VOR navigation

Name the position and the intended path separately

A VOR supplies azimuth information: the direction of the airplane from the ground station. A radial is a line extending outward from that station, normally referenced to its magnetic orientation. An airplane east of the station is on the 090° radial whether its nose points north, east, south, or west. The receiver does not use the airplane’s heading to determine that radial.

A course is the direction of the path you intend to follow. On the 090° radial, an outbound course is 090°; the inbound course along the same line is its reciprocal, 270°. Add or subtract 180° to find the reciprocal, keeping the result within 001°–360°. “Intercept the 090 radial inbound” therefore calls for the 270° inbound course, not an eastbound heading of 090°.

Heading is where the nose points; track is the actual path across the ground. Wind can require a heading different from the selected course while the airplane remains on that course. Keep these four ideas distinct: radial, selected course, heading, and track. VOR information alone gives a line of position, not distance along that line. A second appropriate bearing, DME, or another suitable position source is needed to establish a fix.

IFH 9-11–9-14: VOR components and orientation

Combine selected course, CDI, TO/FROM, and validity

The omnibearing selector (OBS) sets the course at the index. The course deviation indicator (CDI) shows displacement from the selected line. A centered needle can mean you are on that course’s radial or its reciprocal; the TO/FROM indication distinguishes the two sides of the station. TO means that flying the selected course along the line would take you toward the station; FROM means it would take you away. It does not report the direction the airplane is actually flying.

At either selection, turning the nose while holding the same position does not change the underlying VOR information. An HSI rotates the presentation with heading, but the radial, selected-course relationship, and TO/FROM meaning remain the same. A NAV flag, blank indication, or the installed system’s invalid-data annunciation removes the basis for navigating by that needle. A centered invalid needle is not a usable course.

A typical VOR display reaches full-scale lateral deflection at approximately 10° from the selected course, with five 2° intervals on each side. Confirm the actual indicator scale in its manual. The FAA’s IFH errata corrects the older 12° value on printed page 9-11. Angular sensitivity means the same angular error represents a smaller lateral distance close to the station.

IFH 9-11–9-14: OBS, CDI, TO/FROM and flags · IFH errata, July 25, 2013 item 1: VOR full scale is 10°, not 12°

Verify the received signal before using it

Use a current chart, Chart Supplement, and NOTAMs to choose the facility and frequency. Tune the intended receiver and select that receiver as the navigation source on the CDI/HSI. Check the active frequency, rather than assuming an entry in a standby window is in use. Identify the received VOR by its Morse code or recorded automatic voice identification containing “VOR.” A live Flight Service voice transmission is not positive station identification.

Some installed equipment decodes the identifier from the actual received signal. The current AIM permits verification of that decoded identifier without listening to audio. Other equipment merely shows the expected identifier from its database; that label must be checked against the received audio identification. Learn which method your installation uses. A plausible station name next to the needle is not, by itself, proof that the correct signal is being received.

Set the intended course and check TO/FROM, validity, and whether the result agrees with your expected position. For example, if you expect to be east of a station and select 270° inbound, a FROM indication deserves investigation before any intercept turn. During maintenance the identification may be removed or replaced by a test code. Disregard a facility identified as unusable or inoperative by NOTAM even if the cockpit indication looks normal.

AIM 1-1-3: VOR identification, including decoded versus database-only identifiers · AIM 1-1-1: disregard indications from an unusable transmitter · AIM 1-1-11: identifier removal during maintenance

Orient to the course before correcting

For conventional VOR CDI sensing, select the course you intend to follow. When oriented in that direction, a left needle says the selected line is left; a right needle says it is right. An intercept heading crosses toward the line, then a wind-corrected heading maintains it. The needle tells you where the line lies relative to the selected course, not a required bank angle.

Worked example: you are on the 095° radial, slightly south of the 090° radial, and want to fly inbound along the 090° radial. Select 270° and verify TO. Facing west along that course, north is right; the desired line is right of you. The CDI therefore deflects right. An appropriate intercept toward the north side brings you to the line. The intercept-and-tracking lesson develops the heading choice and lead.

If you instead select 090° with FROM while actually trying to travel west, the conventional CDI deflects left. Turning left simply because the needle is left would move you farther south. This is reverse sensing relative to your intended travel. Restore orientation and select the intended inbound course. Do not solve uncertainty with a large turn or repeated OBS changes.

The heading and relative arrangement on an HSI help show the course geometrically. Its course arrow still needs the correct setting and a valid source; the next lesson compares the presentations. Localizer sensing has different rules because its course is fixed by the transmitter, so do not transfer the VOR OBS rule indiscriminately to a localizer.

IFH 9-14–9-16: reverse sensing, tracking and interception

Use the facility within its usable coverage

VOR is a VHF system subject to line-of-sight limits. Low altitude, terrain, obstructions, facility restrictions, and interference can affect reception. “I can hear it” does not guarantee dependable course guidance at the present position and altitude.

