12

VOR

The VOR has been largely supplanted by GPS in the real world of IFR, and the FAA has begun decommissioning lesser used VORs across the U.S. The FAA plans to still maintain a minimum operation network of VORs to serve as a backup in the event of a widespread satellite navigation outage.

The VOR is a very high frequency (VHF) NAVAID that is used in instrument flying. Its full name is the very high frequency omni-directional radio range, commonly abbreviated to the VOR, VHF omni range, or omni.

Each VOR ground station transmits on a specific VHF frequency between 108.00 and 117.95 megahertz (MHz), which is immediately below the frequency range used for VHF communications. A separate VHF-NAV radio is required for navigation purposes, but is usually combined with the VHF-COM in a NAV/COM set.

The VOR was developed in the U.S. during the late 1940s and was adopted by the International Civil Aviation Organization (ICAO) as the standard short-range radio navigation aid in 1960. When introduced, it offered an immediate improvement over previously existing aids such as the ADF/NDB combination, most of which operated in lower frequency bands than the VOR and suffered significant limitations such as night effect, mountain reflections and interference from electrical storms.

Principal advantages of the VOR over the NDB include:

• a reduced susceptibility to electrical and atmospheric interference (including thunderstorms);
• the elimination of night effect, since VHF signals are line-of-sight and not reflected by the ionosphere (as are NDB signals in the low and medium frequency band); and
• VOR is more accurate than NDBs.

The reliability and accuracy of VOR signals allow the VOR to be used with confidence in any weather conditions, by day or by night, for purposes such as:

• orientation and position fixing (where am I?);
• tracking to or from a VOR ground station;
• holding (for delaying action or maneuvering); and
• instrument approaches to land.

The Main Use of the VOR is for Tracking

The VOR can be used by a pilot to indicate the desired course and the angular deviation from that course.

For a desired course of MC 015, the pilot would expect to steer a heading of MH 015, plus or minus a wind correction angle (WCA). By selecting an omni bearing of 015 under the course index of the VOR indicator, the pilot can obtain tracking information as shown in figure 12-2.

The VOR cockpit display is not heading sensitive, which means that the display will not change as a result of the airplane changing heading. The case illustrated in figure 12-3 shows the same situation as figure 12-2, except that a wind correction angle (WCA) of 10° right is being used by the pilot to counteract a wind from the right, and so the airplane’s magnetic heading is now MH 025 (rather than the previous MH 015).

Note that:

• the VOR indication depends on the angular deviation of the airplane relative to the selected course;
• it’s the position of the airplane not just angular deviation — heading is not involved; and
• the VOR indication will not change with any heading change of the airplane.

VOR Radials

As its name omni suggests, a VOR ground transmitter radiates signals in all directions. Its most important feature, however, is that the signal in any particular direction differs slightly from its neighbors. These individual directional signals can be thought of as courses or position lines radiating out from the VOR ground station, in much the same way as spokes from the hub of a wheel.

By convention, 360 different tracks away from the VOR are used, each separated from the next by 1°, and each with its direction related to magnetic north. Each of these 360 VOR courses or position lines is called a radial. The 075 radial may be written R-075. A radial is the magnetic bearing outbound from a VOR.

An airplane tracking outbound on the 060 radial will diverge from an airplane tracking outbound on the 090 radial. Conversely, if they both reverse direction and track inbound on the 060 radial (240-TO the VOR) and the 090 radial (270-TO), their tracks will converge.

When a VOR is operating normally, the radials are transmitted to an accuracy of ±2° or better.

How the VOR Works

The VOR ground station should transmit to at least ±2° accuracy.

The VOR ground station transmits two VHF radio signals:

1. the reference phase signal, which is omni-directional (the same in all directions); and

2. the variable phase signal, which rotates uniformly at a rate of 1,800 RPM, with its phase varying at a constant rate throughout the 360°.

The antenna of the VOR airborne receiver picks up the signals, whose phase difference (the difference between the wave peaks) is measured, this difference depending on the bearing of the airplane from the ground station. In this manner, the VOR can determine the magnetic bearing of the airplane from the VOR ground station.

The two signals transmitted by the VOR ground station are:

• in-phase on magnetic north, which is the reference for VOR signals;
• 90° out of phase at magnetic east 090°M;
• 180° out of phase at magnetic south 180°M;
• 270° out of phase at magnetic west 270°M; and
• 360° out of phase (back in-phase) at magnetic north 360°M, or 000°M.

Every 10 seconds or so a Morse code identifier signal (or ident) is transmitted, modulated at 1,020 Hz, allowing the pilot to positively identify the VOR. The coded identifier for the Redmond VOR is RDM (dit-dah-dit dah-dit-dit dah-dah). Any associated DME will have a coded identifier broadcast about every 30 seconds, modulated at 1,350 Hz, about one DME ident at a higher pitch tone for every three or four VOR idents.

Some VORs may also carry a message such as a relevant ATIS, hazardous inflight weather advisory service (HIWAS), or automated weather observing system (AWOS).

Some VORs may also carry voice transmissions either identifying them (for example,“Linden VOR,” alternating with the coded identifier), or carrying a message such as a relevant automatic terminal information service (ATIS), HIWAS, or AWOS.

The voice identifier of the VOR must have the word VOR or VORTAC stated after its name for the VOR to be considered identified.

If the VOR ground station is undergoing maintenance, the coded identifier is not transmitted, but it is possible that navigation signals will still be received. Sometimes a coded test signal (dah dit dit-dit-dit dah) is transmitted. Do not use these aids for navigation. No NAVAID signal should be used until positive identification is made.

VOR Distance

The VOR is a very high frequency aid operating in the frequency band 108.0 to 117.95 MHz. It allows high quality “line-of-sight” reception because there is relatively little interference from atmospheric noise in this band. Reception may be affected by the terrain surrounding the ground station, the height of the VOR beacon, the altitude of the airplane and its distance from the station.

The approximate maximum range of a VHF signal is given by the formula (which is printed here for your convenience):

Example 12-1

Different VORs may operate on the same frequency, but they will be well separated geographically so that there is no interference between their VHF line-of-sight signals. The higher the airplane’s altitude, however, the greater the possibility of interference.

Standard Service Volumes

There are prescribed standard service volumes for three classes of VORs (High Altitude — H, Low Altitude — L, and Terminal — T) which define the reception limits usable at various altitudes. The transmitting power of each VOR is designed to achieve its specified volume.

Use standard service volumes when planning routes that are not on Federal airways.

Use standard service volumes when planning an off-airway route (off-airway routes must be flown only in radar contact, and when in radar contact standard service volumes can be exceeded). Standard service volume limitations do not apply to published IFR routes or procedures. For example, if planning an off-airway flight 17,000 feet above the level of a high altitude VOR ground station, the signal is officially usable out to 100 NM. For complete VOR coverage along the route, the H-class VOR ground stations should be within 200 NM of each other, so that their signals overlap and the airplane will always be within range (100 NM at that altitude) of a VOR.

