Plotting — Page 478, Lesson 474

Right, let's get into the plotting section of your General Navigation. This is where we move from theory into the practical business of putting marks on a chart. First, let's set the scene. You've already met two very different ways of navigating. On one end, you have solo-pilot VFR flying, which leans on the 1 in 60 rule. On the other end, you have the big jets with automatic systems like INS, IRS, FMS, GPS, and RNAV. But there's a whole middle ground of aircraft. These are more sophisticated than a light trainer but not quite the full glass-cockpit airliner. These intermediate aircraft are routinely fitted with VOR, DME, ADF, and a Slaved Gyro Compass. For this class of aircraft, you need to plot your position and tracks on a chart. You'll use a Radio Navigation chart or a specialist plotting chart, which is usually a Mercator's chart or a Lambert's Conical Orthomorphic chart. Now, for the EASA ATPL, the requirement is specifically for the Lambert's Conical Orthomorphic, and occasionally the Polar Stereographic. So the techniques we'll cover are for those two, not for Mercator's. The charts used for most of the exam questions are the Jeppesen E(LO)1 and 2, and the E(LO)1A. And a very practical point: if you're sitting the EASA exams, you must bring your own copy of each chart, because the CAA will not provide them at the exam venue. Before we plot anything, you need the right kit. The equipment list for this section is: a navigational computer, a navigational straight-edge, a plotting protractor of the square type, compass/dividers, and 2H and HB pencils for plotting and writing, plus a soft eraser. Now, let's talk about the fundamental datum. Plotting is normally carried out using true north as the datum. It is possible to plot some types of radio bearing directly in magnetic without converting to true, but usually, true tracks and bearings are used. So keep that in mind as the default. Let's define our terms precisely. First, Heading. This is the direction in which the nose of the aircraft is pointing, measured in degrees from 000 to 360, clockwise. It's measured from true, magnetic, or compass north, and the abbreviations are Hdg(T), Hdg(M), or Hdg(C). Now, the key conversions: if you're given Hdg(M), you must convert it to true by taking into account the variation on the chart. If you're given Hdg(C), you must convert it to true by taking into account both variation and deviation. So remember, magnetic to true needs variation; compass to true needs variation and deviation. Next, a Fix. This is the ground position of the aircraft, obtained from two or three visual or radio position lines, or by radar. So it's your confirmed position on the ground. And finally, a Position Line. This is a line somewhere along which the aircraft is known to be at a particular time. You know you're on that line, but you don't know exactly where on it until you cross it with another one. That's the foundation set. We have our datum, our heading definitions, and the difference between a fix and a position line. Now we can start building on that.