VHF Omnidirectional Range (VOR)
Global Positioning System (GPS)
Air navigation is the art of directing an aircraft along a desired course and being able to determine its geographical position at any time. Such navigation may be accomplished by pilotage, dead reckoning, or using radio navigational aids.
Pilotage is the use of visible landmarks to maintain a desired course, and is the basic form of navigation for the beginning pilot operating under visual flight rules (VFR). Visible landmarks which can be identified on aeronautical charts allow the pilot to proceed from one check point to the next.
The aeronautical charts most commonly used by VFR pilots are the VFR Sectional Aeronautical Chart, the VFR Terminal Area Chart, and the World Aeronautical Chart. All three charts include aeronautical information such as airports, airways, special use airspace, and other pertinent data.
The scale of the VFR Sectional Aeronautical Chart is 1:500,000 (1 inch = 6.86 NM). Designed for visual navigation of slow speed aircraft in VFR conditions, this chart portrays terrain relief and checkpoints such as populated places, roads, railroads, and other distinctive landmarks. These charts have the best detail and are revised every 6 months.
Information found on the VFR Terminal Area Chart is similar to that found on the VFR Sectional Chart, but the scale on this chart is 1:250,000 (1 inch = 3.43 NM). These charts are for a specific city with Class B airspace. They show much detail, but have small coverage.
The World Aeronautical Chart has a scale of 1:1,000,000, which is more convenient for use in navigation by moderate speed aircraft. It depicts cities, railroads, and distinctive landmarks, etc. These charts have less detail and are revised no more than once a year.
To identify a point on the surface of the earth, a geographic coordinate, or grid, system was devised. By reference to meridians of longitude and parallels of latitude, any position may be accurately located when using the grid system.
Equidistant from the poles is an imaginary circle called the equator. The lines running east and west, parallel to the equator are called parallels of latitude, and are used to measure angular distance north or south of the equator. From the equator to either pole is 90°, with 0° being at the equator; while 90° north latitude describes the location of the North Pole. See Figure 7-1.

Figure 7-1. Meridians of longitude and parallels of latitude
Lines called meridians of longitude are drawn from pole to pole at right angles to the equator. The prime meridian, used as the zero degree line, passes through Greenwich, England. From this line, measurements are made in degrees both easterly and westerly up to 180°.
Any specific geographical point can be located by reference to its longitude and latitude. For example, Washington, DC is approximately 39° north of the equator and 77° west of the prime meridian and would be stated as 39°N 77°W. Note that latitude is stated first.
In order to describe a location more precisely, each degree (°) is subdivided into 60 minutes (') and each minute further divided into 60 seconds ("), although seconds are not shown. Thus, the location of the airport at Elk City, Oklahoma is described as being at 35°25'55"N 99°23'15"W (35 degrees, 25 minutes, 55 seconds north latitude; 99 degrees, 23 minutes, 15 seconds west longitude). Degrees of west longitude increase from east to west. Degrees of north latitude increase from south to north.
Time is measured in relation to the rotation of the earth. A day is defined as the time required for the earth to make one complete revolution of 360°. Since the day is divided into 24 hours, it follows that the earth revolves at the rate of 15° each hour. Thus, longitude may be expressed as either 90° or 6 hours west of Greenwich.
Twenty-four time zones have been established. Each time zone is 15° of longitude in width, with the first zone centered on the meridian of Greenwich. Each zone uses the local time of its central meridian as shown in FAA Figure 27.
For example, when the sun is above the 90th meridian, it is noon central standard time (CST). At the same time it is 6 p.m. Greenwich, 11 a.m. mountain standard time (MST), and 1 p.m. eastern standard time (EST). When daylight saving time (DST) is in effect, the sun is over the 75th meridian at noon CST.
Most aviation operations time is expressed in terms of the 24-hour clock, (for example, 8 a.m. is expressed as 0800; 2 p.m. is 1400; 11 p.m. is 2300) and may be either local or Coordinated Universal Time (UTC). UTC is the time at the prime meridian and is represented in aviation operations by the letter “Z,” referred to as Zulu time. For example, 1500Z would be read as “one five zero zero Zulu.”
In the United States, conversion from local time to UTC is made in accordance with the table in the lower left corner of FAA Figure 27.
Problem: An aircraft departs an airport in the Pacific standard time zone at 1030 PST for a 4-hour flight to an airport located in the central standard time zone. The landing should be at what coordinated universal time (UTC)?
Solution: Use the conversion table in FAA Figure 27 and the following steps:
Convert 1030 PST to UTC:
|
1030 |
PST (takeoff time) |
|
+ 0800 |
(conversion) |
|
1830 |
UTC |
Add the flight time.
|
1830 |
UTC |
|
+ 0400 |
(flight time) |
|
2230 |
UTC (time the aircraft should land) |
A VFR Sectional Aeronautical Chart is a pictorial representation of a portion of the Earth’s surface upon which lines and symbols in a variety of colors represent features and/or details that can be seen on the Earth’s surface. Contour lines, shaded relief, color tints, obstruction symbols, and maximum elevation figures are all used to show topographical information. Explanations and examples may be found in the chart legend. Pilots should become familiar with all of the information provided in each Sectional Chart Legend, found in FAA Legend 1.
Dead reckoning is the method used for determining position with a heading indicator and calculations based on speed, elapsed time, and wind effect from a known position. The instruments used for dead reckoning navigation include the outside air temperature gauge, the airspeed indicator, the altimeter, the clock, and the magnetic compass system or slaved gyro system. These instruments provide information concerning direction, airspeed, altitude, and time, and must be correctly interpreted for successful navigation.
A course is the direction of flight measured in degrees clockwise from north. Meridians of longitude run from the south pole to the north pole. This alignment is called true north. When a course is plotted on a chart in relation to the lines of longitude and/or latitude it is called a true course (TC), and will be expressed in three digits. North may be either 360° or 000°; east is 090°; south is 180°; and west is 270°. Any attempt to project lines of latitude and longitude onto a flat surface such as a chart results in a certain amount of distortion. When plotting a course on a sectional aeronautical chart, this distortion may be minimized by measuring true course in reference to the meridian nearest to the halfway point between the departure point and the destination.
A common type of plotter that is used to plot a course is shown in Figure 7-2. This plotter is a semi-circular protractor with a straight edge attached to it. The straight edge has distance scales that match various charts and these scales may depict both statute and nautical miles. A small hole at the base of the protractor portion indicates the center of the arc of the angular scale. Two complete scales cover the outer edge of the protractor, and they are graduated in degrees. An inner scale measures the angle from the vertical.

