(Continued from VOR
Navigation : part 2)
TRACKING TO A VOR
One of the most often used procedures with a VOR is tracking.
ATC clear you direct XYZ VOR via 090 radial. Okay, great! We have
a clearance, now how do we get there? Here's the outline of the process:
- Select the proper frequency
- Identify the station using the Morse Code identifier
- Make sure you are receiving a usable signal (no Off flag)
- Select the omni bearing of the desired course.
Once these steps are taken, orient the aircraft with respect to
the desired course. In other words, if you are planning to track
To the VOR on a given course, orient yourself to that heading either
mentally or by turning to that approximate heading. If the aircraft
heading is approximately the same as the desired course, the donut
(center) of the indicator represents the aircraft, and the CDI is
the desired course. To intercept the radial, turn toward the CDI.
An intercept angle of 30° or less is a good one to use provided
you are not too far off course. For greater distances off course,
an intercept in the 60°-90° range may be necessary.
Using the VOR indicator in this manner uses the indicator as a
command instrument, i.e. commanding a turn toward the CDI to get
on course. This only applies when the aircraft heading is in the
same approximate direction as the desired heading.
Once the course is intercepted, you must maintain a heading that
will keep you on the desired course. In a no wind situation, the
MH on the HI (Magnetic Heading on the Heading Indicator) and the
OBS will be the same. Let's look at a graphical example:
Aircraft 1 is on a heading of 060° and has set the desired course
of 030° (R 210) into the OBS. The CDI indicates that the desired
radial is right of the current position. The difference between
the course and the OBS gives an intercept angle of 30°.
The pilot elects to continue on the present course, as indicated
by Aircraft 2. The CDI has started moving toward center, so we know
that we are getting close to the desired course.
In Aircraft 3, the CDI is centered and a left turn to 030° is made.
This puts the aircraft on a course of 030° to the VOR and on the
WIND CORRECTION ANGLE DETERMINATION
If there is a crosswind, a wind correction angle (WCA) will
be required. For example, if you are headed north on a course of
360° and there is a west wind, the aircraft will drift east. A good
rule of thumb to follow in this situation is to double the number
of degrees you are off course and turn that amount toward the desired
course. For example, if you notice a drift to the east of two dots
(4°) you would turn west (left) 8° or a heading of 292°. When you
are again on course, turn right by half of the correction (4°) to
a course of 296°. This process is known as bracketing the course.
Since the wind may change in direction or strength as you continue
along your course, small corrections may be required periodically.
For a wind from the east, just reverse the process. The key to tracking
a VOR course is small corrections before the error becomes too great.
TRACKING FROM A VOR
The process of tracking from a VOR is essentially the same as tracking
To a VOR. The main difference is that the heading and OBS settings
will be the same, rather than the reciprocal as in tracking To the
A complication arises when tracking a VOR and then turning 180°. The
CDI in this situation will not be a command instrument and in order
to get on course, you would steer away from the CDI rather than toward
the CDI. The best course of action in this case is to reset the OBS
so that proper indication is given. For example, if tracking From
the VOR on the 180 radial and then turning to track inbound To the
same VOR, as done in a course reversal or procedure turn, reset the
OBS to 360 after the turn.
INTERCEPTING A COURSE
The key to intercepting a course is visualization. The pilot needs
to ask several questions:
- Where am I?
- Where do I want to go?
- What is the best route to get there?
The easiest method to orient yourself is to center the CDI. This
will occur with two different (reciprocal) headings. Choose the
indication that is closest to the aircraft heading. If the aircraft
is heading toward the VOR, this will be a To indication and if headed
away from the VOR a From indication. This answers the "Where am
Let's assume you have been instructed to track outbound on the
130° radial from XYZ VOR. You are flying a heading of 030° and you
tune in the XYZ VOR. As you turn the OBS, you get a From indication
on 210° and a To indication on the reciprocal, 030°. This tells
you that you are tracking To the VOR on the 210° radial. Now You
know where you are (Aircraft 1). Next, we determine where we want
to go. Since you are heading northeast, you know that the 130° radial
lies to your right, or southeast from the VOR.
To intercept the 130° radial, you would set the OBS to 130° and
make a right turn to 070° for a 60° intercept (Aircraft 2). You
would then maintain a heading of 070° until the CDI starts to move
from a full left deflection toward the center. Just prior to the
CDI centering, you would "lead the turn" by starting your turn to
130° (Aircraft 3). Leading the turn helps prevent overshooting the
desired course and the inefficient procedure of "chasing the needle".
You can calculate the amount of time it will take to make the turn
using a standard rate turn (3° per second). Since you are turning
60°, this would require 20 seconds. When you roll out on 130°, you
should be on course, tracking outbound on the 130° radial.
Intercepting a course to a VOR uses the same process, except you
would set the OBS for the course that gives a To indication, the
reciprocal of the radial you will be tracking inbound. A simple
way to figure reciprocals in your head, since some people have trouble
adding or subtracting 180 is to use an addition and a subtraction.
Either add 200 and subtract 20, or subtract 200 and add 20. Another
way to figure the reciprocal is to visualize the head of the needle
on the course and read the reciprocal under the tail of the needle.
OTHER VOR INDICATORS
The one type of VOR indicator we have not discussed is the RMI (Radio
Magnetic Indicator). This is the type indicator used in the FS98 Lear
45 for VOR 2. The RMI needle always points To the VOR, therefore the
tail of the needle indicates the radial. The RMI when used for a VOR
gives the same indications as when used for ADF or NDB tracking.
There is no OBS since the needle always points to the station. Using
an RMI (Radio Magnetic Indicator) will covered more completely
in the lesson on ADF/NDB.
The HSI, which was briefly discussed earlier has the advantage
of always being a command instrument, since the needle will point
toward the stations and will rotate as the aircraft turns. In other
words, there is no reverse sensing with the HSI.
This concludes Part 3 of the lessons on VOR navigation. We will
cover VOR approaches in later lessons.