High Latitude Operations
If you fly over the poles under 14 CFR 135, you need to understand everything written below about high latitude operations. It could very well be that you can't legally do what your airplane is physically capable of doing.
Flying over the poles under 14 CFR 91? You still need to understand this stuff, but you might not be prevented from doing something stupid. Me? I would make sure we had all our ducks in line first. What follows will help you do just that.
- Location — What defines a high latitude? It is more than just the poles.
- Documentation / Certification — Operations Specifications for 14 CFR 135.
- Equipment — Equipment and MEL Requirements.
- Training — Training Requirements.
- Communications Issues — VHF, HF, and SATCOM.
- Navigation Issues — Problems with magnetic variation and the need to use True.
- Temperature Issues — Temperatures at altitude, on the surface, and of your fuel.
- Polar Radiation Issues — Greater exposure at the poles.
- Alternate Airports — Not only do you need alternates, you need an evacuation plan.
[Advisory Circular 120-42B, ¶601.]
- The North Polar Area is defined as the entire area north of latitude 78 degrees North.
- The South Polar Area is defined as the entire area south of latitude 60 degrees South.
[Advisory Circular 91-70A, ¶ 3-6.w.] Navigation in Areas of Magnetic Unreliability (AMU). The FAA designates Canada's NCA and Arctic Control Area (ACA) as AMUs. Although Canadian publications sometimes refer to it as the area of compass unreliability, they are the same. The magnetic North Pole is at approximately 75°N 100°W and is slowly moving as it circles the true pole every 960 years. This is why we see current navigation charts occasionally changing an instrument landing system (ILS) course by 1°.
- Magnetic North Pole. When you approach the magnetic North Pole, horizontal magnetic influences decrease and vertical magnetic influences increase to a point where the compass is no longer reliable (the magnetic pole is below the aircraft). It is common to see the compass drifting aimlessly or tilting in its case due to the vertical component even when hundreds of miles from the magnetic North Pole. The better the magnetic compass, the closer to the magnetic pole it will operate. Within about 250 miles of the magnetic pole, all aircraft magnetic compasses will be useless. As a result, some VORs, runways, and radar vectors in Canada's NCA and ACA are oriented to true north.
- AMU. When operating in the AMU, move the HDG REF switch to TRUE when the Canada HI 4 chart defines the course with a °T. Add two additional items to the master flight plan checklist: TRUE HDG adjacent to the first true heading leg and MAG HDG at the end of the AMU. This will serve as a reminder to return to a normal heading reference. The primary reason for selecting TRUE HDG in the NCA and ACA is to provide a more realistic navigation display (ND) heading presentation, thus avoiding rapidly changing heading indications. This will help with radar vectors in TRUE and comply with Canadian Air Regulations.
The worst magnetic compass performance is probably in the center of the Northern Control Area, home to the magnetic North Pole. This position creates a notch in the circle of magnetic unreliability, often called a "key hole." Charts should be checked for the presence of a "T" denoting the use of True Heading instead of Magnetic. Some aircraft automatically switch to True based on airway designation or latitude. The G450, for example, automatically switches above N73° or S60° latitude. More about this: G450 FMS: True/Magnetic Selection.
Figure: Southern, Northern, and Arctic Control Areas, (Transport Canada Aeronautical Information Manual, Figure 2.3)
- Controlled airspace within the High Level Airspace is divided into three separate areas. They are the Southern Control Area (SCA), the Northern Control Area (NCA) and the Arctic Control Area (ACA).
- Pilots are reminded that both the NCA and the ACA are within the Northern Domestic Airspace; therefore, compass indications may be erratic, and true tracks are used in determining the flight level at which to fly. In addition, the airspace from FL330 to FL410 within the lateral dimensions of the NCA, the ACA and the northern part of the SCA has been designated CMNPS airspace.
What we used to call "polar ops" is now "high latitude operations." The definition depends on your source of information but can be summarized as follows:
- The northern and southern poles.
