AC 91-70B

Historical

Advisory circular · Oceanic and Remote Continental Airspace Operations

A newer version is currentThis is a historical version. AC 91-70D is the version in force, approved April 3, 2025.
Approved
October 4, 2016
Last reviewed
August 2, 2024
Cancels
AC91-70A
Cancelled by
AC91-70B CHG 1
Family
AC 91-70 · 6 versions
Revision
B
14 CFR parts
91, 119, 121, 125, 135

Guidance, not mandatory unless a rule or AD requires it. DRS record last changed November 21, 2025.

Show pages 43–54

6.3.2.8.3 You typically enter your FLT ID through either an FMS interface or your transponder control panel. For ATC systems to function correctly, you must ensure the FLT ID you enter in the FMS exactly matches the ACID in block 7 of your international flight plan.

6.3.2.9 Check your ground speed in the blocks and on taxi out.

1. If you are still in the blocks and your ground speed reads other than zero (0), you may have a developing error in your LRNS.

2. Similarly, if your groundspeed on taxi out appears unreasonable, this may also indicate a problem with your LRNS.

6.3.2.10 Accomplish required Reduced Vertical Separation Minimum (RVSM) altimetry ground checks.

6.3.2.10.1 Before taxi, set your altimeters to the airport local altimeter setting. Both primary altimeters must read within ± 75 feet of field elevation.

6.3.2.10.2 The two primary altimeters must also agree with each other within the limits noted in the aircraft operating manual.

6.4 En Route Guidance.

6.4.1 Oceanic Clearance: How to Request, Receive, and Process.

6.4.1.1 Oceanic clearances are unique clearances that frequently require coordination between two or more air traffic agencies. The clearance you receive from an ATC facility on the ground before departure may not constitute a clearance into or through your filed oceanic and remote continental airspace. Depending on the first oceanic FIR you enter, you may need to obtain this clearance separately and specifically as you approach the oceanic and remote continental airspace boundary. Check the Aeronautical Information Publication (AIP) or source document to determine if such separate oceanic clearance is required.

6.4.1.2 In cases when your departure airport is close to the oceanic and remote continental airspace boundary you may, and at some airports must, obtain your oceanic clearance prior to departure. Check the AIP or source documents to determine clearance requirements unique to your departure airport.

Note: Some airspace authorities have begun issuing the route portion of the oceanic clearance before the aircraft departs, even when the departure airport is not close to the oceanic boundary. In this case, the altitude and airspeed portion will be assigned prior to entering oceanic airspace. New York Oceanic and Oakland Oceanic both operate in this manner.

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6.4.1.3 In most cases, obtain your oceanic clearance via voice at least 40 minutes prior to entry, or 30 to 90 minutes prior if using the Aircraft Communications Addressing and Reporting System (ACARS) data link Oceanic Clearance Delivery (OCD) to receive the clearance. As discussed above, if your departure point is close to the oceanic and remote continental airspace boundary, you may be able to obtain your clearance prior to departure.

6.4.1.4 At least two pilots should be involved in the clearance receipt and read back process, one actively obtaining the clearance and the other monitoring.

We recommend both pilots be on a headset during this process.

6.4.1.5 Both pilots should independently copy the clearance. Each pilot cross-checks and verifies both the routing, altitudes, and Mach number assigned (if applicable) for the crossing.

6.4.1.5.1 Read all waypoint coordinates back to the ATS provider in detail. Sometimes, approved local procedures make full read back optional. Always cross-check each detail of the clearance with your master document.

6.4.1.5.2 Ensure the ATS provider acknowledges your correct read back.

6.4.1.5.3 The use of terms “expect” or “when can you accept” by ATC are not a clearance. Typical ATC clearance phraseology is “ATC clears….”

6.4.1.5.4 After each pilot conducts an independent review and verification of the clearance, the crew should discuss the clearance to verify a common understanding and make any plans resulting from the clearance.

