Updated October 2026
A VOR, short for VHF omnidirectional range, is a ground radio station in the 108.00 to 117.95 MHz band that sends out 360 radials, one for each degree of magnetic bearing from the station. Your receiver works out which radial you are on, and a CDI or HSI shows whether you are left or right of the course you selected.
GPS does most of the navigating now, and the FAA is thinning the VOR network rather than closing it. So the VOR is still on the written, still on the instrument checkride and still on the approach charts at Van Nuys. Here is how the signal works, how to read radials and the flag, CDI versus HSI, what DME adds, and which stations we tune from our ramp.
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What A VOR Is And How The Signal Works
A VOR station transmits two signals at once. One is the same in every direction. The other varies with direction around the station, so the difference between the two tells your receiver the magnetic bearing from the station to you. That bearing is your radial. The receiver does not know which way the airplane is pointing, and that one fact explains most of the confusion students have with the instrument.
The signal travels by line of sight, so range grows with altitude. A station behind a ridge can be unusable on the ramp and solid at 4,500 feet, which matters in a valley ringed by the Santa Monica, Santa Susana and San Gabriel mountains.
Identify every station before you use it. The AIM says the only positive method of identifying a VOR is its Morse code identifier. During maintenance the identifier may be removed, or the station may send T-E-S-T, and either is a warning that the signal may be unreliable. Course alignment is generally within plus or minus 1 degree. Some propeller RPM settings can make the needle wander as much as 6 degrees either way, and a small change in RPM usually settles it.
Radials, TO/FROM And Reverse Sensing
A radial always points away from the station. The 090 radial runs due east, magnetic, so an airplane east of the station flying toward it is on the 090 radial with a course of 270. Getting that backwards is the classic written-test trap.
The omni bearing selector, the OBS, picks a course. The needle shows how far you are from that course, and the flag says whether the course would take you TO the station or FROM it. Fly past the station and the flag flips. Directly overhead there is a short area of confusion where the needle swings and the flag may drop out, and the flag change is how you confirm station passage.
Reverse sensing comes from setting a course that disagrees with your heading. Depart Van Nuys outbound on the 340 radial with 160 still set from the inbound leg, and the flag reads TO while you fly away. The needle now points away from the course, and every correction you make by following it takes you further off. The rule that prevents it: set the course you are actually flying, so the head of the OBS roughly matches your heading.
The needle measures degrees, not miles. At 60 nautical miles from the station, one degree is about a mile off course. At 6 miles it is about a tenth of a mile, which is why the needle becomes so lively close in. The Instrument Rating ACS asks you to track a course with no more than three-quarter-scale deflection on the CDI.
CDI Vs HSI: Reading Each Instrument
The CDI, or course deviation indicator, is the older and simpler instrument: a vertical needle, an OBS knob turning a course card, and a TO/FROM flag. Its card does not move with the airplane, so you have to combine the needle with your heading indicator in your head.
HSI stands for horizontal situation indicator. It puts the course needle on top of the heading indicator, on a card that turns as the airplane turns. You see a little airplane, the compass rose under it, the course pointer you set and the deviation bar offset to one side, a plan view of where you are in relation to the course. Set the course pointer to the course you want and the deviation bar reads correctly on any heading, so the VOR reverse-sensing trap goes away. On a localizer back course, setting the front course on an HSI does the same.
| CDI | HSI | |
|---|---|---|
| What it combines | Course needle, OBS and TO/FROM flag only | Heading indicator plus course pointer and deviation bar |
| Course card | Fixed; turned by hand with the OBS | Rotates with the airplane's heading |
| Reverse sensing | Possible if the course set disagrees with your heading | Avoided when the course pointer is set to the course flown |
| Mental work | You merge needle and heading yourself | The picture is drawn for you |
| Where you will see it | Many older trainers, and as a backup | Glass panels such as the Cirrus Perspective PFD |
We think every student should be able to fly both. The HSI is easier and it is what you will meet in most modern airplanes, but the CDI teaches you to hold the picture yourself, and that is the skill that survives a failed display.
DME, VORTAC And TACAN
DME, distance measuring equipment, adds the second half of a position fix. The airplane sends a pulse, the ground station answers, and the box times the round trip. Under AIM 1-1-7 it works in the 960 to 1215 MHz band and gives reliable signals out to 199 nautical miles at line-of-sight altitude. It is accurate to better than half a mile or 3 percent of the distance, whichever is greater.
