User Guide

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RADIO MAGNETIC INDICATOR (RMI)
The RMI is the predecessor of the HSI, but it remains a very
handy instrument to have.
You’ll notice that it looks
very much like the ADF indica-
tor in the 172, except that it
has two needles (one of
which has double parallel
lines, just so you can tell
the two apart). In fact, it is
an ADF indicator, among
other things, but with an
important additional fea-
ture. Originally, old-fash-
ioned ADF indicators had a
fixed background card, with 0
at the top and 180 at the bottom,
so figuring out your actual bearing to
a station required considerable mental arithmetic. Later ones, as in
the Cessna, have a movable card, but it must still be set manually
to correspond with your airplane’s heading, and changed manual-
ly every time you make a turn.
The RMI’s compass card, however, is hooked up to the same
remote slaved gyro system that runs the HSI. Thus, the ADF (sin-
gle) needle not only shows you where the station is relative to the
nose of the airplane; you can also read off bearing to the station
directly under the head of the arrow, or your radial from the sta-
tion directly under the arrow’s tail.
The double-needle arrow does the same thing, but it’s
hooked up to a VOR receiver. You’ll recall that the old-fashioned
ADF indicator could show you which way to head to the station,
but not where you were; the standard VOR indicator shows you
where you are with respect to a ground station, but not which way
you’re headed. The RMI gives you both vital pieces of informa-
tion, regardless of whether you’re using VOR or ADF signals for
guidance.
Some GPS-equipped airplanes have the capability to display
the direction to the next GPS waypoint on the RMI; look for an
appropriately-labeled switch.
In the center of the instrument you see a large arrow called,
appropriately enough, the “course arrow.” This is analogous to the
OBS on a conventional VOR indicator. Like an OBS, it can be set
to the desired course using the knob with the arrow symbol at the
7 o’clock position. You’ll notice that the whole course arrow turns
to indicate the course you’ve set against the degrees on the com-
pass ring. If the airplane turns, the course arrow moves with the
compass ring. Thus, as you look at the instrument, you can see both
the desired course and your present heading in relation to the
miniature airplane portrayed at the center of the dial.
The center section of the course arrow can deflect left and
right, and this is analogous to the left-right CDI needle in a standard
VOR indicator. Next to it, a large arrowhead points forward or
backward; this is the TO/FROM indicator. Inadequate nav signals
are indicated by the orange NAV flag at the top of the instrument.
If you’re right on course, the center of the arrow will be
lined up with its head and tail, and will pass under the little air-
plane. If you’re off, the needle will move to one side or the other,
so you instantly see where you are in relation to where you should
be, as if you were looking down upon the airplane and your
desired course from a great height.
The knob at the 5 o’clock position sets the orange heading
“bug,” the V-shaped index that can move around the outside of
the compass ring. You can use it as a handy reminder of the
heading you should hold - and the autopilot will do the same
thing in its HDG mode. To fly a desired heading, just set the bug,
engage the autopilot, hit HDG, and the airplane will turn to and
hold that heading.
Whether you or the autopilot (in NAV) mode is watching the
course arrow to keep it centered, you’ll often notice that it does-
n’t point straight up and down, but slightly off to one side or the
other. This indicates that you (or the autopilot) are correcting for a
crosswind. The difference between the tip of the course arrow and
your actual heading, indicated under the lubber line at the top of
the instrument, shows your wind drift correction at a glance, so
you see intuitively which way the crosswind is blowing. Are you
starting to realize how cool the HSI is?
Finally, it has one “non-horizontal” mode: when you’ve
tuned the nav receiver to an ILS, you can see a glideslope pointer
at the side of the instrument. Thus, you have the complete navi-
gation picture in one place, simplifying your instrument scan.
Flight Instruction
Flight Instruction