- The Canadian Northern Domestic Area (NDA). The NDA includes the Northern Control Area (NCA), the Arctic Control Area (ACA) and the Area of Magnetic Unreliability (AMU). The NDA, NCA and ACA are depicted on Canadian HI en route charts and encompass the northernmost Canadian airspace.
Documentation / Certification
[14 CFR 135, §135.98 Operations in the North Polar Area.] After February 15, 2008, no certificate holder may operate an aircraft in the region north of 78° N latitude (“North Polar Area”), other than intrastate operations wholly within the state of Alaska, unless authorized by the FAA. The certificate holder's operation specifications must include the following:
- The designation of airports that may be used for en-route diversions and the requirements the airports must meet at the time of diversion.
- Except for all-cargo operations, a recovery plan for passengers at designated diversion airports.
- A fuel-freeze strategy and procedures for monitoring fuel freezing for operations in the North Polar Area.
- A plan to ensure communication capability for operations in the North Polar Area.
- An MEL for operations in the North Polar Area.
- A training plan for operations in the North Polar Area.
- A plan for mitigating crew exposure to radiation during solar flare activity.
- A plan for providing at least two cold weather anti-exposure suits in the aircraft, to protect crewmembers during outside activity at a diversion airport with extreme climatic conditions. The FAA may relieve the certificate holder from this requirement if the season of the year makes the equipment unnecessary.
[FAA Order 8900, Volume 4, Chapter 1, §5, ¶4-102.E.] All approvals for operations into AMUs are granted by issuing OpSpec paragraph B040, Operations in Areas of Magnetic Unreliability, and by adding that area of en route operation to paragraph B050 of the standard OpSpecs. A checklist for operations in AMUs is available in the guidance subsystem in association with OpSpec paragraph B040.
Crews operating under 14 CFR 135 require operations specification approval (B040 and B050).
Crews operating under 14 CFR 91 should consider the many challenges involved and the potential safety risks illustrated below.
[Advisory Circular 135-42, Appendix 3, ¶3.f.] Certificate holders must have at least two cold weather anti-exposure suit(s) for the crewmembers on the airplane if outside coordination by a crewmember at a diversion airport with extreme climatic conditions is determined to be necessary. The certificate holder may be relieved of this requirement based on seasonal temperatures that would render the use of such suits unnecessary. This determination must be made with concurrence of the CHDO.
This isn't much of a list; you would be wise to consider adding the requirements of Advisory Circular 120-42B, which do not restrict 14 CFR 135 and 91, but offer sound operating practices.
[Advisory Circular 120-42B, ¶603.b.(5)]
- Fuel quantity indicating system (FQIS), including the fuel tank temperature indicating system;
- APU (when the APU is necessary for an airplane to comply with ETOPS requirements), including electrical and pneumatic supply to its designed capability,
- Autothrottle system;
- Communication systems relied on by the flight crewmember to satisfy the requirement for communication capability; and
- Except for all-cargo operations, an expanded medical kit to include automated external defibrillators (AED).
[FAA Order 8900, Volume 4, Chapter 1, §5, ¶4-102.C.]
- Special navigation equipment, techniques, and/or procedures are critical to operate safely in polar areas, including the two AMUs. Operations based solely on magnetic references within AMUs are unsafe, unacceptable, and shall not be approved. Operations within these areas can only be conducted safely if the primary heading reference is derived from sources other than magnetic.
- All INS/IRS/IRU are capable of calculating true North independently from other aircraft systems. INS/IRS/ IRU can be approved and safely used for operations in AMUs and polar areas provided the following conditions are met:
- The INS is certified as airworthy for the highest latitude authorized for these operations.
- Ground alignment of the INS/IRS/IRU is restricted to those airports where satisfactory alignment has been demonstrated or otherwise approved.