The class of a VOR is specified in the Chart Supplement U.S., along with any restrictions on its use, such as unreliability between certain radials. Within its Directory Legend, the Chart Supplement U.S. also contains a table of altitudes versus distances. These are related to the standard service volumes and will help you when planning off-airway routes. The class of a VOR, other than H, is also specified in the NAVAID box on FAA en route charts.

Minimum En Route IFR Altitude (MEA)

The MEA is the lowest published altitude between NAVAID fixes that:

• meets obstacle clearance requirements between those fixes; and
• assures acceptable navigational signal coverage between those fixes.

Thus the MEA may be higher than the safe altitude to ensure continuous NAVAID reception.

Minimum Obstruction Clearance Altitude (MOCA)

The MOCA is the lowest published altitude between NAVAID fixes that:

• meets obstacle clearance requirements between those fixes; but
• assures acceptable navigational signal coverage only within 22 NM (25 SM) of a VOR.

Therefore, in certain terrain, the MOCA may provide safe clearance but may not ensure continuous signal coverage. These gaps are depicted on the en route charts. The MOCA may be lower than the MEA, but of course can never be higher. For example, the route between two fixes may be labeled with an MEA of 6,000, and a MOCA of 5,000 (written as “✽5000” on FAA charts and “5000T” on Jeppesen charts).

VOR Changeover Point (COP)

It is usual, when tracking en route from one VOR to another, to select the next VOR when the airplane is approximately halfway between them, unless a designated changeover point is specified on the low altitude chart. Selecting the next VOR at the changeover point will mean the stronger signal is being used.

Certain intersections have a specified minimum reception altitude (MRA) published on charts. This is the minimum altitude at which this intersection can be identified; at altitudes lower than the MRA, navigational coverage is not assured.

VORs on Aeronautical Charts

Most aeronautical charts show the position, frequency and Morse code ident of each VOR ground station. Information on a particular VOR may be found in the Chart Supplement U.S., and any changes in this information will be referred to in NOTAMs (to which a pilot should refer prior to flight). You should take time to read the Directory Legend at the front of the Chart Supplement U.S. regarding Radio Aids to Navigation.

A VOR ground station may be represented in various ways on a chart, the common forms are shown in figure 12-12. Since magnetic north is the reference direction for VOR radials, a magnetic north arrowhead usually emanates from the VOR symbol, with a compass rose heavily marked each 30° and the radials shown in 10° intervals. This is generally adequate for in-flight estimation of an off-airway course to an accuracy of ±2°, however, when flight planning prior to flight, it is advisable to be more accurate than ±2°.

Most routes are published on the en route charts as airways, with the courses marked in degrees magnetic, thereby making it easy for the pilot to plan without having to use a protractor or plotter. If, for some reason, the pilot measures the course referencing true north instead of magnetic north using a protractor, then variation needs to be applied to convert to magnetic (“Variation west, magnetic best” or “East is least, west is best”).

The Victor airways between VORs shown on the low-altitude en route charts are marked at either end with the radial out of that VOR. These radials are not always exact reciprocals of each other, especially on east-west tracks, because:

• great circle routes (which the airways are) cross the north-south meridians of longitude at different angles; and
• magnetic variation (also called declination) changes slightly across the country (and this affects the calculation of the magnetic course, which a radial is, from the true course).

There are two sets of en route charts available — those published by Jeppesen, and those published by the FAA’s Aeronautical Information Service (AIS).

VOR/DME, TACAN and VORTAC

Many VORs are paired with DME. Selection of the VOR on the NAV/COM also selects the paired DME, thereby providing both tracking and distance information.

Most civil VORs have an associated distance measuring equipment (DME), providing both azimuth and distance information, and are known as VOR/DMEs. The VOR operates in the VHF range, but the DME, even though automatically selected along with the VOR selection, operates in the UHF range. The military has developed a different navigation system, called TACAN (Tactical Air Navigation system), which operates in the UHF band, and also provides both azimuth and distance information. It requires special airborne equipment (installed only in military aircraft) for the azimuth information to be received, however civil aircraft can receive the TACAN distance information using the DME. When a TACAN ground station has been integrated with a VOR/DME ground station, the combined facility is known as a VORTAC. The end result for a civil pilot using a VORTAC is the same as using a VOR/DME — both VOR and DME information are available.

On Jeppesen en route charts, a small letter D in the VOR box indicates that DME is also available when the VOR frequency is selected. On FAA en route charts, a (channel) number after the NAVAID three-letter ident (SEA 115 at Seattle), indicates DME is automatically available when the VOR frequency is selected. Underlined NAVAID frequencies on FAA charts means no voice is transmitted.

The VOR Cockpit Instrument

The CDI indicates angular deviation from the selected course.

Each “dot” on the CDI equals 2 degrees course deviation.

A full-scale deflection of the VOR at 5 dots indicates a course deviation of 10 degrees or more.

There are various types of VOR cockpit displays, however they are all reasonably similar in terms of operation. The VOR cockpit display, or VOR indicator, or omni bearing indicator (OBI), displays the omni bearing selected by the pilot on the course card using the omni bearing selector (OBS), a small knob that is geared to the card. The omni bearing selector is also known as the course selector.

If the airplane is on the selected radial, then the VOR needle, known as the course deviation indicator (CDI), is centered. If the airplane is not on the selected course, then the CDI will not be centered.

Whether the selected course would take the airplane to or from the VOR ground station is indicated by the TO/FROM flag, removing any ambiguity.

The VOR is only to be used for navigation if:

• the red OFF warning flag is hidden from view;
• the correct Morse code or voice ident is heard; and
• the CDI is not moving erratically.

The red OFF flag showing indicates that the signal strength received is not adequate to operate the airborne VOR equipment, which may be the case if the airplane is too far from the VOR ground facility, too low for line-of-sight reception, or directly overhead where there is no signal. Also, it will show OFF if the equipment is switched off.

Course Deviation

Deviation “dots” on the CDI match up with the 1-in-60 rule: 1 NM off-course in 60 NM = 1° course error, therefore 2° NM off-course in 60 NM = 2° course error, or 1 dot on the VOR.

The course deviation indicator (or CDI) in the VOR cockpit instrument indicates off-course deviation in terms of angular deviation from the selected course. At all times, the reference when using the VOR is the selected course under the course index. (This is a totally different principle to that of the ADF needle which simply points at an NDB ground station and indicates its relative bearing.)

The amount of angular deviation from the selected course is referred to in terms of dots, there being 5 dots either side of the central position. The inner dot on both sides is often represented by a circle passing through them. Each dot is equivalent to 2 degrees course deviation.

• If the airplane is on the selected course, the CDI is centered.
• If the airplane is 2° off the selected course, the CDI is displaced 1 dot from the center (on the circumference of the inner circle).
• If the airplane is 4° off the selected course, the CDI is displaced 2 dots.
• If the airplane is 10° or more off the selected course, the CDI is fully deflected at 5 dots.

