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 69–80

Appendix A A.2.66 Visual Meteorological Conditions (VMC). Meteorological conditions expressed in terms of visibility, distance from cloud, and ceiling, equal to or better than specified minima.

A.2.67 Waypoint. A predetermined geographical position used for route definition, progress reports, or points for transitioning and/or circumnavigating controlled and/or SUA, that is defined relative to a ground-based NAVAID or in terms of latitude/longitude coordinates. Waypoints are identified as either:

A.2.67.1 Fly-By Waypoint. A waypoint that requires turn anticipation to allow tangential interception of the next segment of a route or procedure.

A.2.67.2 Flyover Waypoint. A waypoint at which a turn is initiated in order to join the next segment of a route or procedure.

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Appendix B APPENDIX B. SPECIAL AREAS OF OPERATION AND OPSPECs/MSPECs/LOAs B.1 Special Areas of Operation (SAO). SAOs are geographic areas having unique characteristics that require the use of special equipment, procedures, and/or techniques to safely conduct flight operations. In SAOs, the air traffic control (ATC) system supports a reduction in separation standards. This reduction in separation standards requires improved levels of performance, utilizing more precise navigation systems and data link communications systems. The tables below identify those operations specifications (OpSpecs), management specifications (MSpecs), and letters of authorization (LOA) typically required for operations in the geographic areas considered SAOs, as well as for oceanic and remote continental airspace operations in general. Absence of the MSpec and/or LOA notation on the authorization line

(e.g., OpSpec B041) indicates that an MSpec and/or LOA is not required for those operators who would ordinarily be issued MSpecs or LOAs. Operators should consult with their regional SAO specialist when first considering flights in these areas.

B.2 SAO-Specific OpSpecs/MSpecs/LOAs.

Auth OpSpec/MSpec/LOA Title B037 OpSpec/MSpec Operations in Central East Pacific (CEP) Airspace B038 OpSpec/MSpec North Pacific (NOPAC) Operations B039 OpSpec/MSpec/LOA Operations in North Atlantic High Level Airspace (NAT HLA) B040 OpSpec/MSpec Operations in Areas of Magnetic Unreliability B041 OpSpec North Atlantic Operations (NAT/OPS) with Two Engine Airplanes Under Part 121 B050 OpSpec/MSpec Authorized Areas of En Route Operation, Limitations, and Provisions B055 OpSpec/MSpec North Polar Operations B059 OpSpec Canadian MNPS (C-MNPS) (B059 is only issued to part 135 operators) B450 OpSpec/MSpec/LOA Sensitive International Areas B.3 Oceanic and Remote General OpSpecs/MSpecs/LOAs.

Auth OpSpec/MSpec/LOA Title A010 OpSpec/MSpec Aviation Weather Information A014 OpSpec IFR En Route Operations in Class G Airspace A018 OpSpec Scheduled Helicopter Operations A056 OpSpec/MSpec/LOA Data Link Communications B-1

Appendix B Auth OpSpec/MSpec/LOA Title A153 OpSpec/MSpec/LOA Automatic Dependent Surveillance-Broadcast (ADS-B) Out Operations Outside of U.S.-Designated Airspace A317 OpSpec Acceptance of a Fatigue Risk Management Plan (FRMP) A354 OpSpec/MSpec/LOA Automatic Dependent Surveillance-Broadcast (ADS-B) In-Trail Procedure (ITP) A355 OpSpec/MSpec/LOA Automatic Dependent Surveillance-Broadcast (ADS-B) In Operations B030 OpSpec IFR Navigation Using GPS/WAAS RNAV Systems B031 OpSpec/MSpec Areas of En Route Operation B032 OpSpec/MSpec En Route Limitations and Provisions B034 OpSpec/MSpec/LOA IFR Class I Terminal and En Route Navigation Using RNAV Systems B035 OpSpec/MSpec/LOA Class I Navigation in the U.S. Class A Airspace using Area or Long-Range Navigation Systems B036 OpSpec/MSpec/LOA Oceanic and Remote Continental Airspace Navigation Using Multiple Long-Range Navigation Systems (M-LRNS) B043 OpSpec/LOA Special Fuel Reserves in International Operations B044 OpSpec Planned Redispatch or Rerelease En Route B045 OpSpec/MSpec/LOA Extended Overwater Operations Using a Single Long-Range Communications System (SLRCS) B046 OpSpec/MSpec/LOA Operations in Reduced Vertical Separation Minimum (RVSM) Airspace B054 OpSpec/MSpec/LOA Oceanic and Remote Airspace Navigation Using a Single Long-Range Navigation System B342 OpSpec Extended Operations (ETOPS) with Two-Engine Airplanes, Under Parts 121 or 135 B343 OpSpec Fuel Reserves for Flag and Supplemental Operations B344 OpSpec Extended Operations in Passenger-Carrying Airplanes with More Than Two Engines, Under Parts 121 or 135 C055 OpSpec/MSpec Alternate Airport IFR Weather Minimums H104 OpSpec/LOA Helicopter En Route Descent Areas (HEDA) B-2

