# VOR Navigation ## Overview **VOR** stands for **Very High Frequency Omnidirectional Range**. It is a ground-based navigation system that allows pilots to determine their position relative to a station using magnetic radials. VORs are used for: - Enroute navigation - Victor airways - Holding - Instrument approaches - Position fixes - Backup navigation if GPS is unavailable VORs operate in the **108.00 MHz to 117.95 MHz** range. Since VOR signals are VHF, they are generally **line-of-sight**. Reception improves with altitude and can be limited by terrain, distance, aircraft altitude, or service volume. --- ## Basic VOR Concept A VOR station transmits signals in all directions. The aircraft receives those signals and determines which **radial** it is located on. A **radial** is a magnetic course extending **outward from the VOR station**. Examples: - If you are on the **090 radial**, you are east of the station. - If you are on the **180 radial**, you are south of the station. - If you are on the **270 radial**, you are west of the station. - If you are on the **360 radial**, you are north of the station. The biggest thing to remember: > **Radials always go FROM the station.** So if ATC says: > “Proceed inbound on the 090 radial.” That means the aircraft is east of the station, and the course to the station would be approximately **270° TO** the VOR. --- ## How a VOR Works A VOR transmits two signals: - **Reference signal** - **Variable signal** The aircraft compares the phase difference between those signals and determines the aircraft’s magnetic bearing from the station. That bearing corresponds to the radial the aircraft is on. A VOR by itself only provides **course guidance**. It does not provide distance unless it is paired with DME or the aircraft has another approved source of distance information. --- ## VOR Equipment in the Aircraft A basic VOR display usually includes: - **OBS — Omni Bearing Selector** - **CDI — Course Deviation Indicator** - **TO/FROM indicator** - **NAV flag** ### OBS The **OBS** is the knob used to select the desired course. If you want to track a specific radial or course, you rotate the OBS until that course is selected. ### CDI The **CDI** shows whether the selected course is left or right of the aircraft. A simple way to think about it: > **The needle shows where the selected course is.** If the needle is left, the selected course is left of the airplane. If the needle is right, the selected course is right of the airplane. ### TO/FROM Indicator The **TO/FROM indicator** tells you whether the selected course will take you toward or away from the station. - **TO** means the selected course takes you toward the station. - **FROM** means the selected course takes you away from the station. The TO/FROM indication does not tell you which way to turn. It only tells you the relationship between the selected course and the station. ### NAV Flag A **NAV flag** means the signal is unreliable or not being received properly. If the NAV flag is displayed, the indication should not be used for navigation. --- ## Identifying the VOR Before using a VOR, the station needs to be tuned and identified. The only positive way to identify a VOR is by the **Morse code identifier** or the recorded automatic voice identification. Some avionics can decode and display the identifier, but the pilot still needs to verify that the correct station is being used. A good flow is: 1. **Tune** the VOR frequency. 2. **Identify** the station. 3. **Set** the desired course. 4. **Verify** the TO/FROM indication. 5. **Navigate.** Do not just tune the frequency and assume the station is correct. --- # VOR Navigation ## Tracking Directly To a VOR To fly directly to a VOR: 1. Tune and identify the VOR. 2. Rotate the OBS until the CDI centers with a **TO** indication. 3. Turn to the selected course. 4. Correct for wind to keep the CDI centered. The selected course with a **TO** indication is the magnetic course that should take the aircraft toward the station. --- ## Tracking Outbound From a VOR To track outbound: 1. Tune and identify the VOR. 2. Select the desired outbound radial. 3. Verify a **FROM** indication. 4. Fly the selected course away from the station. 5. Correct for wind to keep the CDI centered. Example: If you want to fly outbound on the **360 radial**, select **360°** on the OBS and verify a **FROM** indication. --- ## Intercepting a Radial To intercept a radial: 1. Tune and identify the VOR. 2. Set the desired radial or course. 