Since the CDI indicates angular deviation, the actual distance off-course for a given CDI indication will be smaller the closer the airplane is to the ground station. In a manner of speaking, airplanes tracking inbound are funneled in toward the VOR ground station.

At 1 NM distance from the VOR ground facility, a one-dot deviation from the selected course is a lateral deviation of approximately 200 feet, so:

• at 1 NM, one dot on the VOR indicator = 200 feet laterally;
• at 2 NM, one dot on the VOR indicator = 2 × 200 = 400 feet;
• at 30 NM, one dot on the VOR indicator = 30 × 200 = 6,000 feet = 1 NM;
• at 60 NM, one dot on the VOR indicator = 60 × 200 = 12,000 feet = 2 NM.

TO or FROM

The 090 radial, which is a magnetic bearing of 090 away from the station, is the same position line as 270 to the station. If an airplane is on this position line, then the CDI will be centered when either 090 or 270 is selected with the OBS. Any ambiguity in the pilot’s mind regarding the position of the airplane relative to the VOR ground station is resolved with the TO/FROM indicator.

The TO or FROM flags or arrows indicate to the pilot whether the selected omni bearing will take the airplane to the VOR ground station, or away from it. In the case shown in figure 12-16, the pilot can center the CDI by selecting either 090 or 270 (which are reciprocals) with the OBS. A course of 090 would take the airplane from the VOR, whereas a course of 270 would lead it to the VOR.

Note. In this manual, the active direction is indicated by the white arrow, triangle.

Example 12-2

Figure 12-17 illustrates two indications on the VOR cockpit display informing the pilot that the airplane is on the 235 radial. The 235 radial is either:

• 235-FROM the VOR; or
• 055-TO the VOR.

So, with the CDI centered, the VOR cockpit display could indicate either 235-FROM or 055-TO.

At all times, the reference when using the VOR indicator is the course selected under the course index. The selected course determines CDI deflection and whether the TO or the FROM flag shows.

The VOR Display Is Not Heading Sensitive

The CDI position will not change as the airplane changes heading only as it changes position relative to the selected course.

The VOR indicates the position of the airplane with respect to the selected VOR course, and the actual VOR display in the cockpit will be the same regardless of the airplane’s heading. If the airplane could turn in a circle on-the-spot, the VOR indications would remain the same, and the CDI would not move. Each of the airplanes in figure 12-18 will have the same VOR display, provided the same course is set under the course index with the OBS.

Different Presentations of the Omni Bearing Indicator

There are various presentations of VOR cockpit information. In all cases, full-scale deflection is 10° either side of the selected omni bearing (a total arc of 20°), with five dots either side of center. In many VOR cockpit displays the two inner dots are joined by the circumference of a circle. The dots may be actual dots on some indicators, or they may be tick marks or hash marks.

The CDI may also differ between instruments. On some displays, the whole CDI moves laterally (rectilinear movement); on others, the CDI hinges at the top and swings. Similarly, the means of displaying the selected omni bearing may differ between instruments. It may be shown under a course index, or it may be shown in a window. In some equipment, the TO and the FROM flags may be displayed in the one window, in others they may have separate windows.

In instruments where the VOR cockpit display also doubles as the ILS (instrument landing system) display, which is the usual case, vertical dots may be marked to indicate glide slope deviation (using a second needle which lies horizontal, or is hinged horizontally, so that it can move up or down). When being used for the VOR (and not the ILS), the glide slope needle may be biased out of view, and there may be a red GS warning flag showing.

Preparing the OBI for Use

Prior to using the VOR, a pilot must:

• ensure that the VOR has been checked as suitable for IFR flight (see The VOR Receiver Check below);
• ensure electrical power is available, and switch the NAV/COM on;
• select the desired frequency (as found on the en route charts or in the Chart Supplement U.S.);
• identify the VOR (the coded identifier is specified on the charts); and
• check that the OFF flag is not showing (the signal is usable, otherwise the OFF flag would be visible).

The VOR Receiver Check

It is required that, for a pilot to use the VOR for IFR flight, the VOR equipment of that aircraft either:

• is maintained, checked and inspected under an approved procedure; or
• has been operationally checked within the preceding 30 days as specified below, and is within the limits of the permissible indicated bearing error.

There are five ways in which the VOR receiver may be checked for accuracy prior to IFR flight. The regulations require this check to be logged or for there to be other records, but this doesn’t necessarily need to be carried in the airplane.

1. VOT

Each person making the VOR operational check shall enter the date, place, bearing error, and sign the aircraft log or other record.

FAA VOR test facility, or a radiated test signal from an appropriately rated radio repair station (usually on 108.0 MHz). These are test signals which allow the VOR to be tested for accuracy on the ground. To use the VOT service:

a. Tune the VOT frequency (found in the Chart Supplement U.S. or on the A/G Communications panel of the Enroute Low Altitude Chart). The VOT radiates the 360 radial (360-FROM) in all directions.

b. Center the CDI by turning the OBS; the omni bearing indicator (OBI) should read 360-FROM or 180-TO, with an acceptable accuracy of ±4° (356-FROM to 004-FROM, or 176-TO to 184-TO is acceptable). Should the VOR operate an RMI, its needle should point to 180°±4° with any OBI setting, between 176° and 184° is acceptable.

2. FAA Certified Ground Checkpoint

Pilots may conduct the VOR check required every 30 days.

(Specified in the Chart Supplement U.S.). This is a certified radial that should be received at specific points on the airport surface.

a. Position the airplane on the ground checkpoint at the airport.

b. Tune the VOR and select the designated radial with the OBS. The CDI must be within ±4° of the radial, with the FROM flag showing (since it is a radial), for the accuracy of the VOR receiver to be acceptable.

3. FAA Certified Airborne Checkpoint

(Specified in the Chart Supplement U.S.). This is a certified radial that should be received over specific landmarks while airborne in the immediate vicinity of the airport.

a. Tune the VOR and select the designated radial with the OBS.

b. Visually position the airplane over the landmark, and center the CDI with the OBS. The course reading on the OBI must be within ±6° of the designated radial for the accuracy of the VOR receiver to be acceptable.

4. Dual System VOR Check

If a dual system VOR (units independent of each other except for the antenna) is installed in the aircraft, one system may be checked against the other.

a. Tune both systems to the same VOR ground facility and center the CDI on each indicator using the OBS.

b. The maximum permissible variation between the two indicated bearings is 4°, and this applies to tests carried out both on the ground and in the air.

5. Course Sensitivity Check

This is not a required check.

a. Center the CDI and note the indicated bearing.

b. Turn the OBS until the CDI lies over the last (5th) dot which, ideally, indicates a bearing difference of 10°. Between 10° and 12° is acceptable sensitivity.

Orientation Using the VOR

Orientation

Using the VOR to Obtain a Position Line

Orientation means “to determine an airplane’s approximate position.” The first step in orientation is to establish a position line along which the airplane is known to be at a particular moment.

