2-7 Note: In some countries, ICAO Annex 6 fuel SARPs are in force, which may be more restrictive than applicable 14 CFR rules.
2.3.6 Overwater Airspaces and Interrelationships. Table 2-2 below provides a summary of the various overwater airspaces and their interrelationships.
Table 2-2. Overwater Airspaces and Interrelationships Type of Airspace High-Level Definition Remarks/Relationship to Other Airspaces U.S. sovereign airspace Airspace over land or 12 NM or less from the coast of the United States.
Part 91 subpart B applies.
High seas airspace Airspace beyond 12 NM from the coast.
ICAO Annex 2 applies.
Offshore airspace International (high seas) airspace over water where VHF voice and ATS surveillance (radar and/or Automatic Dependent Surveillance-Broadcast (ADS-B)) coverage exist.
• Begins beyond 12 NM from the coast (high seas).
• Usually extends to ~175 NM from the coast.
• Normally has a boundary with an OCA.
• Does not include OCAs where LRCS are used.
Oceanic Control Area (OCA) Flight information regions (FIR) where LRCS are required.
Extended overwater operations (14 CFR § 1.1) Operations greater than 50 NM from the nearest shoreline.
For certificated operators, 14 CFR requirements on emergency equipment and communication and navigation equipment apply.
2.3.6.1 Other distances generally relevant to oceanic flying are:
2.3.6.1.1 A VOR/DME with “High Altitude” (H) standard service volume (SSV) classification has a range of 130 NM. Coastal areas generally have a good network of VOR/DMEs of the (H) SSV classification.
2.3.6.1.2 The typical maximum range for the Air Traffic Service (ATS) surveillance systems (e.g., radar and ADS-B) and VHF voice transceivers is 150–200 NM.
For this reason, OCAs typically begin approximately 175 NM from the coast.
2.4 Differing Airspace Requirements. It is quite possible to transit regions with significantly different procedures in one long-range flight. Therefore, you should familiarize yourself with the equipment and procedural requirements to file and fly in each segment of foreign
2-8 airspace in which you intend to operate by referencing, for example, the appropriate State’s AIP.
2.5 Operational Authorizations.
2.5.1 Title 14 CFR part 91 operators need LOA B036, Oceanic Required Navigation Performance (RNP) Operations, to indicate oceanic RNP on ATC flight plans. Further discussion on other 14 CFR part 91 LOAs and the application process are in Appendix B, Operational Authorizations: 14 CFR Part 91 LOAs.
2.5.2 Certificated operators (14 CFR parts 121, 125, 121/135, and 135) require OpSpecs, MSpecs, and/or 14 CFR part 125 LOAs. Further information on oceanic and remote continental authorizations for certificated operators is available from the responsible Flight Standards office.
2.6 ICAO Guidance Documents and Reference Material. Find the following ICAO documents at the ICAO store at https://store.icao.int or at the ICAO eLibrary at https://elibrary.icao.int.
2.6.1 Guidance Documents. We developed much of the material in this AC from these foundational documents: ICAO Annexes, other ICAO guidance documents, related sections of 14 CFR, and other FAA guidance material.
2.6.2 Chicago Convention. We single out the following articles of the Convention on International Civil Aviation (listed in ICAO Doc 7300, Convention on International Civil Aviation) because of their importance in regulating international aviation. If you operate in oceanic and remote continental airspace, you should thoroughly understand them.
• Article 1, Sovereignty.
• Article 12, Rules of the Air.
• Article 29, Documents Carried in Aircraft.
2.6.3 ICAO Publications. The principal purpose of ICAO publications is the “systematic and prompt dissemination in concise form of the policies and activities of the Organization.”
These publications consist of Annexes, documents with “Procedures for Air Navigation Services” and “Regional Supplementary Procedures” in the name, manuals, and other similar publications. The following is a brief description of each category of publications, beginning with the most authoritative, and moving down the hierarchy.
