8
RADIO NAV — CHAPTER 8 · NOTES
VOR
by Ghost Aviator
LECTURE PARTS
Ghost Aviator
www.ghostaviator.com
Ghost Aviator
www.ghostaviator.com
Ghost Aviator
DGCA CPL / ATPL Study Notes • Radio Navigation
✈ Chapter 8: VOR
VHF Omnidirectional Range
📋 Contents
1. Introduction & Background 2. Principle of Operation 3. Terminology — Radials & Bearings 4. Frequencies & Channels 5. Identification & Monitoring 6. Types of VOR 7. Range & Coverage 8. DOC (Designated Operational Coverage) 9. Accuracy & Errors 10. Cone of Confusion 11. Cockpit Displays — CDI, RMI, HSI 12. In-Flight Procedures 13. VOR Summary Table 14. Practice Questions (33 Q)1. Introduction & Background
VOR — VHF Omnidirectional Range — is the primary short-range radio navigation aid used worldwide. It provides magnetic bearing information to/from a ground station and forms the backbone of conventional airway navigation.
Fig 8-1: VOR/DME station with omnidirectional polar diagram
📡 Key Facts
- Adopted by ICAO in 1960 as the standard short-range navaid
- Operates in the VHF band — immune to static interference and skywave
- Provides magnetic bearing to/from the station (azimuth service)
- Emission designator: A9W
- Co-located with DME → VOR/DME; with TACAN → VORTAC
Frequency Band
108.0 – 117.95 MHz
Total Channels
160 channels
Shared with ILS
108.0 – 111.95 MHz (40 ch)
VOR only
112.0 – 117.95 MHz (120 ch)
2. Principle of Operation
The VOR works by phase comparison of two 30 Hz signals. The phase difference between the two signals equals the aircraft's magnetic bearing from the station (radial).
🔄 The Two Signals
| Signal | Name | Modulation | Characteristic |
|---|---|---|---|
| Reference | Omnidirectional reference | FM subcarrier (9960 Hz) | Same phase in ALL directions |
| Variable | Directional / variphase | AM on carrier | Phase varies with azimuth (limàcon pattern) |
The variable signal is created by rotating a limàcon (figure-of-eight) radiation pattern at 30 rev/sec. At magnetic north, both signals are in phase. Moving clockwise, the variable signal phase progressively leads the reference — the phase difference equals the radial.
Fig 8-3: Phase differences at cardinal points (N=0°, E=90°, S=180°, W=270°)
⚡ Exam Tip — Phase = Radial
Phase difference (variable − reference) = Radial (QDR) = Magnetic bearing FROM the VOR.
Example: Aircraft due East → phase difference = 90°
Example: Aircraft due East → phase difference = 90°
Fig 8-4: Radial definition — phase difference equals magnetic bearing FROM station
CVOR vs DVOR Signal Generation
| Feature | CVOR (Conventional) | DVOR (Doppler) |
|---|---|---|
| Reference signal | FM subcarrier (9960 Hz ±480 Hz) | AM on carrier |
| Variable signal | AM on carrier (rotating limàcon CW) | FM via Doppler (simulated ACW rotation) |
| Site error | More susceptible | Less site error — preferred at complex sites |
| Antenna array | Single rotating antenna | Ring of 48 antennas, switched electronically |
3. Terminology — Radials & Bearings
Fig 8-5: Tracking between two VORs and RMI usage
📐 Critical Definitions
| Term | Definition | Note |
|---|---|---|
| Radial | Magnetic bearing FROM the VOR (QDR) | What the VOR transmits |
| QDR | Magnetic bearing FROM station to aircraft | RMI tail |
| QDM | Magnetic heading to fly TO station (no wind) | RMI head |
| QTE | True bearing FROM station | Apply variation at VOR |
⚡ Variation Rule
For VOR bearings, apply variation at the VOR station to convert magnetic to true bearing.
This is opposite to ADF/NDB where variation is applied at the aircraft.
This is opposite to ADF/NDB where variation is applied at the aircraft.