Figure 7-2. Placing the plotter on the course line
To determine true course, use the plotter in the following manner:
The north pole where all meridians converge is true north. The north pole which attracts the needle of a compass is magnetic north. These two poles are not in the same place. At any point where magnetic north and true north are in line with each other, the compass needle points both to magnetic north, and coincidentally, true north. The line along which this occurs is known as the agonic line. When positioned west of the agonic line, a compass will point right (east) of true north. When positioned east of the agonic line, a compass will point left (west) of true north. This angular difference between true north and magnetic north is called magnetic variation (VAR). West of the agonic line, variation is “easterly.” East of the agonic line, variation is “westerly.”
The amount and direction of variation is depicted on sectional charts as dashed magenta colored lines connecting points of equal variation, called isogonic lines.
A course measured on a sectional chart is a true course: it is measured from a meridian, which runs from the south pole to the north pole. Since a magnetic compass is used to maintain a course while flying, this true course must now be converted to a magnetic course (MC). This conversion is made by either adding or subtracting the variation. To convert a TC to an MC, subtract easterly variation and add westerly variation: “East is least, west is best.”
TC ± VAR = MC
The magnetic compass is affected by influences within the aircraft such as electrical circuits, radios, engines, magnetized metal parts, etc., which cause the compass needle to be deflected from its normal reading. This deflection is known as deviation (DEV), and it must be applied to convert a magnetic course to a compass course (CC) to make it usable in flight.
Deviation, which is different for each aircraft, may also vary for different courses in the same airplane. To let the pilot know the appropriate correction, a correction card is mounted near the compass.
To determine the actual compass reading to be followed during flight, it is necessary to apply the corrections for both variation and deviation:
True course ± variation = magnetic course ± deviation = compass course
or,
TC ± VAR = MC ± DEV = CC.
An additional computation, common to both pilotage and dead reckoning, is necessary to compensate for the effect of wind.
Wind direction is reported as the direction from which the wind blows, i.e., wind blowing from the west to the east is a west wind. Wind speed is the rate of motion without regard to direction. In the United States, wind speed is usually expressed in knots. Wind velocity includes both direction and speed of the wind; for example, a west wind of 25 knots.
Downwind movement is with the wind; upwind movement is against the wind. Moving air exerts a force in the direction of its motion on any object within it. Objects that are free to move in air will move in a downwind direction at the speed of the wind.
If a powered aircraft is flying in a 20-knot wind, it will move 20 nautical miles downwind in 1 hour in addition to its forward movement through the air. The path of an aircraft over the earth is determined both by the motion of the aircraft through the air and by the motion of the air over the earth’s surface. Direction and movement through the air is governed both by the direction that the aircraft nose is pointing and by aircraft speed.
The sideward displacement of an aircraft caused by wind is called drift. Drift can be determined by measuring the angle between the heading (the direction in which the nose is pointing) and the track (the actual path of the aircraft over the earth). See Figure 7-3.
For example, Figure 7-3 shows an aircraft which departs point A on a heading of 360° and flies for 1 hour in a wind of 270° at 20 knots. Under a no-wind condition the aircraft would arrive at point B at the end of 1 hour. However, this example has a wind of 20 knots, and the aircraft moves with the wind; so at the end of 1 hour, the aircraft is at point C, 20 nautical miles downwind from B. From A to B is the intended path of the aircraft, from B to C is the motion of the body of air, and from A to C is the actual path of the aircraft over the earth (the track).