2.6.3.1 Annexes. There are 19 Annexes (named in paragraph 2.2 above) to the Convention on International Civil Aviation (listed in ICAO Doc 7300). They state the SARPs.
2.6.3.2 Procedures for Air Navigation Services (PANS) and Regional Supplementary Procedures (SUPPS). ICAO publications with “Procedures for Air Navigation Services” in the title have special status, as does the publication “Regional Supplementary Procedures.”
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2.6.3.2.1 ICAO Doc 4444, Procedures for Air Navigation Services—Air Traffic Management (PANS-ATM). These procedures complement the SARPs contained in ICAO Annexes 2 and 11, and specify, in greater detail than in the SARPs, the actual procedures ATS units apply when providing various services to air traffic. ICAO Doc 4444 is the primary reference for oceanic contingency procedures, described in Appendix F, Special Procedures for In-Flight Contingencies in Oceanic Airspace.
2.6.3.2.2 ICAO Doc 8168, Procedures for Air Navigation Services—Aircraft Operations (PANS-OPS). This document has three volumes:
1. Volume I, Flight Procedures, describes operational requirements for flying the procedures designed in accordance with the criteria provided in Volume II.
2. Volume II, Construction of Visual and Instrumental Flight Procedures, is intended for the guidance of procedures specialists and describes the essential areas and obstacle clearance requirements for the achievement of safe, regular instrument flight operations. It provides the basic guidelines to States, and those operators and organizations producing instrument flight charts, that will result in uniform practices at all aerodromes where instrument flight procedures are carried out.
3. Volume III, Aircraft Operating Procedures, describes operational procedures recommended for the guidance of flight operations personnel and flightcrew.
2.6.3.2.3 ICAO Doc 7030, Regional Supplementary Procedures. For each ICAO region, ICAO Doc 7030 provides detailed procedures designed to meet those needs of specific areas that are not covered in the worldwide provisions contained in the Annexes and PANS documents. The SUPPS complement the statement of requirements for facilities and services contained in the Air Navigation Plan publications.
Note: To illustrate the hierarchy among ICAO publications, we can look at the topic of communication failure. ICAO Annex 2 details global procedures on communication failure. ICAO Doc 4444 elaborates on those procedures, which, “unless otherwise prescribed on the basis of regional air navigation agreement,” are in effect.
ICAO Doc 7030 describes such regional agreements (e.g., area-specific communication failure procedures). FAA principal inspectors (PI) and specialists within the FAA’s Flight Technologies and Procedures Division, Flight Operations Group can help you understand the relationship between various ICAO publications.
2.6.3.3 Manuals. Similar to our ACs, ICAO manuals provide guidance and information concerning selected aspects of aeronautical activity or facilitating the uniform application of ICAO SARPs. Therefore, you should familiarize
2-10 yourself with the following documents (current editions) prior to undertaking operations in oceanic and remote continental airspace. The following are the more prominent ICAO manuals:
2.6.3.3.1 ICAO Doc 9574, Manual on a 300 m (1,000 ft) Vertical Separation Minimum Between FL 290 and FL 410 Inclusive. ICAO Doc 9574 provides States’ regional planning groups with a basis for the revision of documents, procedures, and programs to enable the maintenance of a 300 m (1,000 ft) vertical separation minimum between flight level (FL) 290 and FL 410 inclusive, in accordance with the criteria and requirements developed by ICAO. It provides guidance to State aviation authorities on those measures necessary to ensure that the criteria and requirements are met within their area of responsibility, as well as background information for operators to assist in the development of operating manuals and flightcrew procedures.
2.6.3.3.2 ICAO Doc 9613, Performance-based Navigation (PBN) Manual. This manual provides practical guidance on how to implement Area Navigation (RNAV) and Required Navigation Performance (RNP) applications, and how to ensure that the performance requirements are appropriate for the planned application.