✓ Example
Aircraft on radial 090° from a VOR where local variation = 10°W
QDR = 090°M → QTE = 090° − 10° = 080°T (subtract westerly variation)
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QDR = 090°M → QTE = 090° − 10° = 080°T (subtract westerly variation)
4. Frequencies & Channels
| Band | Range | Channels | Notes |
|---|---|---|---|
| Lower VOR band | 108.000 – 111.975 MHz | 40 channels | Shared with ILS Localiser — even tenths = VOR (108.0, 108.2…); odd tenths = ILS |
| Upper VOR band | 112.000 – 117.975 MHz | 120 channels | VOR exclusive |
⚡ Frequency Sharing (108–112 MHz)
Even tenths (108.0, 108.2, 108.4…) = VOR | Odd tenths (108.1, 108.3…) = ILS Localiser.
This allows 40 VOR + 40 ILS channels in the shared band.
This allows 40 VOR + 40 ILS channels in the shared band.
📡 Emission Designator: A9W
A = Amplitude modulation (DSB full carrier) | 9 = Composite signal | W = Combination (telephony + telegraphy + navigation)
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5. Identification & Monitoring
Station Identification
📻 Ident Methods
- 3-letter Morse code transmitted every 10 seconds on a 1020 Hz subcarrier
- Some stations also broadcast voice ATIS on the VOR frequency
- Keyed at 7 words per minute
Special Beacon Types
| Type | Ident Signal | Purpose | Use? |
|---|---|---|---|
| TST | TST in Morse | Test beacon — under maintenance/calibration | ❌ DO NOT USE |
| VOT | Continuous dots | VOR Test facility — checks aircraft VOR equipment | ✓ Ground test only |
⚠ VOT Test Limits
When checking with a VOT, the aircraft must read 000° ± 4° (FROM) or 180° ± 4° (TO).
Maximum permissible error = ±4°
Maximum permissible error = ±4°
Monitoring
🔍 Automatic Site Monitor
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- Built-in monitor checks VOR bearing accuracy continuously
- If bearing error exceeds ±1° → station shuts down or switches to standby transmitter
- During standby switchover: ident is suppressed for 30 seconds
- Rule: NEVER USE a VOR when no ident is heard
6. Types of VOR
| Type | Full Name | Power | Use |
|---|---|---|---|
| CVOR | Conventional VOR | Standard | En-route navigation |
| DVOR | Doppler VOR | Standard | Sites with terrain/structure interference |
| TVOR | Terminal VOR | Low (≤50W) | Airfields — short range approach/departure |
| VOT | VOR Test facility | Very low | Ground equipment check only |
| VORTAC | VOR + TACAN | Standard | Civil (VOR) + Military (TACAN bearing + DME) |
| VOR/DME | VOR + DME | Standard | Provides bearing + distance |
📡 DVOR — Doppler Mechanism
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- AM carrier = reference signal
- Ring of 48 antennas switched electronically to simulate a rotating antenna
- Doppler effect creates the FM variable signal
- Simulated rotation is anticlockwise (opposite to CVOR) — receiver processes identically
- Less susceptible to multipath site errors than CVOR
7. Range & Coverage
VOR is a line-of-sight (LOS) system. Range depends on aircraft altitude and terrain.
📡 LOS Range Formula
Note: Coefficient 1.25 is used for all DGCA exam calculations (some texts show 1.23, but exam answers verify with 1.25).
Range (NM) = 1.25 × (√Htx + √Hrx)
Where H = height in feet above terrain.Note: Coefficient 1.25 is used for all DGCA exam calculations (some texts show 1.23, but exam answers verify with 1.25).
✓ Example
Aircraft at 10,000 ft, VOR antenna at 100 ft above terrain:
Range = 1.25 × (√10000 + √100) = 1.25 × (100 + 10) = 1.25 × 110 = 137.5 NM
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Range = 1.25 × (√10000 + √100) = 1.25 × (100 + 10) = 1.25 × 110 = 137.5 NM
8. DOC — Designated Operational Coverage
Fig 8-7: DOC diagram showing range/altitude pairs
📐 DOC Definition
- Specifies the range and altitude within which the VOR provides reliable navigation service
- Published as a range/altitude pair — e.g., 50 NM / FL 250
- Means: reliable up to 50 NM from the station at or below FL 250
- Valid day AND night (unlike NDB/ADF which has a day-only DOC)
✓ VOR DOC vs ADF DOC
VOR DOC is valid day and night — VHF is not affected by skywave.