6.4.1.6 Ensure the following upon receipt of a reclearance:

Note: A reclearance (that is, a clearance that differs from the oceanic route requested with the filed flight plan) is the number one scenario leading to pilot deviation from the assigned routing. You should be particularly cautious when receiving a reclearance.

6.4.1.6.1 At least two pilots should separately copy the clearance from the ATS provider. Each pilot should be on a headset.

6.4.1.6.2 You read it back correctly and receive an acknowledgement of your read back from the ATS provider.

6.4.1.6.3 All pilots compare the clearance they just copied; contact the ATS provider for clarification of any inconsistencies.

6.4.1.6.4 One pilot reprograms the FMS (or other LRNS), updates the master document, and updates the plotting/orientation chart.

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6.4.1.6.5 A second pilot cross-checks the newly effective route clearance with the reprogrammed route loaded into the FMS, the updated master document, and the updated plotting/orientation chart.

1. The cross-check of the FMS coordinates includes comparing the expanded coordinates (i.e., degrees and minutes).

2. Course and distance connecting the new waypoints should also be checked. Course and distance tables are available commercially for every 10° of longitude, or dispatch can send a new operational flight plan/master document with the updated track and distances.

It is also possible to use an onboard flight planning system to independently calculate course and distance, and check that against the FMS.

6.4.1.6.6 If the clearance is received via Controller-Pilot Data Link Communication (CPDLC), each pilot should read it silently to develop an independent understanding of the new clearance; they should then discuss the clearance and query the controller for clarification if they have any disagreement as to what the clearance is asking them to do.

Note 1: If you “accept” a clearance via CPDLC, the FAA recommends you also “execute” the new clearance in your FMS. Some crews have accepted, but not executed, a CPDLC clearance to avoid losing wind data or to preserve meaningful waypoint labels. Failure to “execute” the new clearance in the FMS could result in a navigation error and/or pilot deviation.

Note 2: Reclearance via CPDLC has also been a factor in navigation errors associated with a route change. Operators should be cognizant of this when designing operating procedures for the use of CPDLC.

6.4.1.6.7 Thoroughly brief all relief pilots on the newly effective route clearance prior to them assuming cockpit duties.

Note: We highly recommend that the relief pilot(s) also cross-check the FMS against the master document to ensure complete understanding of the new clearance.

6.4.1.7 You must ensure you have given an accurate ETA to ATC for your oceanic entry point. If a time estimate is found to be in error in excess of 2 minutes from that provided to ATC, a revised estimate must be provided to ATC.

6.4.1.8 You must also ensure you enter the ocean at your cleared/assigned FL for the crossing. The domestic ATC sector does not always automatically clear you to the oceanic clearance altitude; in this case, query ATC.

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6.4.2 Communications/Navigation/Surveillance System Checks.

6.4.2.1 You should have checked your high frequency (HF) radios prior to departure.

If you were unable to get a good check on the ground, check them prior to entering oceanic and remote continental airspace.

6.4.2.2 Accomplish a Selective Calling (SELCAL) check prior to oceanic and remote continental airspace entry and then again at each control area boundary. Check your SELCAL even when your CPDLC is working properly.

6.4.2.3 For commercial operators, your OpSpecs or MSpecs will prescribe the requirements for confirming your navigation accuracy, and assessing the performance of your LRNS, prior to entering oceanic airspace.

We recommend General Aviation (GA) operators perform similar navigation accuracy checks, as further described in paragraph D.2.5.1 of the sample oceanic checklist provided in Appendix D.

6.4.2.4 As discussed in paragraph 6.2.2.2 above, verify the RNP value set in your FMC matches the capability indicated in your flight plan.

6.4.2.5 If you plan on using satellite communications (SATCOM) data link systems, check them prior to oceanic airspace entry. ICAO Document 10037, GOLD, recommends you log on to CPDLC and/or ADS-C 10 to 25 minutes prior to the oceanic/FIR boundary.

6.4.2.6 Conduct altimetry checks prior to entering oceanic airspace and every hour thereafter. Your two primary altimeters should read within 200 feet of each other.