DME reads slant range, the straight line from the airplane to the station, not distance over the ground. The error is largest close in and high up. Directly over a station at 6,000 feet above it, the DME shows about 1 nautical mile even though you are over the antenna, because 6,000 feet is almost exactly a nautical mile.
The names on the chart tell you what each station offers. A VOR/DME is a VOR with civil DME. TACAN is a military UHF system that gives azimuth and distance. A VORTAC puts a VOR and a TACAN on one site, so you get VOR azimuth plus the TACAN's distance, and the AIM treats it as one navigation aid.
DME matters on the checkride, where the Instrument Rating ACS asks you to fly a DME arc within 1 nautical mile. It matters in the flight levels too. Under 14 CFR 91.205(e), at and above FL240, any airplane that needs VOR equipment also needs DME or a suitable RNAV system. Our Cirrus SR22 Turbo, N422SN, flies to FL250, so that rule is not academic on our ramp.
VOR Service Volumes And The Minimum Operational Network
Every VOR has a standard service volume, the airspace in which the FAA expects its signal to be usable. AIM 1-1-8 defines the classes. Alongside the older Terminal, Low and High classes, it now lists VOR Low and VOR High volumes with a wider radius above 5,000 feet.
| Class | Altitude Above The Station | Radius |
|---|---|---|
| T, Terminal | 1,000 to 12,000 ft | 25 NM |
| L, Low | 1,000 to 18,000 ft | 40 NM |
| H, High | 1,000 to 14,500 ft; 14,500 to 60,000 ft; 18,000 to 45,000 ft | 40 NM; 100 NM; 130 NM |
| VL, VOR Low | 1,000 to below 5,000 ft; 5,000 to below 18,000 ft | 40 NM; 70 NM |
| VH, VOR High | 1,000 to below 5,000 ft; 5,000 to below 14,500 ft; 14,500 to 60,000 ft; 18,000 to 45,000 ft | 40 NM; 70 NM; 100 NM; 130 NM |
The VOR Minimum Operational Network, the MON, is the FAA's plan for a smaller network kept as a backup if GPS becomes unavailable. Under AIM 1-1-3 it is meant to give nearly continuous VOR coverage at 5,000 feet above the ground and to keep a MON airport within 100 nautical miles of any aircraft in the contiguous states. In the western mountains, which the AIM treats separately, nearly all VORs are being kept. Fewer stations elsewhere, but a network that is meant to stay.
VOR Checks For IFR: 30-Day, VOT, Ground, Airborne And Dual
VFR pilots have no VOR check rule. IFR pilots do. Under 14 CFR 91.171 you may use a VOR for IFR only if it was checked within the preceding 30 days and found within the limits below. The exception is equipment maintained under an approved procedure.
| Method | Maximum Bearing Error | How It Works |
|---|---|---|
| Test signal, such as a VOT | Plus or minus 4 degrees | A test signal at the departure airport from an FAA or approved source, or a rated repair station |
| Surface checkpoint | Plus or minus 4 degrees | Taxi to a designated point on the airport and compare the published radial |
| Airborne checkpoint | Plus or minus 6 degrees | Fly over a designated checkpoint, when no test signal or surface point exists |
| Ground point on an airway | Plus or minus 6 degrees | Fly over a prominent landmark on an airway centerline, preferably more than 20 NM from the VOR |
| Dual system check | 4 degrees between the two | Tune both independent receivers to the same VOR and compare |
On a VOT, AIM 1-1-4 says a centered needle should show 0 degrees FROM or 180 degrees TO, whatever you think your position is. Whoever does the check records the date, place and bearing error and signs the aircraft log or other record, as 91.171(d) requires. Expect an examiner to ask for that entry on instrument checkride morning, alongside the transponder and static system inspections. VOTs and checkpoints are listed in the Chart Supplement for each airport.
Tracking A Radial From Van Nuys: The VNY And LAX VORs In Practice
Van Nuys has its own VOR/DME on the field, identifier VNY, and the FAA's October 2026 data put several more within reach. The LAX VORTAC is about 17 nautical miles away, with Van Nuys on roughly its 335 radial. The Santa Monica VOR/DME is about 12 miles, with us near its 337 radial, and its 132 radial is the centerline of the LAX Special Flight Rules Area under 14 CFR 93.95. Fillmore VORTAC sits about 21 miles west.