NDB/ADF DOC is day only — MF/LF skywave at night causes bearing errors.
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NDB/ADF DOC is day only — MF/LF skywave at night causes bearing errors.
9. Accuracy & Errors
| Error Source | Value | Notes |
|---|---|---|
| Site/terrain error | ±1° | Multipath reflections; DVOR less susceptible |
| Propagation / scalloping | ±1° | Bending of VHF waves; needle oscillation in affected areas |
| Airborne equipment | ±3° | Receiver and aircraft installation accuracy |
| Total system error | ±5° | ICAO specification (RSS combination) |
⚠ Airway Width — 1:60 Rule
At distance D, lateral error = D × error° / 60.
To maintain ±5 NM half-width with ±5° error: D = (5 × 60) / 5 = 60 NM per leg?
Standard formula for max beacon spacing: max_spacing = 600 / error_degrees
• For ±5° error: 600/5 = 120 NM • For ±5.5° error: 600/5.5 ≈ 109 NM
To maintain ±5 NM half-width with ±5° error: D = (5 × 60) / 5 = 60 NM per leg?
Standard formula for max beacon spacing: max_spacing = 600 / error_degrees
• For ±5° error: 600/5 = 120 NM • For ±5.5° error: 600/5.5 ≈ 109 NM
⚡ Scalloping
Rapid oscillation of VOR bearing indication caused by multipath interference. The CDI needle “scallops” back and forth. More pronounced in mountainous terrain; DVOR is less susceptible.
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10. Cone of Confusion
Fig 8-8: Cone of confusion — unreliable signal area directly overhead the VOR
⚠ Cone of Confusion — Overhead VOR Indications
- OFF flag may appear on CDI/VOR indicator
- TO/FROM indicator alternates rapidly
- CDI needle oscillates / swings
- Extends approximately ±50° from vertical (antenna design dependent)
- Normal and temporary — do not attempt corrections while in the cone
✓ Station Passage Technique
1. Note the moment TO/FROM flag flips to FROM → that is station passage.
2. CDI will settle after exiting the cone (typically within 1–2 minutes at normal speeds).
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2. CDI will settle after exiting the cone (typically within 1–2 minutes at normal speeds).
11. Cockpit Displays — CDI, RMI, HSI
11.1 CDI — Course Deviation Indicator
Fig 8-9: CDI / OBS (Omni Bearing Selector) deviation indicator
Fig 8-10: Left/Right CDI indications for various radial/OBS combinations
Fig 8-11: TO/FROM indications on CDI
📐 CDI Key Facts
| Parameter | Value |
|---|---|
| Sensitivity | 2° per dot |
| Full Scale Deflection (FSD) | ±10° (= ±5 dots) |
| TO indication | QDM is within ±80° of OBS setting |
| FROM indication | QDR is within ±80° of OBS setting |
| OFF indication | OBS is ~90° away from QDM/QDR (ambiguous zone) |
⚡ CDI Sense — Critical Rule
The CDI only shows correct turn direction when the OBS setting matches your actual desired track. If OBS is set wrong, the needle sense can be reversed — this is the classic DGCA CDI trap!
⚠ CDI Worked Example
Aircraft on 152° radial, OBS = 329° (TO). Desired radial = 149°. Aircraft is 3° to the RIGHT of desired track.
Therefore aircraft is to the LEFT of the 329° course → CDI bar deflects RIGHT (fly right).
Deflection = 3° ÷ 2°/dot = 1.5 dots right.
Therefore aircraft is to the LEFT of the 329° course → CDI bar deflects RIGHT (fly right).
Deflection = 3° ÷ 2°/dot = 1.5 dots right.