2.6.3.3.3 ICAO Doc 9869, Performance-based Communication and Surveillance (PBCS) Manual. This guidance material explains the concepts of Required Communication Performance (RCP) and Required Surveillance Performance (RSP), identifies RCP and RSP requirements applicable to the provision and use of ATS, and provides a basis for the application of RCP and RSP in a specified airspace.
2.6.3.3.4 ICAO Doc 10037, Global Operational Data Link (GOLD) Manual. The GOLD Manual addresses data link service provision, operator readiness, controller and flightcrew procedures, performance-based specifications, and post-implementation monitoring and analysis. GOLD provides guidance and information concerning data link operations and is intended to facilitate the uniform application of ICAO SARPs contained in ICAO Annexes 2, 10, and 11; the provisions in ICAO Doc 4444; and, when necessary, ICAO Doc 7030.
2.6.3.3.5 ICAO NAT Doc 007, North Atlantic Operations and Airspace Manual. This document provides information for aircraft operating agencies, pilots, and dispatchers planning and conducting operations in or above the North Atlantic High Level Airspace (NAT HLA). It also offers guidance to the State regulators responsible for the approval/certification/licensing of such aircraft operators, pilots, or dispatchers.
Note: Operators flying below NAT HLA should pay particular attention to ICAO NAT Doc 007 guidance on flight operations below the NAT HLA.
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2.6.4 Other References:
1. ICAO Satellite Voice Guidance Material (SVGM), available at https://www.icao.int/apac/documents/edocs/cns/satvoice_svgm_v1.pdf. This document is intended to maximize the operational benefits of Satellite Voice (SATVOICE) implementations by promoting seamless and interoperable SATVOICE operations throughout the world. The document provides guidance and information concerning SATVOICE communications for aeronautical use and is intended to facilitate the uniform application of ICAO SARPs contained in ICAO Annex 2, the provisions in ICAO Doc 4444, and, when necessary, ICAO Doc 7030.
2. The FAA website at https://www.faa.gov.
3. Regional Oceanic Resource Guides for U.S. Operators, available at https://www.faa.gov/about/officeorg/headquartersoffices/avs/oceanic-resourceguides.
Note: Contact information for specialists from the Flight Operations Group can be obtained from the responsible Flight Standards office and is available in these resource guides.
4. Applicable FAA Domestic/International Notices and Notices to Airmen (NOTAM).
5. U.S. AIP and applicable foreign AIPs. The AIP is the State’s official publication that defines and describes the airspace, aeronautical facilities, services, and national rules and practices pertaining to air traffic, particularly if they differ from ICAO SARPs (“differences” are listed in AIPs). Eurocontrol maintains a global listing of links to AIPs at https://eurocontrol.int/articles/ais-online. Refer to the current AIP for any States whose airspace you intend to operate in/through.
6. Regulations of the foreign countries over which you intend to fly.
7. The customs procedures, cultural considerations, entry and overflight procedures, and health and safety precautions for each country in which you intend to land.
8. The “Oceanic and Remote” section of the FAA’s Flight Operations Group web page at https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/afx/afs/afs4 00/afs410/oceanic_remote. Refer in particular to the “Oceanic and Remote Continental Application Guides” posted there.
9. The “Data Communications” section of the FAA’s Flight Operations Group web page at https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/af x/afs/afs400/afs410/datacomm/. Refer in particular to the “Data Link Communication Application Guide” posted there.
10. NAT bulletins, found in the “EUR and NAT Documents” area of the ICAO website:
https://www.icao.int/EURNAT/Pages/EUR-and-NAT-Document.aspx.
11. The NAT Central Monitoring Agency (CMA). The NAT CMA hosts a secure site with event reports and summaries at https://natcma.com. Industry stakeholders can request access to deidentified reports.
3-1 CHAPTER 3. PILOT QUALIFICATION AND TRAINING GUIDANCE FOR OCEANIC
AND REMOTE CONTINENTAL AIRSPACE OPERATIONS
3.1 Training Requirements for Oceanic and Remote Continental Airspace Operations.
3.1.1 Certificated Operator Training. Certificated operators are required to have training approved by the Administrator.6 This normally takes place during the certification process and prior to issuance of operational authorizations.