A first VOR lesson from here is simple. Climb out toward the Simi Valley practice area, tune and identify VNY, center the needle with a FROM flag and fly that radial outbound. Watch how much correction the day's wind asks for. Then turn around, set the reciprocal with a TO flag and intercept it inbound. Add a cross-bearing from Fillmore and you have a fix without GPS, the way pilots found intersections for decades.
The approach charts make the same case. At Van Nuys the October 2026 procedures include a VOR-A and a VOR-B, both circling approaches, and nearby Camarillo, Oxnard and Whiteman each publish a VOR procedure too. We teach the intercepts first in the Redbird MCX full-motion simulator, $120 an hour inside a package, where an instructor can freeze the picture and ask you where you are. A single $189 session is the cheapest way to try it.
GPS Vs VOR: Why You Still Learn It
Most flights from our ramp navigate by GPS, and the Garmin 430 in the Diamond DA20s, the Arrow and the Seminole is a GPS and a VOR receiver in one box. That is exactly why the VOR stays in the syllabus: if GPS is lost, the same box can still show you a radial, as long as you know what to do with it.
The FAA tests it on purpose. The private pilot ACS has a task on navigation systems and radar services. The Instrument Rating ACS, FAA-S-ACS-8C, has Task V.A, intercepting and tracking navigational systems and DME arcs, flown to three-quarter-scale needle deflection, headings within 5 degrees and arcs within 1 nautical mile. A pilot who understands radials also understands GPS courses faster, because the CDI on a GPS approach reads the same way.
If you are earning the private certificate, the VOR is a few lessons inside our private pilot course. If you already hold it, radials, arcs and VOR approaches are core work in our instrument rating, $11,700 with 20 hours in the airplane and 20 in the Redbird MCX.
Related Reading
- Instrument flying skills, the scan, approach charts and holds, one at a time.
- Instrument approach types, from VOR and localizer approaches to ILS and LPV.
- Holding patterns, including how to time a hold at a VOR.
- Instrument rating in Los Angeles, the course, the price and the marine layer.
- Pilotage and dead reckoning, the navigation you fall back on when the radios go quiet.
VOR Navigation FAQ
What Does VOR Stand For In Aviation?
VOR stands for VHF omnidirectional range. It is a ground station between 108.00 and 117.95 MHz that sends out 360 magnetic radials, and the only positive way to identify one is its Morse code identifier.
What Is The Difference Between A CDI And An HSI?
A CDI is a course needle on a fixed card that you turn with the OBS. An HSI lays the course needle over a heading indicator that rotates with the airplane, so it shows your position relative to the course and removes VOR reverse sensing when the course is set correctly.
What Does HSI Stand For?
HSI stands for horizontal situation indicator. Glass panels such as the Cirrus Perspective draw one on the primary flight display, where it shows VOR, localizer and GPS courses on the same compass rose.
What Is DME And How Accurate Is It?
DME is distance measuring equipment. It times a pulse to the ground station and back and shows slant range, accurate to better than half a mile or 3 percent of the distance, whichever is greater, under AIM 1-1-7.
What Is A VORTAC?
A VORTAC is a VOR and a military TACAN on one site. Civil pilots use the VOR for azimuth and the TACAN's distance as DME. The Los Angeles VORTAC is one, about 17 nautical miles from Van Nuys.
How Often Does A VOR Need To Be Checked For IFR?
Within the preceding 30 days, under 14 CFR 91.171. A test signal or surface checkpoint allows 4 degrees of error, an airborne check 6 degrees, and a dual check 4 degrees between receivers, with the date, place, error and signature recorded.
Are VORs Being Shut Down?
Some are. The FAA is reducing the network to a Minimum Operational Network with nearly continuous coverage at 5,000 feet above the ground and a MON airport within 100 nautical miles. Nearly all VORs in the western mountains are being kept.
Track Your First Radial Over The San Fernando Valley
Radials make sense the first time you watch the needle center over a real road. A 60-minute discovery flight from Van Nuys is $229 in a Piper Warrior, you fly it from the left seat, and it is credited in full toward training if you enroll within 24 hours. Already a pilot and thinking about the instrument rating? Book a free consultation and bring your logbook.
Book A Discovery Flight — $229 Book A Free Consultation Call (818) 330-1318
