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RB = BTS – MH
you can find what the needle will
indicate when you get there.
Electricity & Radio 131
Time to Station
As with the VOR, note the seconds
taken to go through a number of
degrees on the relative bearing, and
divide the time just noted by the
number of degrees gone through to
get the time in minutes.
Then use groundspeed (or TAS in
emergency) to find your distance.
Tracking
To find an intercept heading, just
add or subtract the intercept angle to
the track you wish to establish, as
with an airway. It’s common to use
90° inbound and 45° outbound, but
use whatever ATC and
circumstances (or exam questions)
dictate (30° is nice). Note the track,
and add or subtract your heading, as
appropriate, to get the expected
relative bearing when on track,
which you will be when the needle
of a fixed card points to it. With an
RMI, just watch the needle.
When drifting, the needle will always
point to the side of the aircraft the
wind is coming from, so corrections
inbound should always be made that
way, ensuring that the needle actually
goes to the other side of the
longitudinal axis once a corrected
heading is established. For example,
if you want to track 090°, and the
wind is coming from the right, to be
on track you want to end up in a
situation where the heading is an
equal amount of degrees the other
side of the lubber line as the needle
is, such as a heading of 110° (plus 20
of the lubber line), looking for a
340° relative bearing (minus 20 of
the lubber line).
Or, to use another example, for a
track of 090°, your heading might be
070° while the ADF needle points to
110° (heading minus 20°, looking for
plus 20° from the needle). If you are
going the same way as your track,
the needle will tell you which way to
go. If it is on the left, your track will
be on the left, and vice versa. Just turn
whichever way until the needle reads
the desired intercept on the opposite
side. A good ploy is to allow the drift
to happen until you get a positive
reading, say 10° port, double it the
other way (20° starboard), and when
you are back on track, reduce by half
(i.e. 10° in this case) to hold it.
When tracking outbound, however,
you want to end up with the needle
on the same side as the wind, so,
although you are still looking for the
plus 20, minus 20 equation, the
needle would be pointing at 160°
RB. When you make your initial
turn, the needle looks like it's going
the wrong way, but it's something
you get used to.
In short, if the pointy end of the
needle moves to the right of a line
between 0° and 180°, fly right, as
drift is to the left, and vice versa.
DME
Distance Measuring Equipment is also
UHF-based, between 962 and 1213
MHz. It is actually secondary radar,
which measures the time difference
between paired pulses being sent
from the aircraft, and being received
back on different frequencies, 63
MHz away (there are 126 DME
channels). In other words, the
aircraft is the first to transmit on
UHF, then the DME transmitter
returns the signal, plus 63 MHz.
Two frequencies are used because,
otherwise, the first pulse received
would be the ground return from
132 Canadian Private Pilot Studies
below the aircraft. Similarly, the
ground station could self-trigger
from other sources, such as those
being bounced off a building. Jittering
is used on the PRF so the DME's
own pulse can be identified.
Instruments in the cockpit will not
only show your distance to a station,
but will calculate the rate of
movement and display the
groundspeed (just multiply the
distance flown in 6 minutes by 10 if
yours doesn't). It is normally based
with a VOR or TACAN and has a
range of about 200 nm, ± 6, with an
accuracy better than ½ nm or 3% of
the distance, whichever is the
greater. The reason it's not
completely accurate is because the
distance measured is the slant range
from the station, and not from your
equivalent position on the ground,
although at long distances and lower
altitudes, this will be minimised.
GPS
The Global Positioning System was
originally set up by the US military,
using 24 satellites orbiting every 12
hours to give extreme accuracy at a
very much reduced cost compared
to, say, INS. Although they have
　
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