Appendix C APPENDIX C. UNUSUAL WEATHER ACTIVITY C.1 Volcanic Ash.

C.1.1 In 2010, a small volcano in Iceland erupted, spewing volcanic ash into the atmosphere.

Eyjafjallajökull’s eruption stranded 8 million travelers and resulted in the largest airspace shutdown since World War II. As a result, in 2012 the International Civil Aviation Organization (ICAO) produced the first edition of ICAO Document 9974, Flight Safety and Volcanic Ash, which provides guidance for aircraft operators when volcanic ash contamination may be a hazard for flight operations. Whenever your flight planned route approaches the vicinity of a volcanic ash cloud, you should understand the potentially catastrophic effects ingesting volcanic ash could have on your aircraft engines. Currently, nine Volcanic Ash Advisory Centers (VAAC) offer worldwide coverage of volcanic activity and provide valuable information to assist your trip planning efforts.

Figure C-1. ICAO Volcanic Ash Advisory Centers

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Appendix C C.1.2 Volcanic eruptions emit various gases along with magma, including sulfur dioxide (SO2) and hydrogen sulfide (H2S). When SO2 gas combines with water in the atmosphere, a sulfate aerosol primarily composed of dilute sulfuric acid is formed. Flying through sulfuric acid aerosols has caused crazing of acrylic windows, fading of exterior paint, and accumulation of sulfate deposits in engines. SO2 gas is colorless, but under certain conditions of reflection and refraction of sunlight, a sulfuric acid aerosol may be a visible atmospheric feature, such as a layer of haze of variable color (brownish, yellowish, bluish, or whitish). Ash particles likely will be present in aerosol haze but possibly in minor or trace amounts.

C.1.3 Volcanoes are the only sources of large quantities of sulfur gases at cruise altitudes, and both types of sulfur gas have a noticeable smell. SO2 is identifiable as the sharp, acrid odor of a freshly struck match. H2S, also known as sewer gas, has the odor of rotten eggs.

“Electrical smoke and fire” and SO2 are two odors described as somewhat similar. Sulfur gases may be detectable only for a short period of time because of “olfactory fatigue” (temporary loss of the ability to smell a particular odor). Inhalation of SO2, even at low concentrations (<5 ppm), can cause respiratory tract irritation, especially in people with asthma and chronic obstructive pulmonary disease.

C.1.4 If you smell sulfur gases in the cockpit, this may indicate volcanic activity that has not yet been detected or reported and/or your possible entry into an ash-bearing cloud. After determining there are no secondary indications that would result from and indicate an electrical fire, you should establish whether the sulfur odor is transient or not.

C.1.5 You can best achieve this by donning your oxygen mask(s) and breathing 100 percent oxygen for the period of time that results in a complete change of air within the cockpit and also allows you to regain your sense of smell. After the appropriate time period, remove your oxygen mask(s) and determine if the odor is still present. If you confirm the continued presence of sulfur gas, you should inform the controlling Air Traffic Service (ATS) unit and dispatch center as soon as practicable to request information about any relevant volcanic activity and the whereabouts of possible volcanic clouds. You do not have the means to determine directly whether or not the cloud is hazardous; therefore, you should seek to exit the cloud.

C.1.6 You might see other indications of volcanic ash such as fine dust in the aircraft, St. Elmo’s fire visible around your windshield, and/or a visible glow in the intake of your engines. Your airspeed indications may also become unreliable as the ash contaminates your pitot/static system. Chapter 7 of the Aeronautical Information Manual (AIM) discusses Pilot Weather Reports (PIREP) related to volcanic ash activity and recommends you complete the Volcanic Activity Reporting Form, found in Appendix 2 of the AIM.You should avoid flying in the vicinity of known volcanic ash. Attempting to overfly an ash plume is also potentially perilous, as an emergency descent could place the aircraft into the plume.”