To obtain a position line using the VOR:

• rotate the OBS until the CDI is centered; and
• note whether the TO or FROM flag is showing.

Example 12-3

A pilot rotates the OBS until the CDI is centered, which occurs with 334 under the course index and the TO flag showing. Illustrate the situation. Could another reading be obtained with the CDI centered?

In this location, the CDI will be centered with either 334-TO or 154-FROM.

Using Two Position Lines to Fix Position

One position line alone does not allow a pilot to positively fix the position of the airplane; it only provides a line somewhere along which the airplane lies. It requires two or more position lines to positively fix the position of an airplane.

To be of any real value for position fixing, the two position lines need to cut, or intersect, at an angle of at least 45°; any cut less than this decreases the accuracy of the fix. Position lines can be provided by any convenient NAVAIDs, including VORs, NDBs and DMEs. Positions defined on charts by this means are known as intersections.

Fixing Position Using Two VORs

Most IFR airplanes are fitted with two independent NAV/COM systems, enabling two different VORs to be tuned at the same time. Two position lines from two different VOR ground stations can then be obtained simultaneously. In an airplane with only one NAV/COM set, a pilot can, if he or she so desires, obtain two position lines using the one NAV/COM by retuning it from one VOR to another — a bit tedious, and an increased workload, but still satisfactory.

Example 12-4

An airplane fitted with two NAV/COMs is tracking MC 134-TO to VOR-A. The pilot obtains these indications:

• VOR 1: VOR-A 115.2 is selected, the tracking VOR, and the CDI centers with 134-TO.
• VOR 2: VOR-B 113.8 is selected, the crossing VOR, and the CDI centers with 220-FROM.

The two VOR position lines intersect at a good angle, and the pilot has a fairly positive indication of where the airplane is. The pilot has a VOR/VOR fix. Often an intersection of two radials from two VORs is used to define a position on the route, and such a position is known as an intersection. These intersections are clearly marked on the en route charts by triangles, with a five-letter name such as CISSI, GLADD, MUSKS, RADEX and ADOBE.

Fixing Position Using a VOR and a DME

A common form of en route position fixing between aids is the VOR/DME fix, based on a ground station where the DME is co-located with the VOR ground station. This is also the case with a VORTAC.

The VOR can provide a straight position line showing the radial that the airplane is on (CDI centered), and the DME can provide a circular position line showing the distance that the airplane is from the ground station. The intersection of the lines is the position of the airplane.

Example 12-5

An airplane tracking north from Squaw Valley (SWR 113.2) has the cockpit indications of SWR VOR 002-FROM, and SWR DME 16 NM. Where is the airplane?

As the en route chart extract in figure 12-23 shows, the airplane is at the TRUCK position, an in-flight position determined purely by NAVAIDs.

Fixing Position Over a VOR

As an airplane approaches a VOR, the CDI will become more and more sensitive as the ±10° funnel either side of course becomes narrower and narrower.

The higher you are flying over the VOR, the wider the cone of confusion and the longer it will take to pass through to regain reliable information.

As the airplane passes through the cone of confusion over the VOR ground station, the CDI may flick from side to side, before settling down again as the airplane moves away from the VOR. The flag will also change from TO to FROM (or vice versa), and the red OFF flag may flicker in and out of view because of the unusable signal. The zone of confusion can extend in an arc of 70° over the station, so it may take a minute or so for the airplane to pass through it before the CDI and the FROM flag settle down, and the OFF flag totally disappears.

VOR station passage is indicated by the first positive complete reversal of the TO/FROM flag.

Fixing Position Passing Abeam a VOR

A common means of checking flight progress is to note the time passing abeam (to one side of) a nearby VOR ground station. The most straightforward procedure is to:

• select and identify the VOR; and
• under the course index, set the radial perpendicular (at 90°) to your course.

Example 12-6

An airplane is tracking MC 350, and will pass approximately 20 nautical miles abeam a VOR ground station out to its right. The VOR radial perpendicular to course is the 260 radial, and so 260 should be set with the OBS.

The CDI will be fully deflected to one side if the airplane is well away from the abeam position, and will gradually move from full deflection one side to full deflection on the other side as the airplane passes through the ±10° arc either side of the selected radial. The airplane is at the abeam position when the CDI is centered.

It is suggested that you set the radial (the bearing from) the off-course VOR on the OBI, in which case the CDI will be on the same side as the VOR until you have passed the radial. In figure 12-25, the VOR is off-course to the right, and before passing abeam the ground station, the CDI will be out to the right. It will center to indicate the abeam position, and then move to the other side.

The abeam position can also be identified by setting the bearing to the VOR under the course index (rather than radial from the VOR), in which case the movement of the CDI will be from the opposite side. It is better practice to standardize on one method, and we suggest setting the radial from.

The 1-in-60 rule, frequently used in navigation, states that 1 NM off-course in 60 NM subtends an angle of 1°. In rough terms, this means that the airplane, as it flies at right angles through the 10° from when the CDI first starts to move to when it is centered, will travel approximately 10 NM abeam the VOR when it is located 60 DME from the VOR ground station (or 5 NM at 30 DME). At say GS 120 knots (2 NM/minute), passing through a 10° arc abeam the VOR will take 5 minutes at 60 DME, or 2.5 minutes at 30 DME.

In a no-wind situation, you can estimate the time it would take to fly directly to the station by measuring the time for a bearing change as you fly abeam the station, and using the simple expression:

Example 12-7

A 10° bearing change abeam a VOR takes 5 minutes. By turning and flying direct to the VOR, the time required to reach the station is:

At a groundspeed of 120 knots (2 NM/minute), this would mean that you are: 2 × 30 = 60 NM from the station.

Crossing a Known Radial from an Off-Course VOR

It is a simple procedure to identify passing a known radial from an off-course VOR and, indeed, many intersections are based on this.

Example 12-8

(Refer to figure 12-28.) LODDI intersection en route on Victor airway V-108 west of Linden VORTAC on the Linden 251 radial, intersecting with the 317 radial of the Manteca VORTAC.

In an airplane fitted with two NAV/COMs, it would be normal procedure to track using NAV-1 on Linden, and check LODDI intersection with NAV-2 on Manteca. Selecting the radial on NAV-2 (rather than the bearing to the VOR), the CDI will be deflected to the same side of the NAV indicator as the VOR ground station until the airplane passes the radial.

With only one NAV/COM, normal procedure would be to leave it on the main tracking aid (Linden) until almost at LODDI intersection (say 3 minutes before ETA), and then select MANTECA VORTAC and the 317 radial. Having identified the LODDI intersection (on crossing this radial), the NAV/COM can then be re-selected to the tracking aid (Linden and later the aid ahead).

If a 1:500,000 sectional chart is being used (rather than an IFR en route chart), you can construct your own checkpoints along the planned course using nearby off-course VORs.