11.2 RMI — Radio Magnetic Indicator
Fig 8-12: RMI reading example — phase difference to bearing conversion
Fig 8-13: RMI display and geometry
📐 RMI Key Facts
| Needle Part | Reading | Equivalent |
|---|---|---|
| Head (arrowhead) | Points TO the station | QDM — magnetic bearing TO station |
| Tail | Points AWAY from station | QDR — radial — magnetic bearing FROM station |
The RMI compass card rotates with aircraft heading, so the needle always reads magnetic bearings (not relative bearings).
✓ RMI Worked Examples (from page 128 Q1–4)
Q1-4: Four RMI diagrams for worked examples
- Q1: Heading 360°, needle head at 071° → QDM = 071°, QDR = 251°
- Q2: Heading 090°, needle head at 159° → QDM = 159°, QDR = 339°
- Q3: Heading 220°, needle head at 345° → QDM = 345°, QDR = 165°
- Q4: Heading 270°, needle head at 063° → QDM = 063°, QDR = 243°
11.3 HSI — Horizontal Situation Indicator
Fig 8-15: CDI deviation bar within HSI display
Fig 8-17: Full HSI display with course pointer and heading
📐 HSI Key Facts
| Parameter | Standard HSI | Narrow-bar HSI |
|---|---|---|
| Sensitivity | 5° per dot | 2° per dot |
| Dots each side | 2 dots | 2 dots |
| FSD | ±10° | ±4° |
The HSI course pointer rotates with aircraft heading → the deviation bar always shows correct turn direction regardless of OBS setting. No CDI sense reversal.
🔷 CDI vs RMI vs HSI Comparison
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Summary comparison: RMI, CDI, and HSI displays side by side
12. In-Flight Procedures
Fig 8-23: In-flight VOR tracking procedures
Fig 8-24: VOR/DME approach procedure
✓ Outbound Tracking (away from VOR)
- Set OBS to desired outbound radial (e.g., 090° for east outbound)
- FROM flag appears
- Wind correction: CDI drifts right → turn right to correct (normal sense with FROM selected)
✓ Inbound Tracking (toward VOR)
- Set OBS to inbound track (reciprocal of radial, e.g., 270° for inbound on 090° radial)
- TO flag appears
- CDI normal sense — fly toward the needle
📡 Station Passage Indications
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- Primary: TO → FROM flag change
- CDI needle may swing briefly
- OFF flag may appear momentarily in cone of confusion
- Log time of station passage for flight planning
13. VOR Summary Table
Complete VOR Summary Table
| Parameter | Value / Detail |
|---|---|
| Frequency band | 108.0 – 117.95 MHz (VHF) |
| Total channels | 160 (40 shared with ILS + 120 VOR only) |
| Emission designator | A9W |
| Principle | Phase comparison of two 30 Hz signals |
| Ident interval | 3-letter Morse every 10 s (1020 Hz tone) |
| Monitor trigger | ±1° bearing error → auto-shutdown |
| VOT tolerance | ±4° |
| Site error | ±1° |
| Total system accuracy | ±5° |
| DOC validity | Day AND night |
| LOS range formula | 1.25 × (√H1 + √H2) NM (H in feet) |
| CDI sensitivity | 2°/dot, FSD ±10° |
| HSI sensitivity | 5°/dot standard (FSD ±10°); 2°/dot narrow |
| Radial (QDR) | Magnetic bearing FROM VOR to aircraft |
| Variation applied at | VOR station (not aircraft) |
| Cone of confusion | ±50° from vertical — OFF flag, needle oscillates |
14. Practice Questions
⚡ Instructions
Click “Show Answer” to reveal the correct answer and explanation. All questions are DGCA CPL/ATPL standard.
Q1. What is the frequency band used by VOR?
(a) 225–400 MHz
(b) 108–117.95 MHz
(c) 190–1750 kHz
(d) 962–1213 MHz
Answer: (b)
VOR operates in the VHF band, 108.0–117.95 MHz. (a) = UHF military TACAN; (c) = NDB/ADF MF/LF band; (d) = DME UHF.
