Introduction to Navigational Techniques
Pilotage, Reading Charts, Dead Reckoning, and Navigating with a Compass
Today's modern navigational equipment can guide an aircraft speeding miles above the earth precisely to its destination, often in the worst of weather, wind, and visibility. It's amazing, really, when you consider how early pilots navigated using only basic instruments, such as a compass, altimeter, stopwatch, and airspeed indicator, and by seeing landmarks on the ground.
There were other skills, of course. Some early pilots could approximate airspeed by listening to the pitch of the whining wires on their biplanes. They could gauge engine speed by the engine's rumble. They followed rivers and rails that swept beneath their wings. In short, the real world often served as the early pilot's most valuable flight and navigation instrument.
As far as navigation fundamentals are concerned, not much has changed in the past century of flight. Many of the navigational skills used by the early pilots form the foundation of present-day air navigation, and these are skills you can learn, practice, and perfect in Flight Simulator.
As each basic method is described below, keep in mind that rarely does a pilot navigate by using just one method. Most pilots rely on all four of the following basic techniques to navigate an airplane from departure to desired destination. Modern pilots, of course, use radio navigation and GPS to aid these basic methods.
In the first few decades of aviation, navigating in the air was called "avigation," and its practitioners, namely pilots, were known as "avigators." Here's how one early air navigation book summed up avigation:
"The purpose of avigation is to enable an aviator to determine the position of his aircraft on the earth's surface at any desired instant and the direction and distance from this position to the desired destination." —from Air Navigation by P.V.H. Weems (McGraw-Hill, New York, 1931)
A major point here is "at any desired instant." While navigating an airplane, the pilot always watches landmarks on the ground, the compass, the map, the clock, the air speed, and the ground speed. Navigation is not just something a pilot does before the flight, but actively does during the flight. Navigation is an ongoing process.
Pilotage: Following the Landmarks
Perhaps the most obvious way to navigate in Flight Simulator and the real world is to simply look out the window, comparing what you see on the ground with the chart in order to fix your position. This process, called pilotage, refers to navigating from place to place by following visual landmarks on the ground, such as roads, train tracks, rivers, lakes, mountains, and coastlines. It's that simple.
The airplane and automobile arose together, and early roads (and eventually highways) began spidering across the land, so pilots followed these known routes from the air. Railroad tracks, which already covered many areas, were another pilot favorite, and early fliers knew the rail lines as "the iron compass." The land itself was a welcome chart on clear days, and pilots used otherwise insignificant landmarks, such as small ponds or a stand of trees, for making final approaches and estimating glide slopes. The same is true today.
Tips for successful pilotage
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Reading the Chart
Pilotage and chart-reading are a natural pair. The general trick of reading a chart and navigating is learning the chart symbols and recognizing their real-world counterparts.
Chart-reading was not a requirement for becoming a pilot in the early days of aviation. In fact, there were no flight charts, merely flight instructions assembled by station managers and pilots, which were little more than basic flying directions that described flying from one prominent landmark to another—essentially a pilotage guide. Early flight instructions might have read: "From the runway follow the train tracks below, keeping the river and a large red barn on your left. Then fly toward a tall evergreen tree and a small town with a white train depot at the intersection of two roads..."
Before the advent of specific aviation charts, pilots often used roadmaps while flying. Even during the era of the first Piper Cubs in the 1940s and 1950s, pilots still relied on the auto roadmaps of their day as much as proper aviation charts, because roads, which pilots found easy to follow, were more clearly marked.
By the 1920s, however, aviation charts became widely available. Pilots sometimes pasted their charts to boards and strapped them to their legs for easy reference. Thus originated the term "kneeboard," describing equipment still used today by pilots as an easy way to view charts and checklist information during flight. Flight Simulator includes a kneeboard, which holds keeps your flight briefing, key commands, and aircraft checklists and speeds close at hand. You can easily display or hide the kneeboards during flights by pressing F10.
Early airmail and airline routes used aviation maps with the entire journey pieced together, map joining map, to form a full-length chart of the airway. These "strip maps" of airways were the same scale as today's sectional charts (1:500,000—or about 8 miles per inch) and guided pilots with landmarks, beacons, compass headings, and airports clearly and specially marked for aviators.
Today's busy aviation charts are contain markings for airports, navigational aids, airways, topographic features, major roads, rail lines and much more. Again, the key to reading maps for use with pilotage is knowing the chart symbols and learning to recognize their real-world counterparts.
Dead Reckoning: Mastering the Speed, Time, and Distance Equation
It's easy and fun to use pilotage and map reading to navigate, but when visibility turns poor, you can't always see your next—or any—landmark. Perhaps you're flying above the clouds, over water, or your landmarks are great distances apart. This is when a method called dead reckoning can help.