6 References are 14 CFR §§ 91.1073, 121.401, 125.296, and 135.323.
3.1.2 General Aviation (GA) Training. If you are a GA pilot desiring to indicate oceanic Required Navigation Performance (RNP) capability, you need operational authorization via an LOA B036 (see Appendix B, Operational Authorizations: 14 CFR Part 91 LOAs, paragraph B.1).7 An optional LOA B030 is available for Remote Continental operations.
The following are options for training:
7 Regulatory reference is 14 CFR § 91.703, which incorporates ICAO Annex 2 by reference. Annex 2, in turn, refers to ICAO Doc 7030, which requires State of the Operator or State of Registry approval for oceanic RNP operations.
1. Comple ting an operator’s oceanic operations current training program.
2. Completing a commercial oceanic operations current training program.
3. Submitting military training records indicating prior oceanic operations experience.
4. Using other methods indicating that you can safely conduct oceanic operations.
Examples could include written testing, oral testing, or evidence of prior recent experience.
3.1.3 Relevant Subject Matter. The following items are examples of the subject matter with which you should be familiar in order to conduct operations in oceanic and remote continental airspace (as required based on the types of operations being conducted):
1. Title 14 CFR (applicable parts).
2. ICAO Standards and Recommended Practices (SARPs) and measurement standards.
3. Operator’s international operating procedures, to include the international operations manual,8 its organization and structure, and access via Electronic Flight Bag (EFB), as applicable.
8 See also Appendix G, Suggested Subjects for Inclusion in Oceanic and International Procedures and/or an Operations Manual.
4. Use of oceanic flight planning charts.
5. Sources and content of international flight publications.
6. Itinerary planning and overflight clearances.
7. Meteorology, including Significant Weather (SIGWX) charts, prognostic weather charts, tropopause prognostic charts, and Terminal Aerodrome Forecasts (TAF), as well as space weather.
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8. Preparation of international flight plans, plotting charts, and operational flight plans/flight logs, to include Equal Time Point (ETP) calculations. These include the communications, navigation, and surveillance capability codes appropriate to your aircraft and your operational authorization.
9. Specific airspace requirements, to include communications, navigation, and surveillance equipment requirements and operational authorizations, as well as operational procedures related to Reduced Vertical Separation Minimum (RVSM) and RNP.
10. Long-range, air-to-ground communication procedures, including all data link and satellite communications (SATCOM) voice operations, as applicable.
11. En route and terminal procedures—differences from U.S. procedures.
12. Use of oceanic checklists.
13. Oceanic error risk mitigations.
14. Understanding of Strategic Lateral Offset Procedures (SLOP).
15. Air traffic clearances, to include proper terminology and phraseology.
16. Emergency and contingency procedures (see Appendix F, Special Procedures for In-Flight Contingencies in Oceanic Airspace), including contingency procedures for weather divisions, required emergency equipment, Search and Rescue (SAR) techniques, communication failure procedures, and navigation equipment failure techniques (to include dead reckoning).
17. Specialized training (e.g., if conducting operations in areas of magnetic unreliability (AMU), or, for 14 CFR parts 121 and 135, Extended Operations (ETOPS) “preclude and protect” philosophy, as applicable).
