VORs and VORTACs are the two most commonly used navigational
aids. The advantage of the VOR over the NDB is the fact that
it directly supplies an indication of the proper course to reach
the VOR or to track a particular course away from the VOR. The VOR
system is used in enroute navigation as well as being a part of
most precision instrument approaches and many non-precision approaches.
While often confusing at first, once you have mastered the use of
the VOR, you are prepared to fly a precise course regardless of
the wind direction. As a matter of fact, by knowing your TAS
(True Air Speed), ground speed and the WCA (Wind Correction
Angle), you can calculate wind direction and speed.
The information you can obtain from a VOR will also allow you to
calculate your ground speed.
From AIM 1-1-3. VHF OMNIDIRECTIONAL RANGE (VOR)
- VORs operate within the 108.0 to 117.95 MHz frequency band and
have a power output necessary to provide coverage within their
assigned operational service volume. They are subject to line-of-sight
restrictions, and the range varies proportionally to the altitude
of the receiving equipment. The normal service ranges for the
various classes of VORs are given in AIM, VOR/DME/TACAN STANDARD
SERVICE VOLUMES (SSV) paragraph 1-1-8d.
- Most VORs are equipped for voice transmission on the VOR frequency.
VORs without voice capability are indicated by the letter "W"
(without voice) included in the class designator (VORW).
- The only positive method of identifying a VOR is by its Morse
Code identification or by the recorded automatic voice identification
which is always indicated by use of the word "VOR" following the
range's name. Reliance on determining the identification of the
omnirange should never by placed on listening to voice transmissions
by the Flight Service Station (FSS) (or approach control facility)
involved. Many FSSs remotely operate several omniranges with different
names. In some cases, none of the VORs have the name of the "parent"
FSS. During periods of maintenance, the facility may radiate a
T E S T code (- . ... -) or the code may be removed.
- Voice identification has been added to numerous VORs. The transmission
consists of a voice announcement, "AIRVILLE VOR" alternating with
the usual Morse Code identification.
- The effectiveness of the VOR depends upon proper use and adjustment
of both ground and airborne equipment.
- Accuracy: The accuracy of course alignment of the VOR is excellent,
being generally plus or minus 1 degree.
- Roughness: On some VORs, minor course roughness may be observed,
evidenced by course needle or brief flag alarm activity (some
receivers are more susceptible to these irregularities than
others). At a few stations, usually in mountainous terrain,
the pilot may occasionally observe a brief course needle oscillation,
similar to the indication of "approaching station." Pilots flying
over unfamiliar routes are cautioned to be on the alert for
these vagaries, and in particular, to use the "to/from" indicator
to determine positive station passage.
- Certain propeller RPM settings or helicopter rotor speeds
can cause the VOR Course Deviation Indicator to fluctuate
as much as plus or minus six degrees. Slight changes to the
RPM setting will normally smooth out this roughness. Pilots
are urged to check for this modulation phenomenon prior to
reporting a VOR station or aircraft equipment for unsatisfactory
1-1-6. VHF OMNIDIRECTIONAL RANGE / TACTICAL AIR NAVIGATION (VORTAC)
- A VORTAC is a facility consisting of two components, VOR and
TACAN, which provides three individual services: VOR azimuth,
TACAN azimuth and TACAN distance (DME) at one site. Although
consisting of more than one component, incorporating more than
one operating frequency, and using more than one antenna system,
a VORTAC is considered to be a unified navigational aid. Both
components of a VORTAC are envisioned as operating simultaneously
and providing the three services at all times.
- Transmitted signals of VOR and TACAN are each identified by
three letter code transmissions and are interlocked so the pilots
using VOR azimuth with TACAN distance can be assured that both
signals being received are definitely from the same ground station.
The frequency channels of the VOR and the TACAN at each VORTAC
facility are "paired" in accordance with a national plan to simplify