SATCOM / CPDLC

[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 data link 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.

Navigation Issues

Magnetic Variation and Convergence of the Meridians

[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.

True Heading

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.

GPS Navigation

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:

$\mathrm{Height\; Above\; Pole}=10998cos55-6887=2122$

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:

$\mathrm{Minimum\; Latitude\; to\; See\; Pole}=arcsin(6887/10998)=39$

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.

Temperature Issues

Tropopause Height and ISA

[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.

Surface Temperatures

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.

Fuel Freezing

[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.

Polar Radiation

[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.

[NASA Study, Michael Finneran]

• 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.

Alternate Airports

[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.

References

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 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

FAA Orders 8400 and 8900

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

Wikimedia Commons.