- The operator's training programs and crew procedures provide acceptable techniques and methods for the following:
- Approaches and departures using appropriate heading references other than magnetic
- The use of ground-based NAVAIDs, which are oriented to appropriate directional references other than magnetic
[Advisory Circular 135-42, Appendix 3, ¶3.c.] Before receiving approval to conduct polar operations, a certificate holder must review their MEL for such operations and should amend their MEL. The following systems and equipment should be addressed in the MEL based on specific needs applicable to this operation.
(1) Fuel Quantity Indicating System (to include a fuel tank temperature indicating system).
(2) Communication system(s) needed for effective communications by the flight crewmember while in flight.
(3) Expanded medical kit.
[Advisory Circular 135-42, Appendix 3, ¶3.e.] Before conducting polar operations, certificate holders must ensure that flight crewmembers are trained on any applicable passenger recovery plan used in this operation. Certificate holders should also ensure that flight crewmembers are trained on the following items, which should be included in a certificate holder's approved training programs:
(1) Atmospheric pressure at Field Elevation/Barometric pressure for Local Altimeter Setting and meter/feet conversion issues (flight crewmember training).
(2) Training requirements for fuel freeze (maintenance and flight crewmember training).
(3) General polar-specific training on weather patterns and aircraft system limitations (flight crewmember training).
(4) Proper use of the cold weather anti-exposure suit, if required (flight crewmember training).
(5) Radiation exposure (see AC 120-61A, In-Flight Radiation Exposure).
[FAA Order 8900, Volume 4, Chapter 1, §5, ¶4-103.D.] The following must be in the approved training programs:
- Training on Barometric pressure for Standard Altimeter Setting (QNE)/ Barometric pressure for Local Altimeter Setting (QNH) and meter/feet issues is required for flight crew and dispatcher training.
- Training on fuel freeze (included in maintenance, dispatch, and flight crew training (special curriculum segments.))
- General area and route-specific training on weather patterns and aircraft system limitations.
- Training on special considerations, such as diversion decision-making into austere airport environments to include aircraft performance, crash, fire, and rescue availability, and passenger support.
- Flight crew training in the use of the cold weather anti-exposure suit.
Figure: Arctic Radio VHF, (Jeppesen Airway Manual AP(HI))
There is some VHF radio coverage, denoted on en route charts.
Figure: Arctic HF / CPDLC Example, (Jeppesen Airway Manual AP(HI))
HF Frequencies and CPDLC addresses also appear on en route charts.
[FAA Order 8900, Volume 4, Chapter 1, §5, ¶4-103.B.(2)] High frequency (HF) voice has been considered the primary communications medium in the North Polar Area. However, other mediums may be used as a supplemental means in accordance with the applicable policy. For example, although HF voice remains primary for communications with Anchorage Center, in areas where there is satellite coverage, satellite communication (SATCOM) voice may be used as a back-up to communicate with ARINC Radio and in non-routine situations to establish direct pilot-controller voice communications.
I am told the HF quality is generally good, though signals may be impacted by solar activity. You may need to use either AM, USB or LSB to achieve the best clarity.
SATCOM / CPDLC
Figure: INMARSAT Line of Sight, (Eddie's Notes)
[FAA Order 8900, Volume 4, Chapter 1, §5, ¶4-103.B.(3)] In areas of satellite coverage, Controller-Pilot Data Link Communications (CPDLC) may be used for ATC communications, provided the ATS unit has an approved capability. In addition, provided the capability is approved, HF datalink may also be used to fulfill communications requirements with ATS units having the capability and with airline dispatch. Inspectors must ensure the operators meet the regulatory (14 CFR part 1) and policy requirements for long-range communication systems (LRCS). HF voice capability is always required.
[FAA Order 8900, Volume 4, Chapter 1, §5, ¶4-103.B.(4)] It is recognized that SATCOM may not be available for short periods during flight over the North Pole, particularly when operating on some designated polar routes. Communication capability with HF radios may also be affected during periods of solar flare activity. For each dispatched polar flight, the operator must take into consideration the predicted solar flare activity and its effect on communication capability.