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Appendix C C.2 Space Weather.

C.2.1 The effects of space weather on aviation have generated an increasing amount of interest in recent years. Space weather most commonly impacts radio communications between your aircraft and ground stations. Space weather may also impact navigation signals from space-based and ground-based transmitters as well as onboard avionics components.

Exposure to increased radiation levels during solar events has not been a noticeable issue, but it is a factor that you can plan for in order to protect your frequently flying crewmembers and passengers.

C.2.2 The magnetic field around the Earth converges at the North and South Poles, allowing charged particles to access lower levels of the Earth’s atmosphere. These lower levels are the same levels used to fly international flights around the world. The aviation community has shown increasing interest in this phenomenon at the poles as the expansion of polar routes has seen more and more flights susceptible to space weather.

C.2.3 The solar cycle is an approximately 11-year period that is characterized by solar activity that departs from the sun and has impacts on whatever celestial bodies are in the path of this space weather. The current cycle, Cycle 24, peaked in early 2014 and should bottom out around 2019–2020. The three effects of this weather are known as radio blackouts, geomagnetic storms, and solar radiation storms. These storms can have varying degrees of short- and long-term impact on ground-based navigation signals, aircraft and aircrew in flight, space-based transmitters, spacecraft, and space crew.

The Space Weather Prediction Center tracks these storms and issues space weather watches, warnings, and alerts to inform the public of potential impacts.

Figure C-2. Example of a National Oceanic and Atmospheric Administration Scales Activity Report

C.2.4 Space weather alerts can be subscribed to through the Space Weather Prediction Center Product Subscription Service and the following link:

http://www.swpc.noaa.gov/communities/space-weather-enthusiasts.

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Appendix D APPENDIX D. SAMPLE OCEANIC CHECKLIST D.1 Sample Oceanic Checklist. This sample checklist is provided for your reference. If you do not have an oceanic checklist, we encourage you to use this sample and tailor it to your specific needs and approvals. This checklist focuses on an orderly flow and ways to reduce oceanic errors. You should also review the expanded checklist at paragraph D.2. You should use the International Civil Aviation Organization’s (ICAO) Oceanic Errors Safety Bulletin (OESB) with this checklist. An oceanic checklist should be part of your Safety Management System (SMS). Other sample oceanic checklists are available through the ICAO North Atlantic (NAT) Ops Bulletins, found at www.icao.int.

D.1.1 Flight Planning.

D.1.1.1 Communications, navigation, and surveillance flight plan codes and planning documents.

D.1.1.2 Oceanic documents.

D.1.1.3 Plotting/orientation chart—plot route coast out to coast in.

D.1.1.4 Equal time points (ETP)—plot.

D.1.1.5 Track message (current copy available for all crossings).

Note: Note nearest tracks on plotting/orientation chart.

D.1.1.6 Weather analysis—note en route temperature and turbulence forecasts as well as ETP airport weather.

D.1.1.7 Review suitable navigation aids (NAVAID) for accuracy check prior to coast out.

D.1.2 Preflight.

D.1.2.1 Master clock for all estimated times of arrival (ETA)/actual times of arrival (ATA).

D.1.2.2 Maintenance log—check for any communications, navigation, and surveillance or Reduced Vertical Separation Minimum (RVSM) issues.

D.1.2.3 RVSM.

D.1.2.4 Altimeter checks (tolerance).

D.1.2.5 Wind shear or turbulence forecast.

D.1.2.6 Flight plan (check routing, fuel load, times, groundspeeds).

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Appendix D D.1.2.7 Dual long-range navigation system (LRNS) for oceanic and remote continental airspace operations.

D.1.2.8 High frequency (HF) check (including Selective Calling (SELCAL)).

D.1.2.9 Confirm present position coordinates (best source).

D.1.2.10 Master document symbols (, , \, X).

D.1.2.11 LRNS programming:

1. Check navigation database currency and software version.

2. Independently verify flight management system (FMS) programming.

3. Check expanded coordinates of oceanic waypoints.

4. Check course and distance (± 2° and ±2 nautical miles (NM)).

5. Upload winds, if applicable.

D.1.2.12 Groundspeed check.

D.1.3 Taxi and Prior to Takeoff.