18. Use of polar/remote area checklists.
19. Polar/remote continental terrain awareness, risk mitigations, and contingency options.
4-1 CHAPTER 4. COMMUNICATIONS, NAVIGATION, AND SURVEILLANCE
SYSTEMS GUIDANCE FOR OPERATIONS IN OCEANIC AND REMOTE
CONTINENTAL AIRSPACE
4.1 Communications, Navigation, and Surveillance Improvements—Impact on Air Traffic Service (ATS).
4.1.1 Technological Advances. Technological advances in communications, navigation, and surveillance systems all contribute to an air traffic system that provides increased navigational accuracy and allows you and your aircraft to interact more quickly with controllers. These advances have also improved controller-pilot communications, navigation accuracy, and aircraft surveillance reporting. This enhanced communications, navigation, and surveillance capability greatly reduces the errors and retransmissions that hampered oceanic flights just a few years ago. These safety improvements have facilitated corresponding improvements in efficiency and capacity by reducing separation minima, allowing controllers to space aircraft closer together. Trials of new separation minima or implementations of new operating procedures are common in oceanic airspace. Operators should therefore make sure they have the most up-to-date information concerning the airspace in which they will be flying. U.S. and foreign State Aeronautical Information Publications (AIP), Notices to Airmen (NOTAM), and related publications are normally the best sources of current information. International operations manuals that consolidate this information should be current.
4.1.2 Automatic Dependent Surveillance-Broadcast (ADS-B). ADS-B supports these improvements by providing a higher update and enhanced accuracy of surveillance information over the current radar-based surveillance systems.
4.1.3 Space-Based ADS-B. In 2019, a constellation of low-Earth orbit satellites with ADS-B receivers began supplying surveillance data to ATS Providers (ATSP). Shortly thereafter, ICAO published a new separation standard for areas under ADS-B surveillance where very high frequency (VHF) voice communications are not available. This new separation standard allows aircraft to be more closely spaced in oceanic areas, which in turn allows more efficient routing. While space-based ADS-B update rates are comparable to those of some domestic radar systems, communication systems traditionally used in oceanic and remote continental airspace do not perform as quickly as the VHF voice communications used in domestic environments. Consequently, aircraft cannot yet be spaced as closely as in domestic areas. As communication systems evolve, allowable separation between aircraft will likely be reduced further.
4.2 Performance-Based Operations.
4.2.1 Performance Specifications. The three performance specifications, Required Communication Performance (RCP), Required Navigation Performance (RNP), and Required Surveillance Performance (RSP), determine required separation between flights.
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4.2.2 RCP. RCP establishes aircraft/controller communications timeline, safety, equipment, and flightcrew training standards. Generally, RCP is specified in terms of the timeline required to complete the communication transaction and the continuity, availability, and integrity of the transaction. In addition, RCP includes criteria for monitoring and alerting.
In oceanic and remote continental airspace, RCP 240 and RCP 400 are the relevant communications-related performance specifications.
4.2.2.1 RCP 240 requires a 99.9 percent probability (continuity) the communications transaction will complete in less than 240 seconds (timeline). It also requires a
99.99 percent probability the communication can be initiated (availability) and no more than 10-5 communications transaction malfunctions per flight-hour (integrity).
9 RTCA DO-350B, published in September 2023, relaxed the availability requirement to 99.8 percent. As of early 2025, ICAO Doc 9869 Second Ed ition was still current and listed the RCP 240 requirement for availability as
99.9 percent.
4.2.2.2 RCP 400 requires a 99.9 percent probability (continuity) the communications transaction will complete in less than 400 seconds (timeline). It also requires a
99.910 percent probability the communication can be initiated (availability) and no more than 10-5 communications transaction malfunctions per flighthour (integrity).
10 RTCA DO-350B, published in September 2023, relaxed the availability requirement to 99.8 percent. As of early 2025, ICAO Doc 9869 Second Edition was still current and listed the RCP 400 requirement for availability as
99.9 percent.
4.2.2.3 U.S. ope rators desiring Performance-based Communication and Surveillance (PBCS) approval for qualifying systems (e.g., with RCP 240 and RSP 180) can obtain the A056 authorization. See paragraph 4.5 below.
4.2.2.4 For additional details, please refer to AC 90-117, Data Link Communications;
and ICAO Doc 10037, Global Operational Data Link (GOLD) Manual, and ICAO Doc 9869, Performance-based Communication and Surveillance (PBCS) Manual, Appendix B, RCP Specifications, at https://store.icao.int.