[G450 Aircraft Operating Manual, §2B-21-40, ¶1.D.]
- All PLANEVIEW CMF transmissions, whether VHF or satellite, require line of sight to a VHF ground station or Inmarsat satellite, respectively.
- Transmitting by way of satellite while on the ground is generally reliable. Although, line of sight issues may still arise due to surrounding terrain and man made structures because the Inmarsat satellites are in an equatorial geostationary orbit. In flight, the curvature of the Earth is a concern only at latitudes greater than 70° North or South. Except at these high latitudes, satellite coverage while in flight is seamless.
Because INMARSAT satellites are in geostationary orbits over the equator, the curvature of the earth limits their use at the poles. It is said that SATCOM is available for voice and datalink up to 82°N.
As in other remote areas, do not enter holding for lack of further clearance or radio contact at the FIR. Continue on your cleared route and altitude while trying pass a position report through the appropriate agency or a relay by another aircraft that you might raise on guard or on the air-to-air frequency 123.45 MHz. In the event of a total loss of communications, fly your flight plan.
More about: Lost Communications.
Magnetic Variation and Convergence of the Meridians
Figure: Magnetic Variation Convergence Example, (Eddie's notes)
[FAA Order 8900, Volume 4, Chapter 1, §5, ¶4-102.]
- Conventional magnetic compasses sense magnetic direction by detecting the horizontal component of the earth's magnetic field. Since this horizontal component vanishes near the magnetic poles, magnetic compasses are highly unreliable and unusable in an area approximately 1,000 NM from each magnetic pole. Within these areas, air navigation tasks are further complicated by very rapid changes in magnetic variation over small distances. For example, when flying between the magnetic North Pole and the true North Pole, a heading of true North results in a magnetic heading of South (a magnetic variation of 180 degrees).
- Since these two major AMUs also occur near the earth's geographic poles, the convergence of the meridians also presents additional directional complications. When flying "great circle" courses at latitudes greater than 67 degrees, convergence of the meridians can create rapid changes in true headings and true courses with small changes in aircraft position. As a result, relatively small errors in determining the aircraft's actual position can produce very large errors in determining the proper heading to fly and maintain the assigned flight path. When even small errors occur, very large navigation errors can develop over extremely short distances. An extreme example of this phenomenon occurs at the earth's geographic North Pole. Flight in any direction from the exact pole is initially due South (that is, the direction to Russia or the United States is South).
The example chart illustrates the rapid change in magnetic heading over a relatively short distance.
Figure: True vs. Magnetic Example, (Jeppesen Airway Manual AP(HI))
Navigating near the poles presents several issues not found anywhere else in the world. Because of these issues, the only acceptable method of navigating through the NCA and high latitude region is through the use of long-range navigation systems using inertial and GPS based FMS systems referenced to True North only.
Other methods of navigation in the NCA are impractical or unreliable because of the inherent limitations of magnetic compasses near the magnetic and geographic North Poles, and because of the geometric problem caused by meridian convergence.
Some aircraft make the switch automatically by reference to latitude or airway, while for other the switch must be made manually. See: G-450 FMS True/Magnetic Selection for more details.
Figure: GPS Satellite Line of Sight, (Eddie's notes)
Each GPS satellite traces a track over the earth from 55° North to 55° South every twelve hours. At their maximum latitudes they are actually "looking down" on the poles:
Of course you have no guarantee you will have at least one satellite that high in its orbit. In order to have line of sight on the pole, a satellite would have to be at least 39° latitude:
I've not found anything in writing that tells you there will always be at least four satellites above 39° North and 39° South, but it appears so. You should have a good GPS position at either pole.
More about this: GPS.
Tropopause Height and ISA
Figure: Tropopause Height, (Geerts and Linacre.)
- The height of the tropopause depends on the location, notably the latitude, as shown in the figure on the right (which shows annual mean conditions). It also depends on the season.
