Airplane pilots navigate by pilotage (flying by reference to ground landmarks) or dead reckoning (computing a heading from true airspeed and wind, and then estimating time needed to fly to a destination). Glider pilots use pilotage since they generally cannot remain on a course line over a long distance and do not fly one speed for any length of time. Nonetheless, it is important to be familiar with the concepts of dead reckoning since a combination of the two methods is sometimes needed.
Using the Plotter
Measuring distance with the plotter is accomplished by using the straight edge. Use the Albuquerque sectional chart and measure the distance between Portales Airport (Q34) and Benger Airport (Q54), by setting the plotter with the zero mark on Portales. Read the distance of 47 nautical miles (NM) to Benger. Make sure to set the plotter with the sectional scale if using a sectional chart (as opposed to the WAC scale), otherwise the measurement will be off by a factor of two. [Figure 11-5]
The true heading between Portales and Benger can be determined by setting the top of the straightedge along the course line, then slide it along until the index hole is on a line of longitude intersecting the course line. Read the true heading on the outer scale, in this case, 48°. The outer scale should be used for headings with an easterly component. If the course were reversed, flying from Benger to Portales, use the inner scale, for a westerly component, to find 228°. [Figure 11-6]
A common error when first using the plotter is to read the course heading 180° in error. This error is easy to make by reading the scale marked W 270° instead of the scale marked E 09°. For example, the course from Portales to Benger is towards the northeast, so the heading should be somewhere between 30° and 60°, therefore the true heading of 48° is reasonable.
A Sample Cross-Country Flight
For training purposes, plan a triangle course starting at Portales Airport (PRZ), with turn points at Benger Airport (X54), and the town of Circle Back. As part of the preflight preparation, draw the course lines for the three legs. Using the plotter, determine the true heading for each leg, then correct for variation and make a written note of the magnetic heading on each leg. Use 9° east (E) variation as indicated on the sectional chart (subtract easterly variations, and add westerly variations). The first leg distance is 47 NM with a heading of 48° (48° – 9° E = 39° magnetic); the second leg is 38 NM at 178° true (178° – 9° E = 169° magnetic); the third leg is 38 NM at 282° true (282° – 9° E = 273° magnetic). [Figure 11-7]
Assume the base of the cumulus is forecast to be 11,000 MSL, and the winds aloft indicate 320° at 10 knots at 9,000 MSL and 330° at 20 knots at 12,000 MSL. Make a written note of the winds aloft for reference during the flight. For instance, the first leg has almost a direct crosswind from the left; on the second leg, a weaker crosswind component from the right; while the final leg is almost directly into the wind. Knowing courses and approximate headings aids the navigation and helps avoid getting lost, even though deviations to stay with the best lift are needed. During the flight, if the sky ahead shows several equally promising cumulus clouds, choosing the one closest to the course line makes the most sense.
During preflight preparation, study the course line along each leg for expected landmarks. For instance, the first leg follows highway and parallel railroad tracks for several miles before the highway turns north. The town of Clovis should become obvious on the left. Note the Class D airspace around Cannon Air Force Base (CVS) just west of Clovis—this could be an issue if there is better soaring north of course track because of military traffic operating into Cannon. With the northwesterly wind, it is possible to be crossing the path of aircraft on a long final approach to the northwest-southeast runway at the air base.
Next is the Clovis airport (CVN) with traffic to check operating in and out of the airport. Following Clovis are Bovina and Friona; these towns can serve as landmarks for the flight. The proximity of the Texico (TXO) VOR, a VHF Omnidirectional Range station near Bovina, indicates the need for alertness for power traffic in the vicinity. The VOR serves as an approach aid to the Clovis airport.
The first turn point is easy to locate because of good landmarks, including Benger Airport (X54). [Figure 11-8] The second leg has fewer landmarks. After about 25 miles, the town of Muleshoe and the Muleshoe airport (2T1) should appear. The town should be on the right and the airport on the left of the intended course. Next, the course enters the Bronco 1 Military Operations Area (MOA). The dimensions of the MOA can be found on the sectional chart, and the automated flight service station (AFSS) should be consulted concerning the active times of this airspace. Approaching the second turn point, it is easy to confuse the towns of Circle Back and Needmore. [Figure 11-9] The clues are the position of Circle Back relative to an obstruction 466 feet above ground level (AGL) and a road that heads north out of Needmore. Landmarks on the third leg include power transmission lines, Salt Lake (possibly dry), the small town of Arch, and a major road coming south out of Portales. About eight miles from Portales a VOR V-280 airway is crossed.
After a thorough preflight of the glider and all the appropriate equipment is stowed or in position for use in flight, it is time to go fly. Once in the air and on course, try to verify the winds aloft. Use pilotage to remain as close to the course line as soaring conditions permit. If course deviations become necessary, stay aware of the location of the course line to the next turn point. For instance, the Cu directly ahead indicates lift, but the one 30° off course indicates possibly even more lift, it may be better not to deviate. If the Cu left of course indicates a possible area of lift compared to the clouds ahead and only requires a 10° off course deviation, proceed towards the lift. Knowing the present location of the glider and where the course line is located is important for keeping situational awareness.
Sometimes it is necessary to determine an approximate course once already in the air. Assume a few miles before reaching the town of Muleshoe, on the second leg, the weather ahead is not as forecast and has deteriorated—there is now a shower at the third turn point (Circle Back). Rather than continuing on to a certain landing in the rain, the decision is made to cut the triangle short and try to return directly to Portales. Measure and find that Portales is about 37 miles away, and the estimated heading is about 240°. Correct for variation (9°) for a compass heading of about 231° (240° – 9° = 231°). The northwesterly wind is almost 90° to the new course and requires a 10° or 20° crab to the right, so a heading between 250° and 270° should work, allowing for some drift in thermal climbs. With practice, the entire thought process should take little time.
The sky towards Portales indicates favorable lift conditions. However, the area along the new course includes sand hills, an area that may not have good choices for off-field landings. It may be a good idea to fly more conservatively until beyond this area and then back to where there are suitable fields for landing. Navigation, evaluation of conditions ahead, and decision-making are required until arrival back at Portales or until a safe off-field landing is completed.
Navigation Using GPS
The GPS navigation systems are available as small hand-held units. (See Chapter 4, Flight Instruments, for information on GPS and electronic flight computers.) Some pilots prefer to use existing flight computers for final glide and speed-tofly information and add a hand-held GPS for navigation. A GPS system makes navigation easier. A GPS unit displays distance and heading to a specified point, usually found by scrolling through an internal database of waypoints. Many GPS units also continuously calculate and display ground speed. If TAS is also known, the headwind component can be calculated from the GPS by subtracting ground speed from TAS. Many GPS units also feature a moving map display that shows past and present positions in relation to various prominent landmarks like airports. These displays can often zoom in and out to various map scales. Other GPS units allow marking a spot for future reference. This feature can be used to mark the location of a thermal before going into a turn point, with the hopes that the area will still be active after rounding the turn point.
One drawback to GPS units is their attractiveness—it is easy to be distracted by the unit at the expense of flying the glider and finding lift. This can lead to a dangerous habit of focusing too much time inside the cockpit rather than scanning outside for traffic. Like any electronic instrument, GPS units can fail, so it is important to have a backup for navigation, such as a sectional and plotter.