VORTAC – Combined VOR and TACAN Navigation Systems

Overview

VORTAC is a critical, dual-use ground-based radio navigation system that integrates VOR (VHF Omnidirectional Range) and TACAN (Tactical Air Navigation) technologies. Designed for seamless operation by both civil and military aviation, it provides precise azimuth (bearing) and distance (slant range) information from a single location, reducing infrastructure redundancy and supporting interoperable, efficient airspace management worldwide.

VORTAC stations are foundational to the global air navigation structure. They are strategically sited to support overlapping coverage for high-density flight corridors, remote routes, and military operations. Compliant with rigorous ICAO standards, each VORTAC ensures interoperability, reliability, and accuracy, continuously monitored for performance and safety.

VOR (VHF Omnidirectional Range)

VOR is a principal radio navigation aid for civil aviation, operating in the VHF band (108.00–117.95 MHz). Each VOR station transmits two signal phases: a reference (omnidirectional) and a variable (rotating) phase. Aircraft receivers compare these to determine the bearing (radial) from the station.

• Display Instruments: Course Deviation Indicator (CDI), Horizontal Situation Indicator (HSI), or Radio Magnetic Indicator (RMI) provide instant position feedback.
• Classes: Terminal (T), Low (L), and High (H) VORs differ in their service volume (range and altitude).
• Morse Code: Each VOR broadcasts a three-letter identifier pilots must verify before use.
• Limitations: VOR signals are line-of-sight and may be blocked by terrain or structures.

TACAN (Tactical Air Navigation)

TACAN is a UHF-based (962–1215 MHz) navigation system primarily used by military aircraft. It offers both azimuth and distance information, with higher accuracy and resistance to jamming compared to civilian systems.

• Azimuth & DME: Provides magnetic bearing and slant range, with the azimuth accessible only to military receivers.
• Channels: 252 (126 X and 126 Y) allow flexible frequency assignments.
• Deployment: Fixed, mobile, and shipboard installations support rapid, worldwide military operations.
• Civil Access: Civilian aircraft can access DME from TACAN but not bearing, unless co-located with VOR (as in VORTAC).

DME (Distance Measuring Equipment)

DME measures slant range distance by calculating the time delay between aircraft-interrogated pulses and ground station replies.

• Frequency: Operates in UHF (962–1213 MHz).
• Accuracy: ±0.2 NM or 3% of distance, whichever is greater.
• Display: Digital cockpit readouts integrated with NAV receivers.
• Limitations: Slant range error is greatest when overhead; actual distance may overstate ground distance.

VORTAC Ground Station Design

A VORTAC Ground Station combines VOR and TACAN equipment at a single site:

• VOR (VHF): Provides azimuth for civil and military users.
• TACAN (UHF): Adds azimuth (military) and DME (all users).
• Automatic Monitoring: Systems continuously verify signal quality and automatically remove Morse identifiers if out of tolerance.
• Charting: Identified by unique symbols and published frequencies/channels.

How VORTAC Works

1. VOR Component: Transmits reference and variable phase signals; aircraft receivers determine radials.
2. TACAN Component: Provides highly accurate UHF azimuth (military) and shared DME.
3. Frequency Selection: Civil pilots tune the VOR frequency; military pilots select the TACAN channel.
4. Display: Onboard instruments show bearing and distance in real-time for navigation, approaches, and reporting.

System Comparison: VOR, VOR/DME, TACAN, VORTAC

• VORTAC = most versatile: civil pilots get VOR/DME; military get full TACAN.

Civilian vs. Military Use

• Civilian Aircraft: Use VOR for bearing, DME for distance.
• Military Aircraft: Use TACAN for both bearing and distance, with enhanced accuracy and jamming resistance.
• Dual-Use: VORTAC ensures both user groups access required navigation without interference.

Advantages of VORTAC

• Dual Service: One installation serves both civil and military needs.
• Redundancy: If one component fails, the other may remain operational.
• International Standardization: Simplifies charting, training, and interoperability.
• Cost Efficiency: Reduces infrastructure and maintenance overhead.
• High Reliability: Redundant power supplies and continuous monitoring.

Limitations and Cautions

• Line-of-Sight: Terrain and altitude affect signal reception.
• Slant Range Error: DME overstates ground distance when overhead.
• Cone of Confusion: Azimuth unreliable directly above the station.
• No Voice on TACAN: Voice ATIS/FSS only on VOR-equipped stations.
• Interference Risks: High-altitude aircraft may pick up multiple stations on same frequency.
• Identification: Always verify Morse code ID before using for navigation.

Practical Usage and Examples

• Enroute Navigation: Airways defined by VORTAC radials and distances.
• Position Fixing: Cross radials or DME/radial intersection.
• Instrument Approaches: Step-down fixes, missed approach points, and DME arcs.
• Military: Tactical navigation, aerial refueling rendezvous, and formation flying.
• Example: TOBE VORTAC (TBE), Colorado—anchors airways and instrument procedures.

Charts, Symbols, and Frequency Information

• VORTAC Symbol: Hexagon with center dot, box, and dashes.
• Chart Data: Station name, Morse ID, VOR frequency, TACAN channel, latitude/longitude, service class, and voice availability.
• Frequency Pairing: Aircraft NAV receiver auto-selects paired DME channel.

Operational Notes for Pilots

• Verify ID: Do not use any station without matching Morse code.
• Monitor NOTAMs: Outages or maintenance affect station availability.
• Expect Fluctuations: CDI and TO/FROM indicators may fluctuate overhead (cone of confusion).
• DME Lag: DME holds last valid reading briefly after signal loss.
• Reverse Sensing: Set OBS/course correctly to avoid reversed indications.
• Use Published Volumes: Plan navigation within service volume limits.
• Cross-Check: Always cross-check navigation with backup systems when possible.

VHF (Very High Frequency)

• Range: 30–300 MHz; aviation uses 108.00–137.00 MHz.
• VOR Band: 108.00–117.95 MHz, 50 kHz channel spacing.
• Characteristics: Line-of-sight, low atmospheric noise, suitable for navigation and communication.

UHF (Ultra High Frequency)

• Range: 300 MHz–3 GHz; TACAN and DME use 962–1215 MHz.
• Characteristics: Shorter range, less atmospheric noise, better resistance to jamming (military).

Conclusion

VORTAC stands as a cornerstone of modern aviation navigation, offering reliable, standardized, and dual-use solutions for civil and military airspace users worldwide. Its integration streamlines infrastructure, enhances safety, and ensures the precision needed for both routine and tactical operations.

For more information on integrating advanced navigation solutions for your operation, contact us or schedule a demo .

Further Reading

• FAA Aeronautical Information Manual (AIM)
• ICAO Annex 10, Volume I – Radio Navigation Aids
• Jeppesen Chart Legend
• FAA NOTAM Search