3. Determine which side of the course you are on. 4. Turn toward the CDI needle. 5. Use an intercept angle, usually around **20° to 45°**. 6. As the CDI centers, turn onto the selected course. The CDI is not pointing to the station. It is showing where the selected course is located. --- ## Cross-Checking Position With Two VORs Two VORs can be used to determine an approximate position. Basic process: 1. Tune and identify the first VOR. 2. Center the CDI with a **FROM** indication. 3. Note the radial. 4. Tune and identify the second VOR. 5. Center the CDI with a **FROM** indication. 6. Note the second radial. 7. Plot where the two radials intersect. This is called a **VOR cross-fix**. --- ## Using VORs on Airways Victor airways are low-altitude airways that are commonly based on VOR navigation. When flying a Victor airway, you may be: - Tracking outbound from one VOR - Tracking inbound to another VOR - Flying a published course between fixes The important part is understanding the difference between a **course** and a **radial**. > **Airways are courses. Radials are always FROM the station.** A course printed on a chart may not always be the same number as the radial you are tracking, depending on whether you are flying to or from the VOR. --- ## VOR Approaches A VOR approach is a **non-precision approach**. It provides lateral guidance, but normally does not provide vertical glidepath guidance. On a VOR approach, the pilot needs to: - Tune and identify the correct VOR. - Set the published inbound course. - Verify the correct TO/FROM indication. - Follow the published procedure. - Comply with all altitude restrictions. - Identify step-down fixes if required. - Descend no lower than the MDA unless the required visual references are in sight. - Identify the missed approach point. - Fly the published missed approach if required. Some VOR approaches may require DME, radar, or another method to identify fixes. If DME is required, the aircraft must have an approved way to provide that distance. --- # Important VOR Concepts ## Radials Are Always FROM the Station A radial is always named for the direction it extends **from** the VOR. Example: If the aircraft is west of the VOR, it is on the **270 radial**. If the pilot wants to fly inbound to the station from the west, the aircraft would fly approximately **090° TO** the station. --- ## Course vs. Radial A **course** is the direction you intend to fly. A **radial** is a magnetic line extending outward from the VOR. Example: - Flying **inbound on the 270 radial** means you are west of the station and flying roughly **090° TO** the station. - Flying **outbound on the 270 radial** means you are flying roughly **270° FROM** the station. Same radial, different direction of flight. --- ## TO/FROM Does Not Mean Turn Direction The TO/FROM indicator does not tell you which way to turn. It only tells you whether the selected course would take you: - Toward the station - Away from the station The CDI still shows where the selected course is located. --- ## Reverse Sensing Reverse sensing can happen when the wrong course is selected or when the pilot is flying opposite of the selected sensing. The easiest way to avoid confusion is: > **Set the course you actually intend to fly.** If you are flying inbound, select the inbound course. If you are flying outbound, select the outbound radial. --- ## Station Passage As the aircraft passes over the VOR, the CDI may become unstable and the TO/FROM indication will switch. This is normal and is called **station passage**. The area directly above the station where indications may become unreliable is commonly called the **cone of confusion**. --- ## Wind Correction A VOR course is not the same thing as a heading. If there is wind, the aircraft may need a wind correction angle to keep the CDI centered. Example: If the selected course is 090° and the wind is pushing the aircraft south of course, the pilot may need to fly a heading slightly north of 090° to maintain the course. The goal is not to keep the heading equal to the OBS setting. The goal is to keep the aircraft tracking the selected course. --- ## VOR Sensitivity VOR course sensitivity is angular. That means the farther the aircraft is from the station, the wider each degree of course deviation becomes. Close to the station, the CDI will react more quickly. Farther from the station, the same CDI movement represents a larger distance from course. This is why VOR tracking usually