In figure 12-29, the pilot has chosen to check position crossing the 105, 075 and 045 radials from an off-course VOR. By measuring the distance between these planned fixes en route and noting the time of reaching them, the pilot can calculate the groundspeed and revise estimates for positions further along the planned course.

Orientation Without Altering the OBI

It is possible, without altering the omni bearing selector, to determine which quadrant the airplane is in with respect to the selected course.

In figure 12-31, the selected omni bearing is 340.

• The CDI is deflected left, which indicates that, when looking in direction 340, the airplane is out to the right (of the line 340-160); and
• The FROM flag indicates that tracking 340 would take the airplane from the VOR ground station. The airplane is ahead of the line 250-070 when looking in the direction 340.

This puts the airplane in the quadrant:

• away from the CDI; and
• away from the TO/FROM flag.

So it is between the 340 and 070 radials (omni bearings from the VOR ground station). See figure 12-30.

Note. Remember, no information is available from the VOR cockpit display regarding airplane heading. Heading information in degrees magnetic must be obtained from the heading indicator.

Example 12-9

With 085 under the course index, the VOR indicator shows CDI deflected right with the TO flag showing. Position the airplane with respect to the VOR. This method is just a quick means of determining the approximate position of the airplane with respect to the VOR ground station.

Tracking Using the VOR

Tracking to a VOR

To track to a VOR:

• select the VOR frequency;
• identify the station (Morse code ident as shown on the chart, or voice ident with VOR stated after the name);
• check that the red OFF warning flag is not displayed; and
• select the omni bearing of the desired course with the OBS.

Orient the airplane with respect to the desired course, and then take up a suitable intercept heading using the heading indicator (aligned with the magnetic compass). If the airplane is heading approximately in the direction of the desired course, the center circle will represent the airplane, and the CDI the desired course; to intercept course in this case, the pilot would turn toward the CDI.

This is using the VOR indicator as a command instrument, commanding the pilot to turn toward the CDI to regain course. Be aware, however, that this only applies when the airplane’s heading is in roughly the same direction as the selected omni bearing.

On intercepting the course, the pilot should steer a reasonable heading to maintain the course, allowing a suitable wind correction angle to counter any wind effect. Remaining on course is indicated by the CDI remaining centered.

Example 12-10

In figure 12-33, with the desired course 030 set under the course index, the CDI is out to the right.

Since the airplane’s initial heading agrees approximately with the course of 030, the pilot concludes that the course is out to the right of the airplane. The CDI out to the right commands the pilot to turn right to regain track and center the CDI.

The pilot has taken up a heading of MH 050 to intercept a course of 030-TO the VOR, which will give the pilot a 20° intercept. This shallow intercept is satisfactory if the airplane is close to the course.

If the airplane is well away from the course, then a 60° or 90° intercept might be more appropriate. This would be MH 090 or MH 120.

Determining Wind Correction Angle when Tracking on the VOR

When tracking inbound on 360-TO a VOR with 360 set under the course index, MH 360 will allow the airplane to maintain course provided there is no crosswind component. If, however, there is a westerly wind blowing, then the airplane will be blown to the right of course unless a wind correction angle (WCA) is applied and the airplane steered on a heading slightly into wind. This is MH 352 in figure 12-35.

If, on the other hand, there is an easterly wind blowing, the airplane will be blown left of course, unless a wind correction angle is applied and the airplane steered on a heading slightly into wind, such as MH 005 in figure 12-35.

Just how great the WCA needs to be is determined in flight by trial and error (preflight calculations using the flight computer may suggest a starting figure for WCA). If the chosen WCA is not correct, and the airplane gradually departs from course causing the CDI to move from its central position, the heading should be altered to regain the course (CDI centered) and a new magnetic heading flown with an improved estimate of WCA. This process of achieving a suitable WCA by trial and error is known as bracketing.

In the real world the wind frequently changes in both strength and direction, and so the magnetic heading required to maintain course will also change from time to time. This becomes obvious by gradual movements of the CDI away from its central position, which the pilot will notice in regular scan of the navigation instruments, and which the pilot will correct by changes in magnetic heading using the heading indicator.

Tracking From a VOR

To track from a VOR (assuming the VOR has not already been selected and identified):

• select the VOR frequency;
• identify the station (Morse code ident or voice ident);
• check that the red OFF warning flag is not displayed; and
• select the omni bearing of the desired course with the OBS.

Orient the airplane with respect to the course, and then take up a suitable intercept heading using the heading indicator (aligned with the magnetic compass). If the airplane is heading approximately in the direction of the course, the center circle will represent the airplane, and the CDI will represent the course.

To intercept course in this case, the pilot would turn toward the CDI. This is using the CDI as a command instrument, commanding the pilot to turn toward the CDI to regain course. Be aware, however, that this only applies when the heading is roughly in the same direction as the selected omni bearing. On intercepting course, the pilot steers a suitable heading to maintain it, keeping in mind the wind direction and strength. If the course is maintained, the CDI will remain centered.

Example 12-11

In figure 12-36, with the course 140 set with the OBS, the CDI is out to the right. Since the airplane’s initial heading agrees approximately with the course of 140, the pilot concludes that the course is out to the right of the airplane (or, in this case, straight ahead and to the right).

The pilot steers MH 220 to intercept a course of 140-FROM the VOR, which will give an 80° intercept. This is satisfactory if the airplane is well away from the course. If the airplane is close to course, then a 60° or 30° intercept might be more suitable which, in this case, would be MH 200 or MH 170.

Using the CDI as a Command Instrument

With the course set on the OBI, and the airplane headed at least roughly in the same direction as the selected course, the CDI will act as a command instrument. By flying toward the deflected CDI, the pilot can center it, and thereby regain course.

For example:

• tracking 060-TO the VOR, set 060 under the course index;
• tracking 030-FROM the VOR, set 030 under the course index.

A minor complication arises when the airplane is steered on a heading approximating the reciprocal of the course selected on the OBI. Under these circumstances, the CDI is not a command instrument. This situation is called reverse sensing.

Example 12-12

Suppose a pilot has been tracking 140-FROM a VOR, with 140 selected on the OBI and by steering MH 140. The airplane has drifted left of course, and so the CDI will be deflected to the right of center. Examine figure 12-38 — to regain the 140-FROM course, the pilot must turn toward the needle, in this case to the right. Heading and OBI selection are similar, so it is used as a command instrument.

Suppose now that the pilot wants to return to the VOR ground station on the reciprocal course, which is 320-TO the VOR, and so turns through approximately 180° to MH 320 without altering the 140 set under the course index. The VOR indicator, because it is not heading sensitive, indicates exactly as it did before the turn, with the CDI out to the right of center.

To regain course on this reciprocal heading, the pilot would turn, not toward the CDI, but away from it. Turning toward the CDI on this reciprocal heading to the selected course would take the pilot further away from the selected course and the VOR is no longer a command instrument. This inconvenience can be easily removed, and the OBI returned to being a command instrument, by setting the new course under the course index of MC 320, which approximates the heading being flown. The immediate effect will be for the TO flag to appear, replacing the FROM flag, and the CDI to swing across to the other side. The CDI will now be out to the left, and a turn toward it will bring the airplane back toward the selected course. The VOR indicator is once again a command instrument, easier to understand, and easier to fly.