VOR operates in the VHF band, 108.0–117.95 MHz. (a) = UHF military TACAN; (c) = NDB/ADF MF/LF band; (d) = DME UHF.
Q2. The principle of operation of a VOR is:
(a) Comparison of two 9960 Hz signals
(b) Pulse timing like DME
(c) Phase comparison of two 30 Hz signals
(d) Amplitude comparison of two signals
Answer: (c)
VOR uses phase comparison of two 30 Hz signals. The reference is omnidirectional (FM subcarrier); the variable rotates (AM on carrier). Their phase difference = radial.
VOR uses phase comparison of two 30 Hz signals. The reference is omnidirectional (FM subcarrier); the variable rotates (AM on carrier). Their phase difference = radial.
Q3. A VOR radial is defined as:
(a) Magnetic heading to fly to the station
(b) True bearing from aircraft to station
(c) Magnetic heading of the aircraft
(d) Magnetic bearing FROM the station to the aircraft (QDR)
Answer: (d)
A radial = QDR = magnetic bearing FROM VOR to aircraft. Aircraft on the 090° radial is due east of the station.
A radial = QDR = magnetic bearing FROM VOR to aircraft. Aircraft on the 090° radial is due east of the station.
Q4. A VOR station antenna is at 100 ft; aircraft at 3,600 ft. Using coefficient 1.25, maximum LOS range is:
(a) 87.5 NM
(b) 75 NM
(c) 100 NM
(d) 62.5 NM
Answer: (a)
Range = 1.25 × (√3600 + √100) = 1.25 × (60 + 10) = 1.25 × 70 = 87.5 NM.
Range = 1.25 × (√3600 + √100) = 1.25 × (60 + 10) = 1.25 × 70 = 87.5 NM.
Q5. Which statement about a VOT is correct?
(a) It radiates a continuous tone and is used to check aircraft VOR equipment accuracy on the ground
(b) It is a type of VOR for terminal area use
(c) It stands for ‘VOR on Test’ and should not be used
(d) It provides bearing guidance to the test facility
Answer: (a)
A VOT (VOR Test facility) radiates a continuous Morse dots tone. Used on the ground to verify aircraft VOR receiver accuracy. Aircraft must read 000°(±4°) FROM or 180°(±4°) TO.
A VOT (VOR Test facility) radiates a continuous Morse dots tone. Used on the ground to verify aircraft VOR receiver accuracy. Aircraft must read 000°(±4°) FROM or 180°(±4°) TO.
Q6. Maximum permissible bearing error when checking VOR airborne equipment using a VOT:
(a) ±4°
(b) ±3°
(c) ±5°
(d) ±2°
Answer: (a)
VOT maximum permissible error = ±4°. Exceeding this requires equipment servicing before use.
VOT maximum permissible error = ±4°. Exceeding this requires equipment servicing before use.
Q7. The DOC of a VOR is valid:
(a) During daylight hours only
(b) During night hours only
(c) During twilight periods only
(d) Both day and night
Answer: (d)
VOR DOC is valid day AND night. VHF is immune to skywave propagation. Contrast with NDB/ADF whose DOC is day only.
VOR DOC is valid day AND night. VHF is immune to skywave propagation. Contrast with NDB/ADF whose DOC is day only.
Q8. Total system accuracy of a VOR is:
(a) ±1°
(b) ±3°
(c) ±5°
(d) ±10°
Answer: (c)
Total VOR accuracy = ±5°: site error ±1° + propagation/scalloping ±1° + airborne equipment ±3° (RSS combination).
Total VOR accuracy = ±5°: site error ±1° + propagation/scalloping ±1° + airborne equipment ±3° (RSS combination).
Q9. Flying directly over a VOR station, the indications are:
(a) OFF flag appears, TO/FROM alternates, CDI oscillates (cone of confusion)
(b) TO flag, CDI centres
(c) Bearing becomes more accurate
(d) No change — VOR is accurate overhead
Answer: (a)
Overhead VOR = cone of confusion: OFF flag may appear, TO/FROM alternates rapidly, CDI needle oscillates. Normal and temporary.
