192°(T) + 7E Var — Page 565, Lesson 566

Let’s start with the first one, item 170. We’ve got a true track of 192°(T), and a variation of 7° East. Remember, variation is the angular difference between true north and magnetic north. When it’s East variation, we subtract it from the true track to get the magnetic track. So 192°(T) minus 7°E gives us 185°(M)ag Track. That’s the track we want to fly over the ground, in magnetic terms. Now, we also have 5° of left drift. Drift is the angular difference between the heading you steer and the track you actually make over the ground, caused by wind. Left drift means the wind is pushing you to the left of your heading. To compensate, you need to aim off to the right by that same 5°. So we take the magnetic track of 185°(M) and add 5° to the right, giving us a magnetic heading of 190°(M). That’s the heading you’d steer on the compass to maintain the desired track. Now let’s move to item 171. This one is about grid navigation. The datum meridian is Greenwich, so the aircraft is 115° West of the datum, and we’re in the Northern hemisphere. Convergence is the angle between meridians as they meet at the pole. Here, convergence is 115° East. The rule is: Convergence East – True Least. That means when convergence is East, the true track is less than the grid track. So we take the grid track of 344°(G) and subtract the convergence of 115°, giving us 229°(T). So the true track is 229°. Now item 172. This is a rhumb line distance problem. A rhumb line is a line of constant bearing, and when two points are at the same latitude, the distance along that parallel is called the Departure. The formula is: Departure equals change of longitude in minutes, multiplied by the cosine of the latitude. Here, the change of longitude is 10°, so we convert that to minutes by multiplying by 60, giving 600 minutes. The latitude is 60°, and the cosine of 60° is 0.5. So 600 times 0.5 equals 300 nautical miles. That’s the departure distance. Item 173. This is about temperature at altitude. At FL410, which is 41,000 feet pressure altitude, the International Standard Atmosphere, or ISA, temperature is still -56.5°C, even though you’re above 36,090 feet. That’s the tropopause, where the temperature stops decreasing with altitude in the standard atmosphere. So if the SAT, which is Static Air Temperature, is -46.5°C, that’s the actual temperature you’d use. And you’d use the CRP-5, which is the flight computer, to work with these values. Item 174. Here we’re converting fuel flow. We have 22 US gallons per hour, and we need to convert that to imperial gallons. On the CRP-5, that conversion gives about 18.3 imperial gallons per hour. Then, using that value, you can calculate total endurance, either on the CRP-5 or with a calculator. Item 175. This is a two-part problem. Points A and B are at the same latitude but different longitudes, so that’s a departure problem again. Departure equals change of longitude in minutes times cosine latitude. The change is 1°, so 1 times 60 gives 60 minutes, and cosine of 60° is 0.5. So 60 times 0.5 equals 30 nautical miles. Now, points A and C are at different latitudes but the same longitude, so that’s a simple change of latitude problem. One degree of latitude is 60 nautical miles, so you’d just multiply the change in degrees by 60. Item 176 just says to use the CRP-5, so that’s a straightforward instruction for the calculation. Finally, item 177. We have 135 times 1.75, divided by 60, which equals 3.94. That’s a simple calculation, likely for a time or distance conversion. So, to recap: we’ve covered magnetic variation and drift correction, grid convergence with the True Least rule, departure and rhumb line distance, ISA temperature at high altitude, fuel conversion, and latitude change. Each of these is a core skill in general navigation.