The current AIM lists the original Terminal, Low, and High service volumes and newer VL/VH VOR and DL/DH DME volumes. Read the applicable published class and its altitude/range boundaries; there is no single VOR range for every altitude. Service-volume altitude is measured above transmitter height. A collocated VOR and DME can now have different service-volume classes.

A standard service volume primarily protects off-route use, such as a direct course. Published routes and procedures may use approved extended service volumes beyond the standard boundaries. Standard-volume protection also does not eliminate terrain blockage. Check Chart Supplement restrictions and NOTAMs, including procedure-specific restrictions; do not assume either that every direct course is protected or that a published route outside a standard boundary is automatically unusable.

Course roughness may appear as oscillation or brief flags, particularly in some terrain conditions. Report persistent problems with useful position, altitude, facility, and indication information; consult aircraft guidance for possible onboard causes. Maintain control and a reliable navigation alternative while investigating. Treat intermittent indications as a source-quality problem, not an invitation to chase every movement.

AIM 1-1-3: line-of-sight limits and course roughness · AIM 1-1-8: current standard and extended service volumes · AIM 1-1-13: NAVAID performance reports

Verify the check method, tolerance, and record

Section 91.171 applies when a civil aircraft operates IFR using VOR navigation. It permits equipment maintained, checked, and inspected under an approved procedure, or an operational check within the preceding 30 days that meets the specified error limits. A familiar-looking indication during a flight is not a substitute for the required method and record.

At a VOT, a centered indication should be 000°/360° FROM or 180° TO, within tolerance. Tune its published frequency and check any authorized area or altitude; airborne use is restricted to specifically authorized locations. For the ground-point method, use a prominent point on an established airway radial, preferably more than 20 NM from the station, and cross it at a reasonably low, safe altitude.

Dual-check example: two qualifying receivers show bearings 008° and 012° to the same facility. Their 4° difference meets that method’s limit. Readings 008° and 013° differ by 5° and fail; averaging them does not make the check pass. These are invented readings, not calibration instructions.

Record the date, place, bearing error, and signature in the aircraft log or other record. A repair-station test signal also requires the specified repair-station entry certifying the transmitted bearing and date. Verify the record before using the equipment IFR, and correct an excessive error rather than inventing a personal correction to make it acceptable.

14 CFR §91.171(a)–(d): methods, error limits and record · AIM 1-1-4: VOT use and receiver checks

Distinguish station passage from invalid guidance

Close to and over a VOR, the angular geometry and antenna pattern can make the CDI move rapidly or fluctuate in the cone or zone of confusion. Do not chase that needle with abrupt turns. Maintain the appropriate established heading and cross-check for positive TO-to-FROM transition, distance trend if available, and the expected route position. TO/FROM is more useful than one needle twitch for recognizing passage.

After passage, confirm the outbound leg, source, and course required by the clearance or procedure. The inbound course need not equal the next outbound course. If the next leg uses a different station, tune, identify, and orient to that station at the planned changeover rather than merely waiting for an old needle to become unusable.

A flag far from expected passage, missing or wrong identification, a persistent implausible course, or a known outage calls for a failure response. Maintain control using reliable instruments, stop using the suspect guidance, verify source/frequency and available independent evidence, and use the aircraft procedures. Do not assume GPS is automatically an authorized replacement for every VOR-dependent operation. Advise ATC of affected capability and request appropriate assistance. Under §91.187, in-flight navigation-equipment malfunctions while IFR in controlled airspace must be reported as soon as practical.

IFH 9-14–9-16: passage and operating errors · AIM 1-1-3: TO/FROM and roughness · 14 CFR §91.187: in-flight malfunction reports · AIM 1-2-3: limits on suitable RNAV substitution

Explain the indication before planning a turn

Ground exercise: assume an identified, valid VOR signal and an airplane on its 240° radial. Ignore wind and signal errors for the initial position problem. First say the radial aloud: “I am southwest of the station.” Now choose the course for outbound travel: 240° FROM. For inbound travel along the same line, choose 060° TO. A heading of 320° changes neither answer at that fixed position.

1. Draw a station and a southwest radial. Mark arrows for 240° outbound and 060° inbound.
2. Rotate the airplane symbol through three headings while leaving position and OBS unchanged. The underlying CDI/TO-FROM information stays the same.
3. Move the symbol off the line. State which side of the selected course it occupies before interpreting the needle.
4. Add a source-invalid flag. The geometry still describes where you drew the airplane, but the real receiver can no longer establish that position reliably.

Use the navigation trainer to compare position, course selection, and heading if available; the written exercise remains usable without it. The aim is to form a position picture before selecting a correction. Later instruction adds actual wind, intercepts, approved-equipment operation, and flight performance.

IFH 9-11–9-16: orientation and interception · ACS V.A, printed page 12