Overhead VOR = cone of confusion: OFF flag may appear, TO/FROM alternates rapidly, CDI needle oscillates. Normal and temporary.
Q10. On a standard CDI, angular value of one dot deflection:
(a) 5°
(b) 1°
(c) 2°
(d) 10°
Answer: (c)
CDI sensitivity = 2° per dot. Full scale = 5 dots × 2° = ±10°.
CDI sensitivity = 2° per dot. Full scale = 5 dots × 2° = ±10°.
Q11. Full Scale Deflection on a standard CDI:
(a) ±5°
(b) ±10°
(c) ±20°
(d) ±2°
Answer: (b)
CDI FSD = ±10° (5 dots × 2°/dot).
CDI FSD = ±10° (5 dots × 2°/dot).
Q12. Which RMI statement is correct?
(a) Arrowhead points into the tailwind
(b) Tail indicates QDM
(c) Arrowhead indicates QDM (magnetic bearing TO station)
(d) RMI shows track made good
Answer: (c)
RMI: arrowhead (head) = QDM = bearing TO station. Tail = QDR = radial = bearing FROM station.
RMI: arrowhead (head) = QDM = bearing TO station. Tail = QDR = radial = bearing FROM station.
Q13. Compared to CVOR, a DVOR:
(a) Operates at higher frequencies
(b) Uses a single rotating antenna
(c) Has a larger cone of confusion
(d) Has less site error due to its electronically switched antenna array
Answer: (d)
DVOR uses a ring of 48 antennas switched electronically. Doppler effect generates FM variable signal. Less susceptible to site errors from terrain/structures.
DVOR uses a ring of 48 antennas switched electronically. Doppler effect generates FM variable signal. Less susceptible to site errors from terrain/structures.
Q14. Aircraft on 090° radial from VOR. Station variation = 6°E. The QTE is:
(a) 084°T
(b) 096°T
(c) 090°T
(d) 264°T
Answer: (b)
QDR = 090°M. Apply variation at VOR: 090° + 6° (East) = 096°T. (True = Magnetic + East variation)
QDR = 090°M. Apply variation at VOR: 090° + 6° (East) = 096°T. (True = Magnetic + East variation)
Q15. Max beacon spacing for airway with ±5 NM half-width, VOR error 5°:
(a) 120 NM
(b) 60 NM
(c) 150 NM
(d) 100 NM
Answer: (a)
Max spacing = (half-width × 60) / error = (5 × 60) / 5 × 2 = 600/5 = 120 NM. (Using the standard 600/error_degrees formula.)
Max spacing = (half-width × 60) / error = (5 × 60) / 5 × 2 = 600/5 = 120 NM. (Using the standard 600/error_degrees formula.)
Q16. Max beacon spacing if VOR bearing error is 5.5°:
(a) 120 NM
(b) 100 NM
(c) 109 NM
(d) 80 NM
Answer: (c)
Max spacing = 600 / 5.5 ≈ 109 NM.
Max spacing = 600 / 5.5 ≈ 109 NM.
Q17. Number of VOR channels in the 108–112 MHz band:
(a) 80 total
(b) 160 total
(c) 40 VOR channels (even tenths only)
(d) 20 VOR channels
Answer: (c)
108–112 MHz: even tenths = VOR (40 channels); odd tenths = ILS Localiser (40 channels).
108–112 MHz: even tenths = VOR (40 channels); odd tenths = ILS Localiser (40 channels).
Q18. Total number of VOR channels:
(a) 200
(b) 160
(c) 120
(d) 40
Answer: (b)
Total VOR channels = 40 (shared, 108–112) + 120 (VOR only, 112–118) = 160.
Total VOR channels = 40 (shared, 108–112) + 120 (VOR only, 112–118) = 160.
Q19. Aircraft heading 287°, starboard drift 14°. Track made good (radial being flown):
(a) 273°
(b) 287°
(c) 301°
(d) 315°
Answer: (c)
Track = Heading + Starboard drift = 287° + 14° = 301°. QDR = track when flying outbound from VOR.
