Charting Your Course

Map reading can be defined as the action of a person matching man made or natural features with their corresponding symbols on a chart. Successful use of a map is solely dependent on the users ability or skill level in interpreting the map symbols, estimating distances and the availability of prominent landmarks.

The map most often used by general aviation pilots is the “sectional.” This map is especially popular to pilots who fly light aircraft over relatively short distances.

The sectional is printed at a 1 to 500,000 scale. In other words, one inch on the chart equals 500,000 inches on the earth’s surface (or approximately 8 miles).  For those cartographic purists, the sectional is printed in the Lambert conformal projection, thus each sectional represents a fairly small portion of the surface of the earth.  As a matter of fact it takes 37 sectionals to cover the continental U.S.

Sectionals show a great deal of data including color-coded topographical relief, cultural or man made features, as well as airport and special use airspace information. However this information is only useful when the map or chart is properly used.

It is suggested that when flying, align north on the chart with true north. Minnesota flight instructor Dan Boerner says, “In other words align your chart so that your desired track is pointing toward the nose of the aircraft.” This will assure that the landmarks on your route of flight will be in the same position as they are on the chart.

It is also important to remember to always work from the chart to the ground, finding the symbol on the chart and then locating that feature on the ground. This is helpful because the chart may not depict all of the surface features that might actually be seen.

When flying at low level, navigation by chart becomes more difficult. Air turbulence can affect your ability to make accurate instrument readings and increase the need to pay close attention to the aircraft’s fluctuating altitude. Also the terrain features or objects you use for reference will pass by much faster depending on the aircraft’s altitude above ground level (AGL).

It is vitally important to thoroughly study your charts if you plan to fly at low altitude. You must first do a thorough job of flight planning prior to takeoff. Also be extremely alert to obstructions and potential hazards like transmission towers, which can extend above 1,000 feet AGL. Be very alert to other low-level traffic. Dan Boerner adds, “Sectional charts show Maximum Elevation Figures (MEFs), which are the elevations above mean sea level, of the highest obstructions within each quadrangle, bounded by 30 minutes of latitude and 30 minutes of longitude.”

Finally, it should be remembered that natural features and landmarks could be altered in appearance during seasonal changes. For instance, bends in roads may be fully concealed by trees in the late spring through early fall. In the spring, creeks can become raging rivers whose breadth and course may change radically due to runoff and rain. Yet in midsummer to early fall, this same creek may dry up to be so small as to be dismissed by the pilot as a point of reference.

Small, relatively shallow lakes can dry up significantly in the heat of the summer, thus radically altering their shoreline contours and overall area. Trees could also hide the lake shoreline in the summer, and snow could completely erase landmarks, even lakes, from view in the winter.

Before taking off on a cross-country trip, sit down and plan your flight well. Pay close attention to the details that can affect your flight. Dan Boerner* reminds us to also include a review of all Special Use Airspace (SUA) in the proximity of, or on our proposed flight path. He indicates that pilots must determine if there is a need to circumnavigate a SUA, or contact Flight Service when 100 miles out to see if the SUA is active, or can be safely transited.

Study your charts so that you will develop a working familiarity with them including the features, obstructions, or potential hazards that may be located along the selected route of flight. By doing this you will be a more informed, proficient, and safe pilot.

EDITOR’S NOTE: Special thanks to Dan Boerner, CFI and Mn/DOT Aeronautics Airport Development Engineer, for his valuable input and suggestions for this article.

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This entry was posted in Education, June/July 2011, MN Aeronautics Bulletin, Sections and tagged , , , , , , , , . Bookmark the permalink.

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