D.1.3.1 Groundspeed check.

D.1.3.2 Present position check.

D.1.4 Climb Out.

D.1.4.1 Transition altitude—set altimeters to 29.92 inches (1013.2 hectopascals).

D.1.4.2 Manually compute ETAs as duties permit.

D.1.5 Prior to Oceanic Entry.

D.1.5.1 Navigation accuracy check—record results on master document.

D.1.5.2 HF check, if not done during preflight.

D.1.5.3 Confirm satellite communication (SATCOM) data link is operational, if equipped.

D.1.5.4 Log on to Controller-Pilot Data Link Communication (CPDLC) and Automatic Dependent Surveillance-Contract (ADS-C) 10 to 25 minutes prior, if equipped.

D.1.5.5 Verify your Required Navigation Performance (RNP) value.

D.1.5.6 Obtain oceanic clearance from appropriate clearance delivery and verify/cross-check air traffic control (ATC) route clearance is properly programmed into the LRNS.

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Appendix D

1. Confirm assigned oceanic flight level (FL) and request climb or descent to be at your assigned FL prior to oceanic airspace boundary.

2. Confirm FL, Mach, and route for crossing.

3. Advise ATC when able higher.

D.1.5.7 Reclearance—update LRNS, master document, and plotting/orientation chart.

Note: Check course and distance for new route.

D.1.5.8 Check altimeters—record readings on master document.

D.1.5.9 Compass heading check (inertial navigation system (INS))—record.

D.1.6 After Oceanic Entry.

D.1.6.1 Squawk 2000—30 minutes after entry, if applicable.

D.1.6.2 Maintain assigned Mach.

D.1.6.3 Maintain assigned FL.

D.1.6.4 Very high frequency (VHF) radios—set to air-to-air and guard frequency.

D.1.6.5 Strategic Lateral Offset Procedure (SLOP)—Depending on standard operating procedures (SOP), fly cleared route or up to 2 NM to the right of ATC-cleared track. Confirm procedures in the State Aeronautical Information Publication (AIP).

D.1.6.6 Altimeter checks—hourly.

D.1.7 Approaching Waypoints.

D.1.7.1 Confirm coordinates of subsequent waypoints.

Note: Verify that the active FMS waypoint, as well as the next and subsequent (“next plus 1”) waypoints, match your currently effective route clearance. Confirm that the expanded (i.e., full latitude and longitude coordinates) of the next and subsequent waypoints, as well as the course/heading and distance to the waypoints, agree with your currently effective route clearance.

D.1.7.2 Confirm lateral navigation (LNAV)/navigation (NAV) is engaged.

D.1.8 Overhead Waypoints.

D.1.8.1 Confirm aircraft transitions to next waypoint.

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Appendix D Note: Check magnetic heading and distance against master document.

D.1.8.2 Confirm time to next waypoint.

Note: ETA changes in excess of 2 minutes require ATC notification.

D.1.8.3 Make position report.

Note: Record fuel remaining and current time on your master document.

D.1.9 Ten Minutes after Waypoint Passage. Cross-check navigational performance and course compliance via one of the following methods:

D.1.9.1 Plotting method (see paragraph D.2.9).

D.1.9.2 Navigation display method (see paragraph D.2.9).

D.1.9.3 Alternative method accepted by the FAA (see paragraph 6.4.8).

D.1.10 Midway Between Waypoints.

D.1.10.1 Cross-check winds between master document, LRNS, and winds aloft charts.

D.1.10.2 Confirm time to next waypoint.

D.1.11 Coast In.

D.1.11.1 Remove strategic lateral offset prior to oceanic exit point.

D.1.11.2 Confirm routing beyond oceanic airspace.

D.1.11.3 Compare LRNS to ground-based NAVAID.

D.1.12 Descent. Transition level—set altimeters to barometric pressure for local altimeter setting (QNH).

D.1.13 Destination/Block-In.

D.1.13.1 Navigation accuracy check.

D.1.13.2 RVSM write-ups.

D.2 Sample Expanded Oceanic Checklist. This sample expanded checklist is provided for your reference. If you do not have an expanded oceanic checklist, we encourage you to use this sample and tailor it to your specific needs and approvals. This checklist focuses on an orderly flow and ways to reduce oceanic errors. You should use the ICAO OESB together with this checklist. An oceanic checklist should be part of your Safety Management System (SMS).

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