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78 CHAPTER 7. NAVIGATION, AUTOPILOTS, AND FLYING ON INSTRUMENTS
taking away power results in climbs and descents, respectively. The difference is that if you have
auto-throttle on the airplane, FLCH will automatically add or take away power for you to start
the climb or descent, whereas SPD will not.
The PTCH button controls the pitch sync function. Use this to hold the plane’s nose at a
constant pitch attitude. This is commonly used to just hold the nose somewhere until the pilot
decides what to do next.
The G/S button controls the glideslope flight function. This will fly the glideslope portion of
an ILS.
The VNAV button controls the vertical navigation function. This will automatically load altitudes
from the FMS (Flight Management System) into the autopilot for you in order to follow
route altitudes (as discussed in the section “Flying an FMS Plan” below).
The BC button controls the back course function. Every ILS on the planet has a little-known
second localizer that goes in the opposite direction as the inbound localizer. This is used for the
missed approach, allowing you to continue flying along the extended centerline of the runway, even
after passing over and beyond the runway. To save money, some airports will not bother to install
a new ILS at the airport to land on the same runway going the other direction, but instead let
you fly this second localizer backwards to come into the runway from the opposite direction of the
regular ILS! This is called a back course ILS.
Using the same ILS in both directions has its advantages (e.g., it’s cheaper), but there’s a
drawback: the needle deflection on your instruments is backwards when going the wrong way on
the ILS. Hit the BC autopilot button if you are doing this. It causes the autopilot to realize that
the needle deflection is backwards and still fly the approach.
Note that HSIs do not reverse the visible needle deflection in the back-course; you must turn the
housing that the deflection needle is mounted on around 180 degrees to fly the opposite direction.
Note also that the glideslope is not available on the back course, so you have to use the localizer
part of the procedure only.
7.3.1 Turning It On and Off
Before using the autopilot, it needs to be turned on. The autopilot power switch is labeled “Flight
Director Mode,” or simply “FLIGHT DIR.” It has OFF, ON, and AUTO modes.
If the flight director is OFF, nothing will happen when you try to use the autopilot. If it is ON,
then the autopilot will not physically move the airplane controls, but will rather move little target
wings on your artificial horizon that you can try to mimic as you fly. If you do this, you will be
following the guidance that the autopilot is giving you, even though you are the one actually flying.
The flight director, then, is following whatever autopilot mode you selected, and you, in turn, are
following the flight director to actually fly the plane. If the flight director is set to AUTO, then the
autopilot servos will actually fly the airplane according to the autopilot mode you have selected.
In other words, turning the flight director ON turns on the brains of the autopilot, displaying
the commands from the modes above on the horizon as little magenta wings you can follow. Turning
the Flight Director switch to AUTO turns on the servos of the autopilot, so the plane follows the
little magenta wings for you without you touching the stick.
Therefore, if you have a flight director switch, make sure it is in the right mode for the type of
autopilot guidance you want—none, flight director only, or servo-driven controls.
When you first turn the flight director to ON or AUTO, it will automatically engage in the
pitch sync and wing leveler modes, which will simply hold the craft’s current pitch and roll until
some other mode is selected. If the system is turned on with less than 7 degrees of bank, however,
the flight director will assume you want the wings level, and it will automatically do so for you.