To keep the VOR indicator as a command instrument when flying on a VOR (so that the pilot can regain course by flying toward the CDI), set the OBI to the course to be flown. A good example of this is a procedure turn (teardrop) that is used in some instrument approaches to reverse direction:

• outbound on 160-FROM, where the pilot should set 160 with the OBS; and
• inbound on 325-TO, where the pilot should set 325 with the OBS.

The 15° between the 2 minute outbound leg in still air and the inbound leg of the descent allows sufficient arc for a standard-rate turn or less to align the airplane nicely for the final descent inbound to the VOR.

Slow aircraft doing a standard-rate turn have a smaller turning radius than fast aircraft (for which the approach plates are designed), and so may tend to undershoot the inbound track (unless there is a strong tailwind in the turn). To avoid undershooting the inbound leg, the airplane should be rolled out of the standard-rate base turn to a suitable heading to allow for a reasonable intercept of the inbound leg (say a 60°, 45° or 30° intercept).

A lot depends on the actual wind strength and direction at the time. For instance, a strong tailwind during the turn will cause the airplane to intercept the inbound leg more quickly than in no-wind or headwind conditions.

Note. The ILS uses the same cockpit instrument as the VOR. Whereas the pilot can select any VOR course, there is only one ILS course. The main points to consider are:

• when flying inbound on the ILS course (known as the localizer), the cockpit display is a command instrument (fly toward the CDI to center it and regain course); but
• when back-tracking from overhead the airport toward the ILS commencement point (flying outbound on the inbound localizer), sensing is reversed and the cockpit indicator is no longer a command instrument.

Intercepting a VOR Course

Visualizing Where You Are and Where You Want To Go

You need to know:

• Where am I?;
• Where do I want to go?; and
• How do I get there?

The easiest method of orienting the airplane using the VOR is to rotate the OBS until the CDI centers. This can occur on one of two headings (reciprocals of each other); choose the one with the omni bearing that most resembles the airplane’s magnetic heading. If the airplane is heading toward the VOR ground station, then the TO flag will show; if it is heading away from the VOR, then the FROM flag will show.

Select the desired course in degrees magnetic with the OBS. Determine which way to turn to intercept the course, then steer a suitable intercept heading.

Intercepting an Outbound Course

The VOR is just as useful tracking away from a VOR ground station as tracking toward it, and it is much easier to use than the NDB/ADF combination.

Example 12-13

An airplane is tracking inbound on the 170 radial to a VOR (350-TO). ATC instructs the pilot to take up a heading to intercept the 090 radial outbound (090-FROM).

Orientation is not a problem in this example since the pilot already knows where he or she is (the usual situation). The better method tracking inbound on the 170 radial is to have 350 set under the course index, since the airplane is tracking 350-TO the VOR. This ensures that the VOR indicator is a command instrument (fly toward the CDI needle to regain course). The pilot visualizes the situation:

• tracking northward toward the VOR;
• the course, 090-FROM, lying ahead to the right.

To intercept the 090-FROM course, the pilot:

• sets 090 under the course index;
• takes up a suitable intercept heading (MH 030 for a 60° intercept); and
• maintains MH 030 until the CDI moves from full-scale deflection toward the center. Depending on your distance from the station, the needle will move at different rates. With experience, you will “lead” the needle by reducing the intercept angle as the needle closes to center.

Intercepting an Inbound Course

Example 12-14

ATC instructs a pilot to track inbound on the 010 radial to a particular VOR. The pilot:

• selects and identifies the VOR; then
• orients himself with respect to the VOR (perhaps by centering the CDI suitably);
• sets the desired course under the course index; inbound on the 010 radial, 190-TO; and determines the relative position of this course;
• takes up a suitable intercept heading, and waits for the CDI to center.

In figure 12-41:

• the CDI centers on 050-FROM (it would also center on 230-TO);
• the pilot has chosen a 90° intercept, steering MH 280 to intercept 190-TO; and as the CDI starts to move (within 10° of the selected course), the pilot leads in to smoothly join course, and allows a wind correction angle of 5° to counter a wind from the east.

Other VOR Presentations

There are various presentations of the VOR cockpit indicator with which a pilot should be familiar. In some aircraft, it is also possible to use an RMI needle to point to the VOR ground station as if it were an NDB. (The tail of the RMI needle shows the radial the airplane is on.) This can, on occasions, be quite useful.

The Radio Magnetic Indicator (RMI)

The radio magnetic indicator (RMI) combines a remote indicating compass and a relative bearing indicator into the one instrument. The RMI is a remote indicating compass with one or two ADF/VOR needles, but without a CDI.

The RMI compass card is continually being aligned so that it indicates magnetic heading, and the RMI needles point at the ground stations to which they are tuned. These ground stations, on many RMIs, may be either an NDB or a VOR, the selection of either ADF or VOR being made with small switches at the base of the RMI.

In figure 12-42, the pilot has selected RMI needle 1 to the ADF, hence:

• the head of needle 1 indicates magnetic bearing to the NDB; and
• the tail of needle 1 indicates magnetic bearing from the NDB.

RMI needle 2 has been selected to the VOR, hence:

• the head of needle 2 indicates magnetic bearing to the VOR; and
• the tail of needle 2 indicates magnetic bearing from the VOR (radial).

Using the RMI with one needle selected to a VOR allows the VOR to be used as if it were an NDB for orientation and tracking purposes.

Orientation with VOR Selected to One Needle on the RMI

This makes orientation with the VOR easy, and it does not involve altering the OBI. In figure 12-43, RMI needle 2 indicates that the magnetic bearing to the VOR is MB 043 (so the airplane is on the 223 radial).

Note that there is no need to alter the OBI to determine this, as would be necessary if an RMI were not installed. Without an RMI, the pilot would have had to alter the OBI until the CDI centered at either 043-TO or 223-FROM.

Intercepting a Course with the RMI Selected to a VOR

If the pilot wishes to intercept the 090 inbound course to the VOR, then he or she would (since the pilot has already oriented the airplane using the RMI):

• set 090 under the course index with the OBS (already done); and
• take up a suitable intercept heading.

If the pilot is uncertain of orientation, he or she can use the ADF technique of imagining (figure 12-44):

• the airplane on the tail of the needle in its current situation; and
• the airplane on the tail of the needle where he or she wants to go (090-TO).

On MH 010, it would be an 80° intercept. If the pilot wanted a 60° intercept, he or she would turn to MH 030. Tracking on MH 030, the RMI needle will gradually fall toward 090. Once the airplane is within 10° of the selected course on the VOR cockpit display, the CDI will start to move.

