Airways - Miscellaneous Charts — Page 188, Lesson 193

I want to walk you through the Atlantic Polar High Altitude En Route Chart, designated 5AT(HI). This is a specialised chart used primarily for planning routes and for high altitude polar navigation between Europe and North America. Let's start with when and how it's used. All operations between Europe and the Canadian Arctic Control Area, operating between Flight Level 280 and Flight Level 390 inclusive — that's FL280 to FL390 — are strongly recommended to flight plan in accordance with what's called the POLAR TRACK STRUCTURE, or PTS. The PTS is used during specific time windows: from 1200 to 1800 Zulu time for traffic heading to Alaska, and from 0000 to 0600 Zulu time for traffic heading to Europe. Now, what exactly is the Polar Track Structure? According to the North Atlantic Minimum Navigation Performance Specification Airspace Manual, Eighth Edition, the PTS consists of 10 fixed tracks in the Reykjavik Control Area, or Reykjavik CTA, and 5 fixed tracks through the Bodø Oceanic Control Area, or Bodø OCA. Those 5 tracks through Bodø are a continuation of the relevant PTS tracks in the Reykjavik CTA. Let's talk about the projection of this chart. It uses a Polar Stereographic projection. On this projection, bearings are correct — meaning the direction you measure from the chart is accurate. Great circles appear as straight lines in Polar Regions, which is very useful for plotting the shortest routes. And importantly, the scale is constant and correct in Polar Regions, so you can rely on distance measurements directly from the chart. Now, track direction on this chart can be given or measured in three ways: True, abbreviated T; Magnetic, abbreviated M; or Grid, abbreviated G. Grid navigation is something we'll cover later in the chapter, so I'll just mention it here for now. Let's look at magnetic variation. The lines of equal magnetic variation, called isogonals, printed on this chart are valid for the year 1995. On this chart, the North Magnetic Pole is located approximately at 78 degrees North, 100 degrees West — that's N78 W100. There is a rapid change of magnetic variation in this area. And here's a critical point: the directive force, which is the force that aligns a compass needle with the magnetic meridian, reduces to zero as the magnetic pole is approached. This means that in high latitudes, using magnetic reference for direction is impractical. Also, VOR beacons cannot be referenced to local magnetic north in these areas. Let me give you an example from the chart. Resolute Bay VOR, which operates on 112.1 MHz and has the identifier YRB, located at N74 degrees 43.7 minutes, W094 degrees 55.4 minutes — that VOR is aligned with local true north, not magnetic north. Finally, let's talk about distance measurement. Distances are printed parallel to the track segments on the chart. For other distances, you can measure using the nearest meridian scale, or you can use the scale printed at the top, left, and right edges of the chart. And note this conversion: 1 inch equals 100 nautical miles.