Figure 7-3. Drift
A given wind will cause a different drift on each aircraft heading and it will also affect the distance traveled over the ground in a given time. With a given wind, the ground speed varies with each different aircraft heading. Figure 7-4 illustrates how a wind of 270° at 20 knots would affect the ground speed and track of an aircraft on various headings. In this particular illustration, on a heading of 360°, drift would be to the right; on a heading of 180°, drift would be to the left. With a 90° crosswind and no heading correction applied, there would be little effect on ground speed. On a heading of 090°, no left or right drift would be experienced; instead, the ground speed would be increased by the tailwind. On a 270° heading, the ground speed would be reduced by the headwind.

Figure 7-4. Different effects of wind on track and ground speed
By determining the amount of drift, a pilot can counteract the effect of wind and make the track of the aircraft coincide with the desired course. For example, if the wind is from the left, the correction would be made by pointing the aircraft to the left a certain number of degrees, thereby compensating for wind drift. This is the wind correction angle (WCA), and it is expressed as degrees left or right of the course. See Figure 7-5.
Any course, true, magnetic, or compass, becomes a heading when it is corrected for wind. See Figure 7-6.

Figure 7-5. Compensating for wind drift

Figure 7-6
True course is determined by measuring the course on an aeronautical chart. True airspeed is known by applying the appropriate correction to the indication of the airspeed indicator. The wind direction and velocity are known from reports or forecasts from Flight Service Stations.
The true heading and the ground speed can be found by drawing a wind triangle of vectors. One side of the triangle is the wind direction and velocity, one side is the true heading and true airspeed, the final side is the track, or true course, and the ground speed. Each side of a wind triangle is the vector sum of the other two sides.
Note: ASA’s CX-3 is an electronic flight computer and can be used in place of the E6-B. This aviation computer can solve all flight planning problems, as well as perform standard mathematical calculations.
The WCA required to change a course to a heading can be found by using the wind face of the E6-B. Ground speed can also be determined as a part of this procedure.
The wind face of the E6-B consists of a transparent, rotatable plotting disk mounted in a frame as shown in Figure 7-7. A compass rose is located around the plotting disk (Figure 7-7a). A correction scale on the top of the frame is graduated in degrees left and right of the true index (Figure 7-7b), and it is used for calculating drift correction. A small reference circle, called a grommet, is located at the center of the plotting disk (Figure 7-7c).

Figure 7-7. Wind face of E6-B computer
A sliding grid (Figure 7-7d) inserted behind the plotting disk is used for wind computations. The slide has converging lines (track or drift lines) which indicate degrees left or right of center (Figure 7-7e). Concentric arcs (speed circles) on the slide are used for calculations of speed (Figure 7-7f). The wind correction angle and ground speed may be found when true course, true airspeed, wind speed and wind direction (relative to true north) are known.
Problem: Using a flight computer and the following conditions, find the WCA, the true heading (TH), and the ground speed (GS).
Conditions:
True course (TC): 090°
True airspeed (TAS): 120 knots
True wind direction: 160°
Wind speed: 30 knots
Solution:

Figure 7-8. Plotting wind speed and wind direction

Figure 7-9. Determining the wind correction angle and ground speed
Determine the true heading by applying the formula:
TC + WCA = TH
In this case the wind correction is to the right, so it will be added to the true course:
|
090° |
(TC) |
|
+ 14° |
(WCA) |
|
104° |
(TH) |
Opposite the windface of the flight computer is a circular slide rule or calculator face. The outer scale, called the miles scale, is stationary (Figure 7-10a). The inner circle rotates and is called the minutes scale (Figure 7-10b).