Note: We recommend you record these readings, along with their times, on your master document. This will aid you in determining the most accurate altimeter in the event of a subsequent altimetry problem.

6.4.3 Entering Oceanic and Remote Continental Airspace—First Steps.

6.4.3.1 Change your transponder code to 2000 in accordance with regional requirements. This requirement varies with the oceanic airspace. You should confirm these procedures, through applicable AIP or other regional documents during flight planning. In the North Atlantic, for example, the transponder code should be changed 30 minutes after entering oceanic airspace.

6.4.3.2 Adjust your airspeed to maintain your assigned Mach number, as applicable.

6.4.3.3 Once you have departed very high frequency (VHF) radio range, set your radios to air-to-air (generally 123.45) and guard (121.5) frequencies.

6.4.3.3.1 ATC and air defense authorities will generally attempt contact with aircraft on guard (121.5 or 243.0 megahertz (MHz)) before ordering an intercept.

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For this reason, all aircraft are “highly encouraged” to maintain a listening watch on guard.

6.4.3.3.2 The AIM, Chapter 5, Section 6, addresses interception procedures to include a reprint of the intercepting signals table published in ICAO Annex 2.

6.4.3.3.3 The International Air Transport Association (IATA) has developed widely adopted procedures for use in FIRs where poor communications and/or reduced quality of ATS pose a perceived flight hazard. See Appendix E, IATA In-Flight Broadcast Procedures, for IATA procedures for transponder use and radio broadcast in affected areas. The procedures involve maintaining a listening watch and broadcasting “in the blind.”

6.4.3.4 Institute an appropriate offset, based on the Strategic Lateral Offset Procedure (SLOP), unless not authorized. SLOP helps mitigate the heightened risk of collision due to highly accurate navigation systems, and it helps avoid wake turbulence.

6.4.3.4.1 SLOP procedures are published in the En Route (ENR) section of the U.S. AIP and ICAO Document 4444, section 16.5.

6.4.3.4.2 We recommend SLOP be part of your oceanic training program and standard procedures for oceanic flying. Many oceanic ATS providers have made SLOP a standard procedure in their airspace. You should check applicable State AIPs to determine where SLOP may not be authorized. The U.S. AIP, for example, authorizes only 1 NM offset increments.

6.4.3.5 Specify which FMS pages, or other monitorable elements of your navigation system, that individual flightcrew members are charged with monitoring during the oceanic portion of the flight (e.g., cross-track error or time/distance).

6.4.4 The Master Document: A Suggested Method for Managing It.

6.4.4.1 ICAO NAT Document 007 discusses the importance of a master document.

It requires that you use some form of master working document on the flight deck. You may base this document on the ATC flight plan, operational flight plan (navigation log), or other suitable document which lists sequentially the waypoints defining the route, the course and distance between each waypoint, and other information relevant to navigation along the cleared route.

6.4.4.2 Two minutes before reaching each oceanic waypoint, verify the next and subsequent (“next + 1”) waypoints. Using your currently effective route clearance, we recommend this verification include (1) a check of the expanded FMC coordinates for the next and subsequent waypoints and

(2) a check that the expected outbound magnetic course and distance to the next waypoint presented in the FMC agrees with that clearance.

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6.4.4.3 As you pass each waypoint, you can cross out the circled waypoint, waypoint number, or symbol to signify that the aircraft has passed the waypoint.

Note: Approaching a waypoint, some operators use a diagonal line to denote confirming a subsequent waypoint’s coordinates and the track and distance to it.

6.4.4.4 Verify the aircraft is progressing on the correct route by cross-checking the leg distance and magnetic course on the master document against the distance and magnetic course to the next point as displayed on the avionics.

6.4.4.5 As you make your position report over the waypoint, note your fuel remaining on the master document next to that waypoint. This is especially important if the cleared route and FL differ from your flight plan.