feels more sensitive near the station and less sensitive farther away. --- # VOR, VOR/DME, and VORTAC ## VOR A standard VOR provides azimuth information only. It gives course guidance but no distance information. ## VOR/DME A VOR/DME provides both: - VOR course guidance - DME distance from the station DME distance is **slant range distance**, not exact horizontal distance. At higher altitudes close to the station, the DME may read higher than the actual horizontal distance because it is measuring the diagonal distance from the aircraft to the station. ## VORTAC A **VORTAC** combines: - VOR azimuth guidance for civilian aircraft - TACAN capability for military aircraft - DME distance information For normal civilian use, a VORTAC can be used like a VOR/DME. --- # VOR Limitations VORs are useful, but they have limitations. Common limitations include: - Line-of-sight reception - Terrain blockage - Range limitations - Service volume limitations - Course roughness - CDI fluctuations - Station passage ambiguity - Need for proper station identification - No distance information unless paired with DME or another distance source VOR reception depends heavily on altitude and distance. A low aircraft far from the station may not receive a reliable signal even if the VOR is operating normally. --- # VOR Checks ## When a VOR Check Is Required Under **14 CFR 91.171**, a VOR equipment check is required before operating under **IFR using VOR navigation**, unless the equipment is maintained, checked, and inspected under an approved procedure. The VOR must have been operationally checked within the preceding **30 days** and found to be within the allowable limits. This applies when using the VOR system for IFR navigation. It is not just a random aircraft inspection item. --- ## Required VOR Check Record The person completing the VOR check must record: - Date - Place - Bearing error - Signature The record may be kept in the aircraft log or another approved record. --- ## VOR Check Methods ### VOT Check A **VOT** is a VOR test facility. To use a VOT: 1. Tune the VOT frequency. 2. Center the CDI. 3. The OBS should read either: - **0° FROM** - **180° TO** Maximum allowable error: **±4°** --- ### Certified Airport Surface Checkpoint Some airports have a designated VOR checkpoint on the airport surface. To use one: 1. Position the aircraft at the published checkpoint. 2. Tune and identify the VOR. 3. Set the published radial or course. 4. Verify the receiver indication. Maximum allowable error: **±4°** --- ### Certified Airborne Checkpoint Some areas have published airborne VOR checkpoints. To use one: 1. Fly over the published checkpoint. 2. Tune and identify the VOR. 3. Check the published radial. 4. Verify the receiver indication. Maximum allowable error: **±6°** --- ### Airway Check If no VOT, surface checkpoint, or airborne checkpoint is available, the pilot may use an established VOR airway. Basic process: 1. Select a VOR radial that lies along the centerline of an established airway. 2. Select a prominent ground point along that radial, preferably more than **20 NM** from the VOR. 3. Fly directly over that point at a reasonably low altitude. 4. Compare the indicated bearing to the published radial. Maximum allowable error: **±6°** --- ### Dual VOR Check If the aircraft has two independent VOR receivers, they may be checked against each other. To do this: 1. Tune both receivers to the same VOR. 2. Identify the station. 3. Center both CDIs. 4. Compare the indicated bearings. Maximum allowable difference between the two receivers: **4°** --- # VOR MON The FAA has been reducing the number of VORs as the National Airspace System moves toward GPS and performance-based navigation. Even with that shift, VORs still matter because they provide a conventional backup if GPS becomes unavailable. The backup network is called the **VOR Minimum Operational Network**, or **VOR MON**. The purpose of the VOR MON is to allow aircraft to continue using conventional navigation during a GPS outage. It allows pilots to navigate VOR-to-VOR or proceed to an airport where an ILS, LOC, or VOR approach can be flown without relying on GPS, DME, ADF, or surveillance. A good way to think about it: > **GPS may be the main tool in modern cockpits, but VORs are still the backup plan when GPS is unavailable.** # References - AIM 1-1-3 — VHF Omnidirectional Range - AIM 1-1-4 — VOR Receiver Checks - 14 CFR 91.171 — VOR Equipment Check for IFR Operations - FAA VOR MON Program