Figure 7-10. Slide rule (calculator) face
The numbers on the computer scale represent multiples of 10, of the values shown. For example, the number 24 on either scale may be 0.24, 2.4, 24, 240, etc. On the inner scale, minutes may be converted to hours by reference to the adjacent hours scale. In Figure 7-10c, for example, 4 hours is found adjacent to 24, meaning 240 minutes.
Relative values must be kept in mind. For example, the numbers 21 and 22 are separated by divisions, each space representing 2 units. Thus, the second division past 21 will be read as 21.4, 214, or 2,140. Between 80 and 90 are 10 divisions, each space representing 1 unit. Thus, the second division past 80 will be read as 8.2, 82 or 820.
There are three index marks on the miles (outer) scale which are used for converting statute miles (SM), nautical miles (NM) and kilometers (KM). The E6-B computer has a scale for converting statute miles, nautical miles, and kilometers. Place the known figure on the inner scale under “naut,” “stat,” or “KM,” as appropriate, and read the equivalent value under the other indexes. For example, to convert 85 statute miles to kilometers and nautical miles, place 85 on the inner scale under the “stat” index. Under the “KM” index, read 137; under the “naut” index read 74.
Each scale has a 10-index used as a reference mark for multiplication and division. The 10-index on the inner scale can also be used as a rate index representing 1 hour. Also on the inner scale is a 60-index, representing 60 minutes and usually used for computation instead of the 10 or 1 hour index (Figure 7-10d) and a 36 or “seconds” index (3,600 seconds = 1 hour) (Figure 7-10e).
The flight computer will commonly be used to solve problems of time, rate, and distance. When two factors are known, the third can be found using the proportion:
Rate (speed) = |
Distance |
Time |
Problem: How far does an aircraft travel in 2 hours and 15 minutes at a ground speed of 138 knots?
Solution: Use the formula distance = ground speed × time
Or use the flight computer in the following manner:

Figure 7-11. Computing distance on the E6-B
Problem: How much time is required to fly 320 NM at a ground speed of 174 knots?
Solution: Use the formula time = distance ÷ ground speed
Or use the flight computer in the following manner:

Figure 7-12. Determining time required on the E6-B
Problem: What is the ground speed if it takes 40 minutes to fly 96 NM?
Solution: Use the formula ground speed = distance ÷ time
Or use the flight computer in the following manner:

Figure 7-13. Determining groundspeed on the E6-B
Problem: If 50 minutes are required to fly 120 NM, how many minutes are required to fly 86 NM at the same rate?
Solution:

Figure 7-14. Determining time-rate-distance on the E6-B
Fuel consumption problems are solved in the same manner as time-rate-distance problems.
Problem: If 18 gallons of fuel are consumed in 1 hour, how much fuel will be used in 2 hours 20 minutes?
Solution:

Figure 7-15. Determining total fuel consumed on the E6-B
Problem: What is the rate of fuel consumption if 30 gallons of fuel are consumed in 111 minutes?
Solution:

Figure 7-16. Determining rate of consumption on the E6-B
Problem: Forty gallons of fuel have been consumed in 135 minutes (2 hours and 15 minutes) flying time. How much longer can the aircraft continue to fly if 25 gallons of available fuel remain and the rate of consumption remains the same?
Solution:

Figure 7-17. Determining flight time remaining on the E6-B
The calculator (slide rule) side of the computer may also be used to determine true airspeed by correcting calibrated airspeed for temperature and pressure altitude. Density altitude is computed simultaneously.
Problem: Using a flight computer and the following conditions, find the true airspeed and the density altitude (DA).
Conditions:
True air temperature: +10°C
Pressure altitude (PA): 10,000 feet
Calibrated airspeed (CAS): 140 knots
Solution:

Figure 7-18. Determining true airspeed and density altitude on the E6-B
The VHF Omnidirectional Range (VOR) is the backbone of the National Airway System, and this radio aid to navigation (NAVAID) provides guidance to pilots operating under visual flight rules as well as those flying instruments.
On Sectional Aeronautical Charts, VOR locations are shown by blue symbols centered in a blue compass rose which is oriented to Magnetic North. A blue identification box adjacent to the VOR symbol lists the name and frequency of the facility, its three-letter identifier and Morse Code equivalent, and other information as appropriate. See the “Radio Aids to Navigation and Communications Box” information in FAA Legend 1.
Some VORs have a voice identification alternating with the Morse code identifier. Absence of the identifier indicates the facility is unreliable or undergoing routine maintenance; in either case, it should not be used for navigation. Some VORs also transmit a T-E-S-T code when undergoing maintenance.
The VOR station continuously transmits navigation signals, providing 360 magnetic courses to or radials from the station. Courses are TO the station and radials are FROM the station.
TACAN, a military system which provides directional guidance, also informs the pilot of the aircraft’s distance from the TACAN Station. When a VOR and a TACAN are co-located, the facility is called a VORTAC. Civil pilots may receive both azimuth and distance information from a VORTAC.
At some VOR sites, additional equipment has been installed to provide pilots with distance information. Such an installation is termed a VOR/DME (for distance measuring equipment).
Flight deck display of VOR information is by means of an indicator as shown in Figure 7-19.

Figure 7-19. The VOR indicator
The omni bearing selector (OBS) is an azimuth dial which can be rotated to select a course or to determine which radial the aircraft is on. The TO/FROM indicator shows whether flying the selected course would take the aircraft to or from the VOR station. A TO indication shows the radial selected is on the far side of the VOR station, while a FROM indication means the aircraft and the selected course are on the same side.
The course deviation indicator (CDI), when centered, indicates the aircraft is on the selected course, or, when not centered, whether that course is to the left or right of the aircraft. For example, Figure 7-20 is indicating that a course of 030° would take the aircraft to the selected station, and to get on that course, the aircraft would have to fly to the left of 030°.

Figure 7-20. Interpreting the OBS and CDI indications
To determine position in relation to one or more VOR stations, first tune and identify the selected station. Next, rotate the OBS until the CDI centers with a FROM indication. The OBS reading is the magnetic course from the VOR station to the aircraft. With reference to Figure 7-21, the line of position is established on the 265° radial of the XYZ VOR.

Figure 7-21. Aircraft on the 265° radial of a VOR
Repeat the procedure using a second VOR. The aircraft is located at the point where the two lines of position cross. See Figure 7-22.

Figure 7-22. VOR orientation using two VORs
To determine the course to be flown to a VOR station on the sectional aeronautical chart, first draw a line from the starting point to the VOR symbol in the center of the compass rose. At the point where the course line crosses the compass rose, read the radial. The course to the station is the reciprocal of that radial. See Figure 7-23.

Figure 7-23. Determining course to a VOR station
The routes established between VORs are depicted by blue-tinted bands showing the airway number following the letter “V,” and are called Victor airways. See Figure 7-24.
When approaching a VOR where airways converge, a pilot must exercise extreme vigilance for other aircraft. In addition, when climbing or descending VFR on an airway, it is considered good operating practice to execute gentle banks left and right for continuous visual scanning of the airspace.

Figure 7-24
VOR receiver accuracy may be checked by means of a VOR Test Facility (VOT), ground check points, or airborne check points.
VOTs transmit only the 360° radial signal. Thus, when the OBS is set to 360°, the CDI will center with a FROM indication; while the reciprocal, 180°, will cause the CDI to center with a TO indication. An accuracy factor of plus or minus 4° is allowed when using a VOT facility.
GPS is a United States satellite-based radio navigational, positioning, and time transfer system operated by the Department of Defense. The system provides highly accurate position and velocity information and precise time on a continuous global basis to an unlimited number of properly equipped users. The GPS constellation of satellites is designed so that a minimum of five are always observable by a user anywhere on earth. The GPS receiver uses data from a minimum of four satellites to yield a three dimensional position (latitude, longitude, and altitude) and time solution.
The GPS receiver verifies the integrity (usability) of the signals received from the GPS satellites through receiver autonomous integrity monitoring (RAIM) to determine if a satellite is providing corrupted information. Without RAIM capability, the pilot has no assurance of the accuracy of the GPS position. If RAIM is not available, another type of navigation and approach system must be used, another destination selected, or the trip delayed until RAIM is predicted to be available on arrival.
Filing a flight plan is not required by regulations; however, it is a good operating practice, since the information contained in the flight plan can be used in search and rescue in the event of an emergency. When completing a flight plan, use the planned cruising altitude in hundreds of feet for the first or the whole portion of the route to be flown expressed as “A” followed by three figures: A075 for 7,500 feet MSL.
Although filing a VFR flight plan is not mandatory (except under certain circumstances), it is considered good operating practice.
The pilot must close a VFR flight plan at the completion of a flight. This can be done by contacting the FAA upon landing.
[10-2024]