Track = Heading + Starboard drift = 287° + 14° = 301°. QDR = track when flying outbound from VOR.
Q20. Aircraft heading 287°, 14° starboard drift. VOR phase difference reading:
(a) 273°
(b) 287°
(c) 301°
(d) 315°
Answer: (c)
Phase difference = radial = QDR = Track = 287° + 14° = 301°.
Phase difference = radial = QDR = Track = 287° + 14° = 301°.
Q21. CDI shows TO indication when:
(a) Aircraft is heading toward the station
(b) Aircraft is closer than 10 NM
(c) QDM is within ±80° of OBS-selected course
(d) Aircraft is below the cone of confusion
Answer: (c)
TO flag illuminates when QDM (bearing to station) is within ±80° of the OBS setting. Not dependent on aircraft heading — geometry only.
TO flag illuminates when QDM (bearing to station) is within ±80° of the OBS setting. Not dependent on aircraft heading — geometry only.
Q22. Aircraft on 152° radial. OBS set to 329° (TO). CDI indication:
(a) Bar deflects RIGHT — approximately 1.5 dots
(b) Bar deflects LEFT — approximately 1.5 dots
(c) Bar centred
(d) OFF flag
Answer: (a)
OBS 329° TO means desired radial = 149°. Aircraft is on 152° — 3° clockwise of 149° → aircraft is LEFT of the 329° inbound course → bar deflects RIGHT (fly right). 3° ÷ 2°/dot = 1.5 dots.
OBS 329° TO means desired radial = 149°. Aircraft is on 152° — 3° clockwise of 149° → aircraft is LEFT of the 329° inbound course → bar deflects RIGHT (fly right). 3° ÷ 2°/dot = 1.5 dots.
Q23. At 100 NM from VOR with ±5° total error, lateral displacement is approximately:
(a) 5 NM
(b) 7.5 NM
(c) 8.3 NM
(d) 8.7 NM
Answer: (d)
Exact: 100 × sin(5°) = 100 × 0.0872 ≈ 8.7 NM. Using 1:60: 100 × 5/60 ≈ 8.3 NM.
Exact: 100 × sin(5°) = 100 × 0.0872 ≈ 8.7 NM. Using 1:60: 100 × 5/60 ≈ 8.3 NM.
Q24. VOR variation should be applied at:
(a) Aircraft position
(b) Mid-point between aircraft and station
(c) The VOR station
(d) The destination aerodrome
Answer: (c)
For VOR, variation is applied at the VOR station. Contrast with NDB/ADF: variation applied at the aircraft.
For VOR, variation is applied at the VOR station. Contrast with NDB/ADF: variation applied at the aircraft.
Q25. Aircraft on 045° radial. RMI shows:
(a) Head at 045°, tail at 225°
(b) Head at 225°, tail at 045°
(c) Head and tail both at 045°
(d) Head at 225°, tail at 225°
Answer: (b)
QDR (radial) = 045° → RMI tail = 045°. RMI head = QDM = 225° (reciprocal). Answer: head 225°, tail 045°.
QDR (radial) = 045° → RMI tail = 045°. RMI head = QDM = 225° (reciprocal). Answer: head 225°, tail 045°.
Q26. Standard HSI CDI is set to 5°/dot. Full scale deflection is:
(a) 5°
(b) 10°
(c) 20°
(d) 15°
Answer: (b)
Standard HSI: 5°/dot × 2 dots = 10° FSD.
Standard HSI: 5°/dot × 2 dots = 10° FSD.
Q27. VOR ident transmission interval:
(a) Every 30 seconds
(b) Every 5 seconds
(c) Every 10 seconds
(d) Every 15 seconds
Answer: (c)
VOR Morse ident is transmitted every 10 seconds.
VOR Morse ident is transmitted every 10 seconds.