6.4.5 Position Reporting—General Requirements.

6.4.5.1 Communications over HF radio rely heavily on proper radio terminology and scripted reports. Use the published guidance found in en route publications or the AIM to make sure you deliver messages in the proper format.

1. You are expected to speak at a moderate speed using the internationally accepted phraseology.

2. Be certain you are communicating or logged on CPDLC with the ATC or communications facility appropriate to the oceanic and remote continental airspace in which you are operating or about to enter. More than one station may be using the same HF frequency at the same time. Only accept clearances from the ATS provider for the oceanic and remote continental airspace in which you are operating.

6.4.5.1.1 If you are operating within international airspace, make position reports either directly or by relay. If the ATS provider you are talking to is identified as a “Center,” (e.g., “Gander Center”) or a “Control” (e.g., “Tokyo Control”), you are talking directly to an air traffic controller. If the provider you are talking to is identified as a “Radio” (e.g., “Gander Radio”), you are talking to an aeronautical radio station, which is a relay facility that communicates between the ATC controlling facility and aircraft. An aeronautical radio station does not control air traffic—it relays the instructions of the ATC facility.

6.4.5.1.2 You must report departing your current FL. In certain regions, the NAT for example, you are also required to report reaching your assigned altitude.

You should consult the appropriate regional or State documents

(e.g., NAT Document 007, AIP, Airport/Facility Directory Supplement, etc.)

to confirm reporting requirements.

6.4.5.1.3 Make your position reports to the ATS provider for the airspace in which you are currently operating.

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6.4.5.1.4 In addition to reporting your position to your current ATS provider, in the case of boundary points, often you are expected to repeat your last position report to the FIR or control area (CTA) you are entering. Do so when so prescribed in the appropriate section of the ICAO Regional Supplementary Procedures (ICAO Document 7030), in the applicable AIP, or when requested by ATC.

6.4.5.1.5 If another aircraft relays your report, use the appropriate air-to-air frequency and not the emergency (guard) frequency.

6.4.5.1.6 If you operate in airspace approved for the use of data link, you may provide automatic position reporting via ADS-C logon. In this case, you should discontinue voice position reports.

6.4.5.2 When following a designated oceanic route, you must make position reports when passing each designated compulsory reporting point.

Note: The appropriate ATS authority may request reports over other points as well.

6.4.5.3 If you are not on a designated oceanic route, report your position at significant points listed in the flight plan. ATC expects reports as soon as possible after the first half hour of flight in oceanic and remote continental airspace and at hourly intervals thereafter. The appropriate ATS provider, however, may request additional reports at shorter intervals of time.

1. If your flight tracks predominantly east and west, ATS providers will generally request reports every 5° or 10° of longitude.

2. If your flight tracks predominantly north and south, ATS providers will generally request reports every 5° or 10° of latitude.

6.4.6 Position Reporting—Format.

6.4.6.1 See the AIM, Chapter 5, for general guidance on position report format.

You must provide information regarding your current fix and the next two fixes on your route of flight, in the following order:

1. Your complete aircraft call sign.

2. Your position and crossing time, reported in 4 digits UTC.

Note: You do not have to say “UTC” or “Zulu” when you report the time.

3. Your FL.

4. Your next fix and estimate over that fix in 4 digits UTC.

Note: If any reported ETA changes in excess of 2 minutes, you must provide an updated estimate to the ATS provider.

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5. Name of your subsequent fix.

6.4.6.2 When position is expressed in coordinates, the following pertains:

1. If your flight tracks predominantly east and west, ATS providers will generally expect latitude to be expressed in degrees and minutes, and longitude in whole degrees only.

2. If your flight tracks predominantly north and south, ATS providers will generally expect latitude to be expressed in whole degrees only, and longitude in degrees and minutes.

6.4.6.3 A 2010 change to ICAO Annex 3, Meteorological Services for International Air Navigation, cancelled the requirement to report wind and temperature data via voice. You should continue to report any turbulence or other significant meteorological conditions you encounter to ATC.

