MHz band.

Airport Name		Protected Runways
1	Abbotsford International Airport/Aéroport International d'Abbotsford	RWY-07/25
2	Calgary International Airport/Aéroport International de Calgary	RWY-08/26
	Calgary International Airport/Aéroport International de Calgary	RWY-11/29
	Calgary International Airport/Aéroport International de Calgary	RWY-17L/35R
	Calgary International Airport/Aéroport International de Calgary	RWY-17R/35L
3	Charlottetown International Airport/Aéroport International de Charlottetown	RWY-03/21
	Charlottetown International Airport/Aéroport International de Charlottetown	RWY-10/28
4	Churchill Airport/Aéroport de Churchill	RWY-15/33
5	Comox Valley Airport/Aéroport de Comox Valley	RWY-12/30
	Comox Valley Airport/Aéroport de Comox Valley	RWY-18/36
6	Deer Lake Regional Airport/Aéroport Régional de Deer Lake	RWY-07/25
7	Edmonton International Airport/Aéroport International d'Edmonton	RWY-02/20
	Edmonton International Airport/Aéroport International d'Edmonton	RWY-12/30
8	Erik Nielsen Whitehorse International Airport/Aéroport International Erik Nielsen de Whitehorse	RWY-14R/32L
9	Fort McMurray International Airport/Aéroport International de Fort McMurray	RWY-08/26
10	Fredericton International Airport/Aéroport International de Fredericton	RWY-09/27
	Fredericton International Airport/Aéroport International de Fredericton	RWY-15/33
11	Gander International Airport/Aéroport International de Gander	RWY-03/21
	Gander International Airport/Aéroport International de Gander	RWY-13/31
12	Goose Bay Airport/Aéroport de Goose Bay	RWY-08/26
	Goose Bay Airport/Aéroport de Goose Bay	RWY-15/33
13	Greater Moncton Roméo LeBlanc International Airport /Aéroport International Romèo LeBlanc du Grand Moncton	RWY-06/24
	Greater Moncton Roméo LeBlanc International Airport /Aéroport International Romèo LeBlanc du Grand Moncton	RWY-11/29
14	Halifax Stanfield International Airport/Aéroport International de Halifax	RWY-05/23
	Halifax Stanfield International Airport/Aéroport International de Halifax	RWY-14/32
15	Iqaluit Airport/Aéroport d'Iqualuit	RWY-16/34
16	J.A. Douglas McCurdy Sydney Airport/Aéroport de Sydney J.A. Douglas McCurdy	RWY-06/24
	J.A. Douglas McCurdy Sydney Airport/Aéroport de Sydney J.A. Douglas McCurdy	RWY-18/36
17	John C. Munro Hamilton International Airport /Aéroport International John C. Munro d'Hamilton	RWY-06/24
	John C. Munro Hamilton International Airport /Aéroport International John C. Munro d'Hamilton	RWY-12/30
18	Kelowna International Airport/Aéroport International de Kelowna	RWY-16/34
19	London International Airport/Aéroport International de London	RWY-09/27
	London International Airport/Aéroport International de London	RWY-15/33
20	Mirabel International Airport/Aérocité Internationale de Mirabel	RWY-06/24
	Mirabel International Airport/Aérocité Internationale de Mirabel	RWY-11/29
21	Montréal-Pierre Elliott Trudeau International Airport/Aéroport International Pierre Elliott Trudeau de Montréal	RWY-06L/24R
	Montréal-Pierre Elliott Trudeau International Airport/Aéroport International Pierre Elliott Trudeau de Montréal	RWY-06R/24L
	Montréal-Pierre Elliott Trudeau International Airport/Aéroport International Pierre Elliott Trudeau de Montréal	RWY-10/28
22	North Bay Jack Garland Airport/Aéroport North Bay Jack Garland	RWY-08/26
23	Ottawa International Airport/Aéroport International d'Ottawa	RWY-07/25
	Ottawa International Airport/Aéroport International d'Ottawa	RWY-14/32
24	Prince George Airport/Aéroport International de Prince George	RWY-06/24
	Prince George Airport/Aéroport International de Prince George	RWY-15/33
25	Québec City Jean Lesage International Airport/Aéroport International Jean-Lesage de Québec	RWY-06/24
	Québec City Jean Lesage International Airport/Aéroport International Jean-Lesage de Québec	RWY-11/29
26	Regina International Airport/Aéroport International de Regina	RWY-08/26
	Regina International Airport/Aéroport International de Regina	RWY-13/31
27	Saskatoon John G. Diefenbaker International Airport/Aéroport International John G. Diefenbaker de Saskatoon	RWY-09/27
	Saskatoon John G. Diefenbaker International Airport/Aéroport International John G. Diefenbaker de Saskatoon	RWY-15/33
28	St. John’s International Airport/Aéroport International de St. John's	RWY-02/20
	St. John’s International Airport/Aéroport International de St. John's	RWY-11/29
	St. John’s International Airport/Aéroport International de St. John's	RWY-16/34
29	Stephenville Dymond International Airport/Aéroport International Stephenville Dymond	RWY-09/27
30	Thunder Bay International Airport/Aéroport International de Thunder Bay	RWY-07/25
	Thunder Bay International Airport/Aéroport International de Thunder Bay	RWY-12/30
31	Toronto Pearson International Airport/Aéroport International Pearson Toronto	RWY-05/23
	Toronto Pearson International Airport/Aéroport International Pearson Toronto	RWY-06L/24R
	Toronto Pearson International Airport/Aéroport International Pearson Toronto	RWY-06R/24L
	Toronto Pearson International Airport/Aéroport International Pearson Toronto	RWY-15L/33R
	Toronto Pearson International Airport/Aéroport International Pearson Toronto	RWY-15R/33L
32	Vancouver International Airport/Aéroport International de Vancouver	RWY-08L/26R
	Vancouver International Airport/Aéroport International de Vancouver	RWY-08R/26L
	Vancouver International Airport/Aéroport International de Vancouver	RWY-13/31
33	Victoria International Airport/Aéroport International de Victoria	RWY-03/21
	Victoria International Airport/Aéroport International de Victoria	RWY-09/27
	Victoria International Airport/Aéroport International de Victoria	RWY-14/32
34	Winnipeg James Armstrong Richardson International Airport/Aéroport International James Armstrong Richardson de Winnipeg	RWY-13/31
	Winnipeg James Armstrong Richardson International Airport/Aéroport International James Armstrong Richardson de Winnipeg	RWY-18/36
35	Yellowknife Airport/Aéroport de Yellowknife	RWY-10/28
	Yellowknife Airport/Aéroport de Yellowknife	RWY-16/34

Appendix D: Radio Altimeter Disturbance/Interference Report

Available online:

https://wwwapps.tc.gc.ca/Corp-Serv-Gen/5/forms-formulaires/searchrs.aspx?formnumber=26-0870