4.2.3 RNP. RNP establishes aircraft navigation accuracy, equipment, and flightcrew training standards. In addition, RNP includes criteria for monitoring and alerting. ICAO Doc 9613, Performance-based Navigation (PBN) Manual, outlines these standards.
Generally, we measure these standards in terms of accuracy, integrity, continuity, availability, and functionality. Oceanic and remote continental airspace ATSPs primarily provide RNP 10 (also known as Area Navigation (RNAV) 10) and RNP 4-based separation minima. RNP 2 applications have also become available for oceanic and remote continental airspace, to be used by individual States as necessary to meet their airspace requirements. In all cases, ATSPs will apply appropriate separation minima between adjacent aircraft based on the capabilities each aircraft operator files in the flight
4-3 plan. You must only indicate the oceanic RNP capability authorized in your B036 authorization.11 11 Regulatory reference is 14 CFR § 91.169, which refers to 14 CFR § 91.153. This requires the flight plan to include “any other information the pilot in command or ATC believes is necessary for ATC purposes.”
1. RNP 10 r equires accuracy to be within 10 nautical miles (NM) 95 percent of the time.
2. RNP 4 requires accuracy to be within 4 NM 95 percent of the time and within 8 NM
99.999 percent of the time.
3. RNP 2 requires accuracy to be within 2 NM 95 percent of the time and within 4 NM
99.999 percent of the time.
Note: Regardless of RNP value, pilots are expected to fly the centerline (or where use of Strategic Lateral Offset Procedures (SLOP) is authorized, up to 2 NM right of course).
4.2.4 RSP. RSP establishes aircraft/controller surveillance timeline, safety, and equipment standards. Generally, RSP is specified in terms of the timeline required to complete the transaction and the continuity, availability, and integrity of the transaction. In addition, RSP includes criteria for monitoring and alerting. In oceanic and remote continental airspace, RSP 180 and RSP 400 are the relevant performance specifications.
4.2.4.1 RSP 180 requires a 99.9 percent probability (continuity) the surveillance transaction will complete in less than 180 seconds (timeline). It also requires a
99.912 percent probability the communication can be initiated (availability) and no more than 10-5 communications transaction malfunctions per flight-hour (integrity).
12 RTCA DO-350B, published in September 2023, relaxed the availability requirement to 99.8 percent. As of early 2025, ICAO Doc 9869 Second Edition was still current and listed the RSP 180 requirement for availability as
99.9 percent.
4.2.4.2 RSP 400 r equires a 99.9 percent probability (continuity) the surveillance transaction will complete in less than 400 seconds (timeline). It also requires a
99.913 percent probability the communication can be initiated (availability) and no more than 10-5 communications transaction malfunctions per flight-hour (integrity).
13 RTCA DO-350B, published in September 2023, relaxed the availability requirement to 99.8 percent. As of early 2025, ICAO Doc 9869 Second Edition was still current and listed the RSP 400 requirement for availability as
99.9 percent.
4.2.4.3 For addi tional details, please refer to ICAO Doc 9869.
4.2.5 Access to Performance-Based Separation. Communications, navigation, and surveillance capabilities of aircraft and crew determine eligibility for operational authorizations, which in turn allow operators to take advantage of performance-based separation in oceanic and remote continental airspace. The significant improvements in communications, navigation, and surveillance systems have allowed air traffic controllers
4-4 to reduce separation between aircraft, expanding access to more favorable routing and/or altitudes that offer savings in time and fuel.
4.3 Voice Communications in Oceanic Airspace. When operating over the high seas, ICAO Annex 2, Rules of the Air, requires you to maintain a continuous air-to-ground voice communication watch with the appropriate ATS authority on the appropriate communication channel.
Note: It is not acceptable to depend solely on other aircraft providing a radio relay to satisfy this requirement. The appropriate authority for the airspace where you conduct the flight may prescribe the aeronautical stations and frequencies used for two-way communications.