As commercial aviation came of age in the early 1930s, pilots recognized that the most efficient and fastest route between two points was not by following a winding road or meandering river, but by flying a straight line. Harvey H. Holland, a captain in the Army Air Corps and author of Avigation (McGraw-Hill, 1931), summed it up like this:
"When the pilot is obliged to follow railways, highways, and streams, he loses the advantage of the direct air route and advertises his lack of information in one of the most important phases of the science in which he is engaged."
A Sample Use of Dead Reckoning A plane takes off and flies at 100 mph for 3 hours on a straight course with no wind. To find the position of the aircraft using dead reckoning, use this simple equation: Speed (ground speed) x Time (since a known point) = Distance (from the same known point) -or- ST = D Remember: If you know any two of the three variables, you can find the third. If you want to estimate time, for instance, the equation becomes D/S=T. If you want to estimate ground speed, the equation changes to D/T=S. The dead reckoning calculation in the above example therefore goes: 100 mph x 3 hours = 300 miles By calculating the dead reckoning equation often, a pilot can keep a record of the aircraft's course and distance from a known position. Be sure to begin counting time and gauging velocity at a known position. If you inaccurately fix your point of departure, all other calculations will be incorrect. |
Dead reckoning isn't as bad as it sounds. First of all, there's nothing dead about it—the term refers to actively plotting and calculating your course heading and elapsed time in order to compute distance traveled to estimate your position. Alternate spellings, "ded reckoning" or "de'd reckoning," reveal the term's origin: "deduced reckoning." Reckoning is just another word for calculating, so dead reckoning (or deduced calculating) refers to the process of estimating your position by computations based on airspeed, course, heading, wind direction, air speed, ground speed, and elapsed time. Essentially, you are figuring out where you are and where you will be at a certain time if you hold the ground speed and compass course you travel. The main instruments that will help are your clock and your compass.
Calculating Ground Speed
You can calculate ground speed—an aircraft's speed relative to the ground—using the equation D/T=S. Ground speed, not airspeed, is the crucial variable in dead reckoning, since you're plotting progress along the ground. With no wind, an aircraft flying at 100 knots in the air travels 100 knots relative to the ground. If an aircraft traveling at 100 knots of airspeed has a 25-knot headwind, however, its ground speed would be just 75 knots. Conversely, if a plane flying with 100 knots of airspeed has a 25-knot tailwind, its ground speed would be 125 knots.
The problem gets more complex when the wind is not blowing directly at the nose or tail of the aircraft. A simple way to estimate your ground speed using dead reckoning is to note the time since departure and the distance to a known landmark. When you get to the landmark, calculate your speed (D/T=S). That will be your ground speed—because it's based on the true distance over land and actual time it took to get there. By comparing your ground speed and airspeed (as displayed on your airspeed indicator), you will see the effects of wind on your ground speed, no matter which direction it's blowing.
Points of Dead Reckoning
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Navigating with a Compass: Don't Lose Your Heading
Magnetic Compass |
Following a compass heading is an integral part of dead reckoning, as well as every other navigational technique. In fact, the compass is one of the oldest navigational instruments around.
A magnetic compass responds to the earth's magnetic field, which attracts the north end of the compass needle; the needle always points north. Magnetic north, that is. Most old aircraft are equipped with only a compass, while modern aircraft employ a compass and a heading indicator (directional gyro), which is easier to use, but must always be adjusted to match the compass for an accurate reading.
What is a Compass Heading?
A compass heading indicates the direction your aircraft is pointed relative to magnetic north.
Magnetic Variation
Magnetic variation is the difference between the true North Pole (earth's rotational axis) and the magnetic north pole (where the earth's lines of magnetic force converge). In many places of the world, the lines of longitude, which point true north, and the lines of magnetic force, which point toward magnetic north are not aligned. The difference between the compass magnetic indication and true north is known as magnetic variation.
Reading the Compass
To display or hide the magnetic compass, press SHIFT+5.
In an aircraft compass, the needle is attached to a compass card, which shows direction in degrees, marked by lines, numbers, and the letters N, S, E, and W, which represent north, south, east, and west, respectively. The compass card is divided into 360 degrees with north, south, east, and west marked at 90-degree intervals, such that North marks both 0 and 360 degrees (beginning and end) of the compass continuum. East is 90 degrees; south is 180 degrees; west is 270 degrees.
Determining Your Compass Heading
Read your aircraft's compass heading under the vertical lubber line that runs down the front of the compass window. For example, when you fly a heading of due magnetic north, the N will be directly beneath the lubber line.
Turning to a Compass Heading
You know that when you face north, east is to your right, west is to your left, and south is behind. But notice that on your aircraft compass the easterly headings are to the left of north, and westerly headings are to the right of north.