Q28. If the VOR auto-monitor detects bearing error >±1°:
(a) Station automatically shuts down or switches to standby, suppressing ident
(b) Transmits a warning tone
(c) Continues at reduced power
(d) Changes frequency
Answer: (a)
Auto-monitor: if error >±1° → station shuts down or switches to standby. Ident suppressed for 30 s. Never use VOR without ident.
Auto-monitor: if error >±1° → station shuts down or switches to standby. Ident suppressed for 30 s. Never use VOR without ident.
Q29. VORTAC provides:
(a) VOR bearing for civil aircraft and TACAN bearing + DME for military aircraft
(b) VOR bearing only
(c) DME for civil and military only
(d) ILS and VOR combined
Answer: (a)
VORTAC: civil aircraft receive VOR azimuth + DME distance (via TACAN DME on paired freq). Military: TACAN bearing + DME.
VORTAC: civil aircraft receive VOR azimuth + DME distance (via TACAN DME on paired freq). Military: TACAN bearing + DME.
Q30. VOR emission designator:
(a) A9W
(b) A2A
(c) N0NA1A
(d) P0N
Answer: (a)
VOR = A9W. A = AM DSB; 9 = composite signal; W = combination of telephony, telegraphy and navigation.
VOR = A9W. A = AM DSB; 9 = composite signal; W = combination of telephony, telegraphy and navigation.
Q31. HSI (5°/dot), aircraft is 4° to the right of selected course. CDI bar:
(a) Right by 2 dots
(b) Left by 2 dots
(c) Left, less than 1 dot
(d) Right, less than 1 dot
Answer: (c)
5°/dot HSI. Aircraft 4° RIGHT of course → bar deflects LEFT (fly left to intercept). Magnitude = 4° ÷ 5°/dot = 0.8 dots left = less than 1 dot LEFT.
5°/dot HSI. Aircraft 4° RIGHT of course → bar deflects LEFT (fly left to intercept). Magnitude = 4° ÷ 5°/dot = 0.8 dots left = less than 1 dot LEFT.
Q32. DVOR differs from CVOR in that:
(a) Different frequencies
(b) Uses Doppler effect with an array of antennas to generate FM variable signal; AM is the reference
(c) Larger DOC
(d) Uses pulse modulation
Answer: (b)
DVOR: AM carrier = reference; electronically switched 48-antenna ring generates FM variable via Doppler effect. CVOR: FM subcarrier = reference; AM rotating limàcon = variable.
DVOR: AM carrier = reference; electronically switched 48-antenna ring generates FM variable via Doppler effect. CVOR: FM subcarrier = reference; AM rotating limàcon = variable.
Q33. Aircraft on radial 270°, heading 090° inbound to VOR, OBS set to 090°. TO/FROM indicator shows:
(a) TO
(b) FROM
(c) OFF
(d) Alternating TO/FROM
Answer: (a)
Aircraft west of VOR flying east (inbound). QDM = 090°. OBS = 090°. QDM is within 80° of OBS → TO.
Aircraft west of VOR flying east (inbound). QDM = 090°. OBS = 090°. QDM is within 80° of OBS → TO.
Annex A — HSI Diagrams (Q31)
Annex A: HSI options for Question 31
Annex B — HSI Diagrams (Q32)
Annex B: HSI options for Question 32
Annex C — HSI Diagrams (Q33)
Annex C: HSI options for Question 33
Additional Question Diagrams
Q3 — RMI Options
Q3: Four-option RMI diagram
Q15 — RMI Options
Q15: Four-option RMI diagram
Q25 (RMI) and Q26 (CDI)
Q25 RMI and Q26 CDI diagrams
Q28 — RMI Options
Q28: Four-option RMI diagram
Q30 — CDI Options
Q30: Four-option CDI diagram
DGCA CPL/ATPL Radio Navigation Study Notes
Chapter 8 — VOR (VHF Omnidirectional Range)
Ghost Aviator | www.ghostaviator.com
For personal study use only. Not to be reproduced without permission.
Chapter 8 — VOR (VHF Omnidirectional Range)
Ghost Aviator | www.ghostaviator.com
For personal study use only. Not to be reproduced without permission.
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