User Guide

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Flight Instruction
Flight Instruction
Finally, most ILSs have a couple of marker beacons . These
are very small transmitters that send a short-range signal straight
up to activate both audio tones and colored indicator lights on
your instrument panel. The outer marker is generally about five
miles from the threshold. As you cross over it, you’ll see a blink-
ing blue light in sync with a low-pitched “boop, boop, boop”
tone. The middle marker is about half a mile from the threshold,
and it emits a “dit-daahhh, dit-daahhh” signal in sync with an
amber panel light.
The skills you’ll use to fly an ILS are essentially the same as
those for a VOR, except that now you have to do them in three
dimensions (and quite a bit more precisely). Where, before, you
simply watched the “fly left” or “fly right” indications of the VOR
needle, now you also have to follow the “fly up” and “fly down”
(or, more accurately, “descend shallower” or “descend steeper”)
indications of the glideslope needle. Let’s work our way through
a typical ILS final approach.
Once again, we’re at Podunk - in this case, on the ILS for
runway 09 at Podunk Municipal. Approach control is vectoring us
onto the final approach course from the southwest, and we’re at
an altitude of 1500 feet. Since we’re well to the right of the local-
izer, the needles are telling us “fly left,” and since we’re well
below the glideslope, they’re also telling us “fly up.” We’ll just
continue to hold our assigned heading of 045 degrees and our
assigned altitude of 1500 feet.
Now we’re beginning to intercept the localizer and we’ve
been cleared for the approach. As the localizer needle “unpegs,”
we’ll turn to the inbound heading of 090 degrees, making small
heading corrections as necessary to center the needle and keep it
there. Here, even more importantly than with VOR, it’s vital
to fly
heading, rather than chasing the needle.
At the outer marker, the glideslope is about 1500 feet AGL,
so as we approach the marker the glideslope needle will start
creeping down from its full “fly up” indication. As it nears the cen-
ter, we’ll adjust aircraft configuration and power to start following
it down. Just as it’s important to fly headings, and not chase the
localizer needle, it’s important to establish a stable rate of descent
on the vertical speed indicator, correcting as necessary with small
changes in power and pitch attitude, rather than “chasing the
glideslope.”
As we continue down the approach, the needles will
become more and more sensitive - make your corrections small-
er and smaller to keep pace. At the middle marker, the glideslope
is about 200 feet above the ground - right at minimums, so if you
don’t see the runway at this point, initiate the missed-approach
procedure. A common error, with the runway in sight, is to “duck
under” the final segment of the glideslope. Don’t do it! Just “hold
what you’ve got,” and you’ll touch down about 1000 feet in from
the threshold with plenty of runway left on which to decelerate
and stop.