4.3.1 High Frequency (HF) Radio Communications. HF radios have been in use for almost a century over oceanic and remote continental areas. As technological advances lead to more sophisticated methods of communication, HF equipment has also improved. HF radios now offer digital tuning, compact size, selective calling systems (SELCAL) (see paragraph 4.3.2 below), and new antenna concepts. Consider the following when using HF communications:
4.3.1.1 HF radio calls are typically made to a radio operator, who in turn electronically relays the information, via keyboard and preformatted messages, to air traffic controllers in oceanic centers. There is some delay between your requests and air traffic control (ATC) clearances, where the radio operator coordinates with the appropriate controller. Radio operators do not have the authority to issue ATC clearances on their own.
4.3.1.2 Communications over HF radio rely heavily on proper radio terminology and scripted reports. Use the published guidance found in enroute publications or the Aeronautical Information Manual (AIM) to make sure you deliver messages in the proper format. Speak at a moderate speed using the internationally accepted phraseology. You may find ICAO standard phraseology in ICAO Doc 9432, Manual of Radiotelephony. This document and other ICAO reference materials are available on ICAO’s website at https://store.icao.int.
4.3.1.3 If ATC uses the terms “expect” or “when can you accept,” they have not granted you a clearance. Typically, oceanic radio operators will use the phraseology “ATC clears…” when relaying a clearance.
4.3.1.4 ICAO Doc 4444, Procedures for Air Navigation Services—Air Traffic Management (PANS-ATM), requires the flightcrew to read back level instructions, heading and speed instructions, and ATC route clearances.
Ensure that the radio operator acknowledges your exact read back to confirm that you correctly heard the instructions.
4.3.1.5 In general, higher frequencies (above 10.0 megahertz (MHz)) work better during daylight and lower frequencies (below 10.0 MHz) at night. It is
4-5 common to use several frequencies on one flight while communicating with the same ATSP.
4.3.1.6 HF communications are dependent on transmitted signals striking the ionosphere and reflecting back to antennae at ground stations. The ionosphere is susceptible to interference from space weather, resulting in periods where HF reception is marginal or unreadable. You may especially notice this phenomenon in polar regions above 60° N or below 60° S and during periods of significant solar activity.
4.3.2 SELCAL. SELCAL is a means to alert an individual aircraft that a ground station wishes to communicate with it. ATSPs can transmit SELCAL signals over VHF or HF. The signals produce an audio tone and possibly a cockpit indication that alerts you to initiate contact with the appropriate ATC unit.
4.3.2.1 The SELCAL codes are controlled by a commercial service and are assigned to a specific aircraft. Since the number of unique SELCAL 16-tone codes is less than the number of aircraft with SELCAL capability, multiple aircraft could be operating and logged in with the same SELCAL code assignment.
4.3.2.2 When you apply for SELCAL codes for your aircraft, the issuing company will deconflict duplicate codes by region as much as possible. However, aircraft flying in multiple regions may encounter another aircraft using the same code. Therefore, you should be certain that the ATS radio operator uses your exact call sign when responding to a SELCAL.
4.3.2.3 New SELCALs use 32 tones, instead of only 16 tones currently used, and thereby increase the number of unique identifiers exponentially. The ICAO Communication Panel approved the global implementation of SELCAL 32 for revisions to take effect in November 2022. SELCAL 32 compliant equipment became available beginning in 2020. Operators with 16-tone HF SELCALs may continue to encounter a duplicate code situation.
4.3.2.4 Check HF SELCAL even when your Controller-Pilot Data Link Communications (CPDLC) are working properly. You should do a SELCAL check prior to oceanic entry and then again at each control area (CTA) boundary. See the sample transcript of an HF SELCAL check below.
Sample Transcript of HF SELCAL Check HF call from the air: “New York Radio, Airline 123, request SELCAL Check.”
Answer from the ground:
“Airline 123, New York Radio, roger.”
[SELCAL tones transmitted] HF call from the air: [If successful] “SELCAL okay.”