At this stage, the pilot could shift attention to the VOR indicator, and turn in to track on 090-TO. In this case, the pilot is tracking in on 090-TO, allowing a wind correction angle of 5° left to counteract the wind from the north by steering MH 085.

The Horizontal Situation Indicator (HSI)

The HSI is essentially a heading indicator with a VOR indicator superimposed on it. In addition, this is often a remote indicating compass slaved to a magnetic compass. It provides an easily understood pictorial display and is one of the most popular navigation instruments ever devised. It shows the magnetic heading and the position of the airplane relative to the selected course. In figure 12-45, the left-hand, traditional HSI shows the airplane on MH 175, about to intercept 205-TO the VOR; the right-hand, glass-cockpit HSI shows the airplane on MH 287 about to intercept 013-TO the VOR.

An outstanding benefit of the HSI over the traditional VOR indicator is that the HSI is always a command instrument. Another benefit of the HSI is that it combines two instruments a pilot will need into one single display. The pilot is able to gain more information about the attitude of the aircraft and its flight path while incorporating less instruments in the instrument scan. If the airplane turns, the heading indicating compass card turns, carrying the VOR display with it; therefore the HSI will always show the pilot a CDI deflection toward the selected course. In figure 12-45 in the left-hand image, the selected course is out to the left. If the airplane turns 180° to MH 355, the HSI will show the selected course 205 out to the right of the airplane, which it actually is. In figure 12-45 in the right-hand image, the selected course is out to the right. If the airplane turns 180° to MH 107, the HSI will show the selected course 013 out to the left of the airplane, which it actually is.When using a properly tuned HSI, reverse sensing can be avoided.

The VOR Instrument Approach

When executing a VOR approach, such as that published for Casa Grande (figure 12-47), the VOR is used as the tracking aid. Of course the VOR must be identified before you may use it for navigation. The coded ident for the Stanfield VORTAC near Casa Grande, on which the instrument approach is based, is TFD (dah dit-dit-dah-dit dah-dit-dit).

The top part of the instrument approach chart is a plan view for tracking and the bottom part of the chart is a profile view for vertical navigation.

You may track to the VORTAC at a safe altitude well above the minimum safe altitude (MSA), which is 4,200 feet MSL to the north and 5,600 feet MSL to the south and west. Note the high terrain (4,373 feet MSL) southwest of the airfield at approximately 12 DME TFD. The airport elevation is 1,462 feet MSL and the runway 5 touchdown zone elevation (TDZE) is 1,456 feet MSL. The airport elevation is always higher than the TDZEs since it is the highest point on any of the runways.

When overhead the VORTAC, you must enter the holding pattern based on the TFD VORTAC as the holding fix, holding southwest on the 228 radial, one minute inbound legs. The inbound holding course is 048-TO the VORTAC. Have 048 selected on the OBI and keep the CDI centered when tracking inbound. You may descend to not below 3,500 feet MSL in the holding pattern.

When ready to start the approach, commence the prelanding checks, and adopt an appropriate approach configuration (flaps/gear). You may fly inbound 048-TO the VORTAC not below 3,500 feet MSL and, once past the VORTAC (indicated by the first complete reversal of the flag from TO to FROM), you should start the stopwatch and commence descent. Overhead the VORTAC is the final approach fix (FAF) for this approach (✠).With 048 still set on the OBI, and FROM showing, you should fly a heading that keeps the CDI centered.

DME is available at Casa Grande, however it is not mandatory for this VOR approach. If it were, the approach would be published as a VOR/DME approach. Starting the stopwatch as you pass the VORTAC allows you to determine the position of the missed approach point (MAP) if the DME is not available to begin with, or if it fails while you are completing the approach. The table at the bottom right indicates that if your groundspeed is 90 knots then you will reach the MAP 5 minutes 12 seconds after passing over the VORTAC, which is the FAF. At GS 120 knots, it will take only 3 minutes 54 seconds.

You must not descend below the minimum descent altitude (MDA) 1,960 feet MSL until you are visual. The MDA 1,960 for a straight-in approach is 504 feet above the runway 5 touchdown zone elevation (TDZE) of 1,456 feet MSL (HAT 504 feet).

If you fly out of the clouds during the approach and are visual at the MDA, then at 6.4 DME (noted on the chart as a visual descent point, VDP) a normal descent to the runway 5 touchdown point may be commenced, provided you can see the approach end of the runway and wish to make a straight-in landing.

You should plan your descent from the final approach fix overhead the VORTAC to be at the MDA at or before the visual descent point if you want to make an unhurried and stable normal descent to land straight-in on runway 5. This means descending 1,540 feet (3,500 - 1,960) in 6.4 NM, which means a profile of (1,540 feet 6.4 NM = 241 feet per NM) approximately 250 feet per NM. At a groundspeed of 60 knots this would require a rate of descent of 250 fpm; at a GS of 120 knots it would be 500 fpm; and at GS 90 knots, rate of descent would be 375 fpm. Descending to the MDA at or above these descent rates should position you well.

If you wish to circle to land, then the minimum altitude for this maneuver is also 1,960 feet MSL, the ½ SM visibility required for a straight-in landing is increased to 1 SM for a circling approach to land on runway 23. This is logical because you will have to maneuver away from the runway a little to position for the landing on Rwy 23. The circling MDA 1,960 feet MSL is 498 feet above the airport elevation, 1,462 feet MSL (the highest point on any of the runways), and is 498 feet HAA. (Height above touchdown zone (HAT), is not shown for circling minimums because you might circle-to-land on either runway.)

If you are not visual at the MDA, then you may track in at the MDA in IFR conditions to the missed approach point (MAP) at 7.8 DME, or until the appropriate time has expired. If you become visual at the MDA, you may maneuver to land straight-in or to circle, depending on how you see the situation; otherwise commence a missed approach at the MAP. The missed approach is shown by a dotted line, and detailed on the profile diagram.

Review 12

VOR

1. What does VOR stand for?

2. What frequency does the VOR operate on?

3. What are many VORs coupled with?

4. An airplane at 3,000 feet MSL should be able to receive a VOR situated at sea level out to what range?

5. What is a VOR radial?

6. You are instructed by ATC to track outbound on the 070 radial from a VOR. What is the most suitable heading?

7. You are instructed to track inbound on the 050 radial. What is the most suitable heading?

8. How is a particular VOR identified?

9. What accuracy (±°) should a VOR ground station transmit to?

10. What radio set is used to select a VOR?

11. What is the needle in the VOR cockpit display known as?

12. Any one of 360 tracks may be selected on the VOR cockpit display using what?

13. Where can the position of the VOR receiver checkpoint(s) be found?

14. How many degrees displacement from the selected course are indicated by the following deviations of the CDI on the VOR cockpit display:

a. A 1 dot deviation?

b. A 2 dot deviation?

c. A 3 dot deviation?

d. A 4 dot deviation?

e. A 5 dot deviation?