Note 1: Ensure the reporting of such meteorological observations references your geographical coordinates at the time of occurrence.

Note 2: ICAO NAT Document 007 has a form for reporting significant wake turbulence encounters. We encourage you to submit this form whenever you encounter significant wake turbulence while operating in NAT airspace, in order to support the monitoring efforts of the NAT airspace authorities.

6.4.7 Navigation Cross-Checking Procedures: Why They Are Important.

6.4.7.1 ICAO Document 7030, Regional Supplementary Procedures, includes language requiring the State of Registry or the State of the Operator to approve operator programs established to mitigate the occurrence of navigational errors due to equipment malfunction or operational error.

These operator programs must include in-flight operating drills, consisting of mandatory navigation cross-checking procedures, to identify navigation errors in sufficient time to prevent aircraft from inadvertent deviation from an ATC-cleared route.

6.4.7.2 Navigation cross-check procedures mitigate risk and promote situational awareness—an essential requirement for crews operating highly automated airplanes in increasingly crowded airspace. Such procedures help ensure aircraft operating under procedural ATC control are in fact maintaining the separation from other aircraft that ATC has planned and is expecting.

Cross-check procedures enable pilots to be certain they are where they think they are; this awareness becomes particularly critical during emergency situations.

6.4.7.3 While advances in navigation accuracy and communications capability generally enhance safety and reduce flightcrew and controller workloads, 6-18

these advancements have not eliminated human errors. Pilot deviations continue to occur and can be attributed to complacency, poor operational procedures, poor understanding of systems and processes, or simply human frailties such as cognitive or auditory failures.

Note: Numerous deviations in oceanic airspace have been caused by flightcrews failing to follow revised clearances. Transposed numbers, misunderstood clearances, or route amendments not properly verified or not passed on to relief crewmembers also contribute to navigation errors.

6.4.8 Navigation Cross-Checking—Acceptable Procedures.

6.4.8.1 In line with the rationale and requirements for navigation cross-checking procedures described in paragraph 6.4.7, the FAA believes cross-checking is synonymous with “making sure.” We consider the “sample oceanic checklists,” provided in Appendix D of this AC, to provide operators with not only a “to-do” list but also a means to make sure certain items, known to result in navigation errors if overlooked or done incorrectly, are performed in an organized, systematic manner.

6.4.8.2 The sample checklists (simple and expanded versions) provided in Appendix D are derived from ICAO NAT OPS Bulletin 2014-001, Sample Oceanic Checklists. We have added to the ICAO version in a few important ways. Most significantly, we have provided two acceptable methods for cross-checking aircraft position at a point approximately 10 minutes after oceanic waypoint passage. Up to now the only recommended method of cross-checking aircraft position in the oceanic airspace environment was manual plotting on a chart. However, a panel of aviation industry and FAA personnel completed an Operational Safety Assessment of methods for cross-checking oceanic flight navigation. The panel determined that an alternative to manual plotting, by which aircraft position could be checked through use of aircraft FMS-driven navigation displays and indications, would provide for an equivalent level of safety. See Appendix D, paragraph D.2.9.2.

6.4.8.3 The check of aircraft position at a point approximately 10 minutes following waypoint passage is designed to enable you to observe and correct a navigation error before safety of flight is jeopardized. If you made a subtle mistake either while en route to or crossing a waypoint, 10 minutes of travel should allow you to observe that mistake before significant problems result.

These cross-checks are a backup to an otherwise well-planned flight that is being executed through systematic and disciplined attention to effective procedures, such as those provided in this chapter and Appendix D.

The cross-checks are not designed to overcome poor planning, sloppy procedures or inadequate attention to detail. To reiterate: in-flight operating drills, to include cross-checking of navigation during oceanic and remote continental airspace operations, are mandatory under ICAO standards.

