When in flight, orient the chart so that north on the chart is toward true north (TN). The course line on the chart is then aligned with the intended course of the aircraft so that landmarks on the ground appear in the same relative position as the features on the chart. Obtain the approximate position of the aircraft by DR. Select an identifiable landmark on the chart at or near the DR position. It is important to work from the chart to the ground. Identify the landmark selected and fix the position of the aircraft. The importance of a good DR cannot be over emphasized. When there is any uncertainty of position, every possible detail should be checked before identifying a checkpoint.
The relative positions of roads, railroads, airfields, and bridges make good checkpoints. Intersections and bends in roads, railroads, and rivers are equally good. When a landmark is a large feature, such as a major metropolitan area, select a small prominent checkpoint within the large landmark to fix the position of the aircraft. When a landmark is not available as a reference at a scheduled turning point, make the turn on the estimated time of arrival (ETA). Extend the DR position to the next landmark and fix the position of the aircraft to make sure the desired course and GS are being maintained. Remember, the desired magnetic course on any given leg corrected for drift is the magnetic heading which parallels course. This helps to keep from getting any farther off course.
Map Reading While Flying At Low Altitudes
When flying at lower altitudes, additional difficulties may be encountered. Turbulence increases the difficulty of reading instruments. Depending on the aircraft’s altitude above ground level (AGL), the circle of visibility can be greatly reduced, and those objects that are visible pass by so rapidly only the largest landmarks can be easily identified.
In low altitude navigation, flight planning is especially important as there is little time for inflight computations. An important part of good flight planning is proper chart preparation. Normally radius-of-turn procedures are used when drawing the chart, but depending on your tactics, point to point is also an option. Time elapsed marks and distance remaining marks along the course line of each leg gives navigators a running DR with the aid of a stopwatch.
In low altitude flight, one should be particularly alert to possible danger from obstructions. Hills and mountains are easily avoided if the visibility is good. Radio and television towers, which may extend as much as 1,000 feet or more into the air, often from elevated ground, are less conspicuous. All such obstructions may or may not be shown on the aeronautical charts. Flights need to be above the highest elevation listed for that grid square on the sectional chart to ensure obstruction clearance. Maximum elevation figures (MEF) are explained on the inside panel (left side) of the sectional chart.
Map Reading at Night
At night, unlighted landmarks may be difficult or impossible to see. Lights can be confusing because they appear closer than they really are. Fixing on points other than those directly beneath the aircraft is very difficult. Objects may be more easily seen by scanning or looking at them indirectly to eliminate the eye’s visual blindspot. Preserve night vision by working with red or green light, being aware that red light can detract from the chart color. Moonlight makes it possible to see prominent landmarks like land-water contrast. Reflected moonlight often causes a river or lake to stand out brightly for a moment, but this condition is usually too brief for accurate fixing. Roads and railroads may be seen after the eyes are accustomed to the darkness. Lighted landmarks, such as cities and towns, stand out more clearly at night than in daytime. Large cities can often be recognized by their distinctive shapes. Many small towns are dark at night and are not visible to the unaided eye. Some airfields have distinctive light patterns and may be used as checkpoints. Military fields use a double white and single green rotating beacon, while civilian fields use a single white and single green rotating beacon. Busy highways are discernible because of automobile headlights.