15. If the CDI is centered with 090 set on the OBI, and the FROM flag is showing, what radial is the airplane on?

16. If the CDI is centred with 090 set on the OBI, and the TO flag is showing, what radial is the airplane on?

17. If the CDI is 2 dots right with 090 set on the OBI, and the TO flag is showing, what radial is the airplane on?

18. If the CDI is 1 dot left with 090 set on the OBI, and the FROM flag is showing, what radial is the airplane on?

19. You are flying MH 080, with the OBI selected to 080, CDI needle showing 2 dots right, and the FROM flag showing. Desired course is the 080 radial outbound. Is the desired course out to your left or right?

20. You are flying MH 300, with the OBI selected to 300, the CDI needle showing 3 dots left, and the TO flag showing. Desired course is 300°M to the VOR. Is the desired course out to your left or right?

21. You are flying MH 300, with the OBI selected to 300, the CDI needle showing 3 dots left, and the TO flag showing. If the airplane is now turned to the reciprocal heading of MH 120, would the indications in the VOR cockpit display change in any way (assuming the OBI is left unaltered)?

22. Refer to figure 12-48. Specify which of the airplanes on the left could have the VOR indications given on the right.

23. Refer to figure 12-49. When checking a dual VOR system by use of a VOT, which illustration indicates that the VORs are satisfactory?

24. Refer to figure 12-50. Which is an acceptable operational check of dual VORs using one system against the other?

25. When making an airborne VOR check, what is the maximum allowable tolerance between the two indicators of a dual VOR system (units independent of each other except the antenna)?

26. You are completing a VOR receiver check with the airplane located on the designated checkpoint on the airport. What do you set on the OBI? How many degrees of the radial must the CDI be within? What should the flag show?

27. The Chart Supplement U.S. specifies an airborne checkpoint as overhead Lafayette (Louisiana) Regional Airport rotating beacon at altitude 1,000 feet, azimuth and distance from LFT VORTAC 340°/25 NM. What are the acceptable VOR indications to meet the requirements for an airborne receiver check of ±6°?

28. Where can the VOT frequency for a particular airport can be found?

29. When testing your two VOR receivers using a VOT, are readings of 176-TO and 003-FROM acceptable?

30. Describe two ways in which a VOR can be positively identified.

31. Should a pilot use a VOR for navigation if that VOR cannot be identified?

32. If a VOR is undergoing maintenance, is its identification removed? Will it still transmit navigation signals?

33. How often is a VOR identification signal transmitted?

34. If a single coded identification from a VORTAC is received only once approximately every 30 seconds, can the VOR be used for navigation? Can the DME be used for navigation?

35. For an airplane flying at the MOCA, for what distance from the VOR is acceptable navigational signal coverage assured?

36. A particular intersection is defined by intersecting radials from two different VORs and is labeled with MRA 6,000. How many NAV/COM sets do you require to identify when you are at the intersection. What is the significance of “MRA 6000?”

37. A 10° bearing change abeam a VOR takes 4 minutes and 30 seconds. If you turn and fly to the VOR, how long will it take, and what is the approximate distance (assume GS 180 knots)?

38. What angular deviation does full-scale deflection of the CDI represent?

39. At 17,000 feet above the level of a H-class VORTAC in the contiguous United States, what will its range be?

40. To use two H-class VORTACs to define a direct route off an established airway at 17,000 feet, how far apart should they be situated?

41. VOR station passage is indicated by:

a. the first full-scale deflection of the CDI.

b. the first movement of the CDI as the airplane enters the zone of confusion.

c. the moment the TO/FROM indicator becomes blank.

d. the first positive, complete reversal of the TO/FROM indicator.

42. To check the sensitivity of a VOR receiver, changing the OBI to move the CDI from the center to the last dot on either side should cause what bearing change?

43. What angular deviation from a VOR course is represented by a half-scale deviation of a CDI?

44. At 60 NM, a half-scale deflection of the CDI with a VOR tuned represents what distance from the course centerline?

45. At 30 NM, a half-scale deflection of the CDI with a VOR tuned represents what distance from the course centerline?

46. If the VOR shows a three dot deflection at 30 NM from the station, how far is the airplane displaced from the radial?

47. After overflying a VOR ground station, you select the desired radial and fly a heading estimated to keep you on that course. What is indicated if there is a steady half-scale deflection of the CDI as you fly some miles away from the station?

48. What does an RMI combine the functions of?

49. What does the HSI combine the functions of?

50. Refer to figure 12-51. In which direction is the aircraft located in relation to the VOR-TAC?

51. Refer to figure 12-52.

a. What is the No. 1 NAV?

b. What is the No. 2 NAV?

c. What is the lateral displacement from the course selected on NAV-1?

d. No. 1 NAV indicates that the aircraft is on which radial?

e. Which OBI selection on the No. 1 NAV would center the CDI and change the ambiguity indication to a TO?

f. What is the angular displacement from the desired radial on the No. 2 NAV?

g. Which OBI selection on the No. 2 NAV would center the CDI?

h. Which OBI selection on the No. 2 NAV would center the CDI and change the ambiguity indication to a TO?

Refer to figures 12-53 and 12-54 for questions 52 to 57.

52. HSI presentation D corresponds to aircraft position:

a. 4.

b. 5.

c. 15.

d. 17.

53. HSI presentation E corresponds to aircraft position:

a. 5.

b. 6.

c. 15.

d. 17.

54. HSI presentation F corresponds to aircraft position:

a. 2.

b. 10.

c. 14.

d. 16.

55. HSI presentation A corresponds to aircraft position:

a. 1.

b. 8.

c. 11.

d. 18.

56. HSI presentation B corresponds to aircraft position:

a. 3.

b. 9.

c. 13.

d. 19.

57. HSI presentation C corresponds to aircraft position:

a. 6.

b. 7.

c. 12.

d. 20.

The VOR Instrument Approach

Refer to figure 12-55 for questions 58 to 64.

58. You are flying to Shelbyville from the South. You are asked by ATC to fly direct to SYI, and then you are cleared for the VOR 18 approach. Explain what you should do after crossing the VOR station.

59. The outbound portion of the approach and procedure turn must take place within 10 nautical miles of the SYI VOR. Why is this so important?

60. What is the minimum altitude that a pilot can execute the procedure turn when flying the VOR 18 approach at SYI?

61. Traditionally, the pilot will switch the OBS from the outbound to the inbound course when they are flying the procedure turn. Why is this a good practice?

62. Although DME can be used on this approach it is not required (DME would only be required if it appeared in the title of the approach, ie VOR/DME RWY 18). Without DME how will the pilot know when they have arrived at the Missed Approach Point?

63. This VOR approach lists the runway number in the title of this approach (VOR RWY 18) but from the airport sketch you can see that this approach is not lined up exactly with the runway centerline. Can you determine from the airport sketch why this VOR is not exactly lined up?

64. The missed approach instructions for the VOR RWY 18 approach at SYI direct the pilot to make a climbing right turn while simultaneously entering the depicted holding pattern. What, if anything, should the pilot do with the OBS setting during the missed approach procedure?