- At latitudes above 60°, the tropopause is less than 9-10 km above sea level; the lowest is less than 8 km high, above Antarctica and above Siberia and northern Canada in winter. The highest average tropopause is over the oceanic warm pool of the western equatorial Pacific, about 17.5 km high, and over Southeast Asia, during the summer monsoon, the tropopause occasionally peaks above 18 km. In other words, cold conditions lead to a lower tropopause, obviously because of less convection.
- Deep convection (thunderstorms) in the Intertropical Convergence Zone, or over mid-latitude continents in summer, continuously push the tropopause upwards and as such deepen the troposphere.
- On the other hand, colder regions have a lower tropopause, obviously because convective overturning is limited there, due to the negative radiation balance at the surface. In fact, convection is very rare in polar regions; most of the tropospheric mixing at middle and high latitudes is forced by frontal systems in which uplift is forced rather than spontaneous (convective). This explains the paradox that tropopause temperatures are lowest where the surface temperatures are highest.
The tropopause at the poles is lower than at the equator; that means the altitudes where most polar-capable aircraft cruise is warmer. Knowing this, altitude selection may not be straight forward.
More about this: Properties of the Atmosphere.
Figure: North Pole January Mean Temperatures, (Wikimedia Commons)
If a descent into lower altitudes is required, fuel freezing and other aircraft systems limitations can become issues. If an emergency landing is required, surface temperatures can be life threatening. See: Fuel Freezing, and Minimum Equipment List.
[Advisory Circular 135-42, Appendix 3, ¶3.c.] Fuel Freeze Strategy and Monitoring Requirements for Polar Operations. Certificate holders must develop a fuel freeze strategy and procedures for monitoring fuel freezing for operations in the North Polar Area. A fuel freeze analysis program in lieu of using the standard minimum fuel freeze temperatures for specific types of fuel may be used. In such cases, the certificate holder's fuel freeze analysis and monitoring program for the airplane fuel load must be acceptable to the FAA Administrator. The certificate holder should have procedures for determining the fuel freeze temperature of the actual fuel load on board the airplane. These procedures relative to determining the fuel freeze temperature and monitoring the actual temperature of the fuel on board should require appropriate levels of coordination between maintenance and the flight crewmember.
Should fuel temperatures approach the aircraft’s freezing limit you should consider:
- Climbing or descending into a level of warmer air,
- Altering the route into a region of warmer air, and/or
- Increasing cruise airspeed (Fuel temperatures should increase approximately one degree for every .02 increase in Mach speed)
Your flight planning vendor should provide a temperature chart to help you plan for these contingencies. Remember, any changes in flight level, speed or route must be coordinated with ATC.
For more on weather at high latitudes, see: Arctic Weather.
Figure: Solar Flare, (Wikimedia Commons)
[Advisory Circular 120-61A, ¶6.] Radiation received on a lower-latitude flight will be lower because of the greater amount of radiation shielding provided by the earth's magnetic field. This shielding is maximum near the equator and gradually decreases to zero as one goes north or south. Radiation levels over the polar regions are about twice those over the equator at the same altitudes.
- Space radiation on the ground is very low, but increases significantly with altitude. At 30,000 to 40,000 feet, the typical altitude of a jetliner, exposure on a typical flight is still considered safe – less than a chest X-ray.
- Exposure is considerably higher, however, over the Earth's poles, where the planet's magnetic field no longer provides any shielding. And with a thousand-fold rise in commercial airline flights over the North Pole in the last 10 years, exposure to radiation has become a serious concern.
- A study by Mertens of polar flights during a solar storm in 2003 showed that passengers received about 12 percent of the annual radiation limit recommended by the International Committee on Radiological Protection. The exposures were greater than on typical flights at lower latitudes, and confirmed concerns about commercial flights using polar routes.
- People who work on commercial airline flights are technically listed as "radiation workers" by the federal government – a classification that includes nuclear plant workers and X-ray technicians. But unlike some others in that category, flight crews do not quantify the radiation they are exposed to.