The reason is simple: The N that's printed on the compass card is actually on the card's south-facing side. That's so you can see it. The same is true for east, west, and south—each is marked on the side opposite their true direction. Therefore, when you turn to a compass heading, you turn the aircraft in the direction opposite the marked compass heading you wish. Remember: The airplane moves, not the compass. For example, when you turn from a heading of due magnetic north to a heading of due magnetic east, just turn the airplane to the right even though the easterly headings are marked on the compass' left side. Your course change will be complete when the E lies beneath the lubber line.
Compass Turning Errors
Compass turning errors occur due to the oblong shape of the earth's magnetic field, which dips toward the earth at the poles. This affects your compass in the following ways:
- Northerly Turning Error: As the airplane turns from or through a northerly heading, the compass initially indicates a turn in the opposite direction, and then shows a heading that lags the aircraft's true heading.
- Southerly Turning Error: As the airplane turns from or through a southerly heading, the compass shows a heading that leads the aircraft's true heading.
- As the airplane approaches an easterly or a westerly heading, the compass error lessens. When turning through a due east (90 degrees) or a due west (270 degrees) heading, there is no compass error.
Once stabilized in straight-and-level flight after a turn, the compass will indicate your actual magnetic heading. Turning errors only occur during a turn. A magnetic compass is most accurate in straight-and-level flight.
Note: Compass errors in the southern hemisphere are the opposite of compass errors in the northern hemisphere.
Acceleration and Deceleration Errors
The compass will read an error when you accelerate or decelerate on an easterly or westerly heading. When accelerating, your compass will indicate a heading which is more northerly than your true course. When decelerating, your compass will indicate a heading which is more southerly than your true course. An acronym proves an easy memory aid: ANDS—Accelerate North, Decelerate South.
Why such acceleration and deceleration errors? The aircraft's change in speed causes the compass card to tilt, which makes the compass unable to correct for the earth's dipping magnetic field. Because the compass needle's north end tries to align itself with the earth's dipping magnetic field, the compass card turns, thus indicating an incorrect heading. These errors only occur while accelerating or decelerating. When flying at a constant velocity, no such errors occur.
Heading Indicator (Directional Gyro or DG)
Such mental gymnastics are why the Heading Indicator or Directional Gyro (sometimes called DG) is easier to use than the magnetic compass. Unlike the magnetic compass, the heading indicator corresponds directly to your turns. Headings that are to the right in the real world are also to the right on the heading indicator. Just turn the airplane toward the heading you wish to fly until the nose of the airplane in the heading indicator points to your desired heading. This works as long as the heading indicator is set to match the magnetic compass. The heading indicator is a gyroscopic instrument, not magnetic, so it does not respond to the earth's magnetic field. But the heading indicator is subject to an error known as "gyroscopic precession," which means that you must set the heading indicator to match the magnetic compass's heading before each flight and reset it to the compass at regular intervals during flight to keep the two instruments synchronized.
Correcting for Wind Drift
Remember that dead reckoning does not figure wind drift into the navigational equation. Real-world pilots use mechanical or electronic flight computers to calculate headings to compensate for wind drift, and many pioneer aviators referred to tables. We'll keep wind correction simple, though. When correcting for wind drift, simply turn into the wind, much as you would swim straight across a river by slightly angling upstream. Keep this in mind, but also keep your eyes on the landmarks below, using your pilotage skills.
To display wind direction and speed, press SHIFT+Z.
Flying a particular compass heading is known as flying a course. But because wind pushes an aircraft in flight, the compass heading does not necessarily reflect the aircraft's true path over the ground, which is known as the aircraft's track. For example, if you wish to fly due east over the ground, but the wind is blowing from the north, you must turn the aircraft slightly into the wind (slightly toward the north) to correct for wind drift. As a result, your track over the ground will be due east, while your compass heading will indicate you are flying somewhat northeasterly.
The simple way to see if you're drifting off course due to a crosswind:
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Using All the Navigational Methods All the Time
Ultimately, the true art of navigation involves using as many navigational techniques as you can throughout the flight. With each navigational method you use comes increased certainty of aircraft position and the assurance of keeping on course toward your desired destination. Charles Lindbergh was known for his methodical navigation: His eyes moved from map, to landmarks below, to instrument panel, to map, and so on. He continuously practiced dead reckoning. Every moment he compared what he saw on the map to the world beneath his wings.
And it's a good idea to practice all methods, even when the visibility is good and you are within easy sight of land and landmarks. It keeps your dead reckoning skills in practice and nearly second-nature, which is a good idea, because there's nothing more unpredictable than the weather.
Other Ways to Navigate in Flight Simulator
Although pilotage, dead reckoning, and using a compass form the foundation of air navigation, there are other ways to navigate in Flight Simulator, such as using radio navigation (VOR) and the GPS. For more information about other navigation methods, see the Navigation section.
Learning More about Air Navigation
Many books cover the topic of air navigation. To learn more about the navigational points covered above, read Rod Machado's Private Pilot Handbook and King Schools' Cleared for Takeoff.
Tips for Old-Fashioned Navigation in Flight Simulator
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