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6.4.8.4 The FAA recognizes that, for any number of reasons, operators may require or choose to use navigation cross-checking procedures different from those in the oceanic checklist provided in Appendix D. For those operators who require operational approval, whether to operate in oceanic and remote continental airspace in general, to operate in airspace where RNP is prescribed, or to operate within oceanic and remote Special Areas of Operation (SAO), such as North Atlantic High Level Airspace (NAT HLA), their choice of procedures will help establish the basis of that approval. Operational approval will be predicated upon use of either the cross-checking procedures described in the sample oceanic checklist (Appendix D) or via an alternative method that will achieve an equivalent level of safety. In order to determine equivalent levels of flight safety, an operator’s proposed alternative cross-checking procedures will be assessed, by the PI and the regional SAO specialist, against the following criteria:

1. Are they written, standardized, and required for use by the operator’s flightcrews?

2. Do they require use of a plotting or orientation chart, of adequate scale, for reference/situational awareness purposes?

3. Do they address all the major functions/action points

(e.g., independent route verification; at waypoint passage; after waypoint passage) outlined in the sample oceanic checklist?

4. Do they provide for confirming that the aircraft is flying toward, via the expected course/track line, the intended/expected waypoint contained in the flight’s currently effective route clearance?

5. Do they prescribe periodic cross-checking, for reasonableness, of the position data reported by all onboard long range navigation systems?

6. Do they require checking of aircraft position approximately 10 minutes after each oceanic waypoint prescribed in the currently effective route clearance?

7. Do they direct prompt and proper correction for any detected deviations from the currently effective route clearance?

8. Do they establish acceptable tolerances for track deviation, as well as course/heading/distance between waypoints, when compared between the flight plan and the navigation system?

9. Do they include ready reference to, and direct compliance with, accepted in-flight contingency procedures (refer to ICAO Document 4444)?

Note: Alternative methods proposed by certificated operators will also require review/approval by the Air Transportation Division (AFS-200), Flight Standards Service, at FAA headquarters (HQ).

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6.4.8.5 If an operator adopts new oceanic procedures, it is crucial this be done as part of a carefully orchestrated effort in close coordination with both your PI and the regional SAO specialist. Checklists need to be tailored to reflect operator-unique aspects, manuals need to be updated, and crews need to be trained. Failure to properly implement the change can lead to confusion, misunderstandings, and errors.

6.4.8.6 Diligent cross-checking of the FMS and master document against the currently effective route clearance remains the key to preventing inadvertent deviations from the cleared route.

1. The active leg is the most immediate indication of adherence to the currently effective route clearance. The active leg is formed by a “FROM” position and a “TO” waypoint, and features an associated course to fly between the points; this information should be cross-checked against the operational flight plan.

2. In addition to verifying the “TO” waypoint, the FAA also recommends the flightcrew verify autopilot steering mode

(e.g., LNAV/NAV, not Heading (HDG)).

3. When checking waypoints, ensure you look at the “expanded”

(i.e., degrees and minutes) coordinates. Some waypoint labels can be misleading.

6.4.8.7 While the procedures discussed above, and the items provided in the oceanic checklists in Appendix D, emphasize prevention of lateral errors, we want to emphasize that altitude deviations and longitudinal errors are no less significant. Steps to avoid those two types of errors in oceanic operations are discussed further in paragraph 6.1.2.

6.4.9 Relief Pilots—Preparing to Assume Duties. Increasingly, with long-range operations, relief pilots are part of the crew. In such cases, it is vital to brief the relief pilot on all current operational issues affecting the flight.

1. Many navigation errors have been traced back to inadequate handoff between pilots who first loaded the route into the navigation system and relief pilots who took over hours into the flight. You must fully brief the relief pilot on your currently effective route clearance.

2. We recommend the relief pilot verify the current cleared route prior to occupying the seat, if practical. Work from the FMS to the master document to lessen the risk of expectation bias (seeing what is expected) and maintain an attitude of “healthy suspicion.”

6.4.10 Exiting Oceanic and Remote Continental Airspace. Refer to the Coast-In step in the Sample Expanded Oceanic Checklist (Appendix D).

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