Flights in the Polar Region at typical business jet operating altitudes are well above the tropopause where much of the atmospheric protection from solar storms is lost, increasing crew and passenger exposure to solar radiation.
For example, one New York-Tokyo flight during a solar storm could expose the passengers and crew to the normal annual exposure (1mSv) of someone who remained on the surface. If an S4 solar storm is active or predicted, polar operations are generally considered not suitable at any altitude, while operations at FL310 or below are considered acceptable in S3 storm conditions.
Some flight plan vendors will include predicted solar activity for flights through the high latitude airspace. Additionally, Space Weather Now from the NOAA and spaceweather.com are useful when planning a polar flight.
Figure: Arctic Alternates, (Eddie's notes)
[Advisory Circular 135-42, Appendix 3, ¶3.a.] Before each flight, certificate holders must designate alternate airports that can be used in case an en route diversion is necessary. The airplane should have a reasonable assurance that the weather during periods when the certificate holder would need the services of the airport are within the operating limits of the airplane. The airplane should be able to make a safe landing and maneuver off the runway at the diversion airport. In addition, those airports identified for use during an en route diversion should be capable of protecting the safety of all personnel by allowing:
(1) Safe offload of passengers and crewmember during possible adverse weather conditions;
(2) Providing for the physiological needs of the passengers and crewmember until a safe evacuation is completed; and
(3) Safe extraction of passengers and crewmember as soon as possible (execution and completion of the recovery should be within 12 to 48 hours following landing).
[FAA Order 8900, Volume 4, Chapter 1, §5, ¶4-103.E.] Operators are expected to define a sufficient set of polar diversion alternate airports, such that one or more can be reasonably expected to be suitable and available in varying weather conditions (AC 120-42A, Extended Range Operation With Two-Engine Airplanes (ETOPS), provides additional guidance for two-engine airplanes).
[FAA Order 8900, Volume 4, Chapter 1, §5, ¶4-103.G.] A recovery plan is required that will be initiated in the event of an unplanned diversion. The recovery plan should address the care and safety of passengers and flight crew at the diversion airport and include the plan of operation to extract the passengers and flight crew from that airport.
The requirements for the passenger recovery plan are quite extensive and must be detailed for each airport listed as a possible alternate airport.
More on this: Advisory Circular 135-42, Appendix 3, ¶3.b.
There aren't many airports with paved runways in the Arctic, and many of those do not have regular airline service or customs. If you are flying under 14 CFR 135 your Operations Specification approval will require a list of alternates and a plan for getting passengers from the alternates within 48 hours.
14 CFR 135, Title 14: Aeronautics and Space, Operating Requirements: Commuter and On Demand Operations and Rules Governing Persons on Board Such Aircraft, Federal Aviation Administration, Department of Transportation
Advisory Circular 91-70A, Oceanic and International Operations, 8/12/10, U.S. Department of Transportation
Advisory Circular 120-42B, Extended Operations (ETOPS and Polar Ops), 6/13/08, U.S. Department of Transportation
Advisory Circular 120-61A, In-flight Radiation Exposure, 7/6/06, U.S. Department of Transportation
Advisory Circular 135-42, Extended Operations (ETOPS) and Operations in the North Polar Area, 6/10/08, U.S. Department of Transportation
Finneran, Michael, Thousand-fold Rise in Polar Flights Hikes Radiation Risk, NASA Langley Research Center, 02.18.11
Geerts, B. and Linacre, E, The Height of the Tropopause, University of Wyoming, Atmospheric Science 11/97.
Joint Aviation Authorities JAR-OPS 1, Commercial Air Transportation (Aeroplanes), 10 May 2007
Jeppesen Airway Manuals, Arctic Polar / North Pacific High Altitude En Route Chart AP (HI) / NP (HI), 19 Sep 13
NAT Doc 001, Guidance and Information Material Concerning Air Navigation in the North Atlantic Region, Seventh Edition, January 2002.
Transport Canada Aeronautical Information Manual