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7.3. USING THE AUTOPILOT 79
With the flight director set to the right mode, you can engage the autopilot functions by simply
pressing the desired button in the instrument panel. To turn off an autopilot function, simply hit
its button once again. When all other autopilot functions are turned off, the autopilot will revert
to the default functions—pitch and roll hold modes.
To turn the autopilot off altogether, simply turn the FLIGHT DIR switch to OFF. Alternatively,
assign a key or joystick button to turn it off in the Joystick & Equipment dialog box of X-Plane.
7.3.2 Using the Controls
With the autopilot turned on (either to the flight director-only mode or the servo-driven control
mode), you are ready to use the autopilot functions. We will discuss when it would be appropriate
to use some of the most common functions.
7.3.2.1 Wing Leveler and Pitch Sync
Hit either the wing leveler (WLV) or the pitch sync (PTCH) to hold the current roll and pitch
attitude, respectively. This is useful when switching between autopilot functions.
7.3.2.2 Heading, Altitude, Vertical Speed, Speed Hold, Flight Level Change, and
Auto-Throttle
Hit the heading hold (HDG), altitude hold (ALT), vertical speed (V/S), speed hold (SPD), flight
level change (FLCH), or auto-throttle (ATHR) buttons and the autopilot will maintain whatever
values are entered into their respective selectors. For the sake of smooth transitions, many of these
values will be set by default to your current speed or altitude at the moment the autopilot function
buttons are hit.
If you want the autopilot to guide the aircraft to a new altitude, you have to ask yourself: Do
you want the airplane to hold a constant vertical speed to reach that new altitude, or a constant
airspeed to reach it? Since airplanes are most efficient at some constant indicated airspeed, climbing
by holding a constant airspeed is usually most efficient.
Regardless, we’ll start with the vertical speed case.
Imagine you are flying along at 5,000 feet and you hit ALT, causing the autopilot to store your
current altitude of 5,000 feet. Now, though, you want to climb to 9,000 feet. You would first dial
9,000 into the altitude window. The plane will not go there yet; before it will, you must choose how
you want to get to this new altitude.
If you decide to get there via a constant vertical speed, hit the V/S button and the plane
will capture your current vertical speed (possibly 0). Then, simply dial the VVI (vertical velocity
indicator) up or down to set how fast your will reach your target of 9,000 feet. When you get to
9,000 feet, the autopilot will automatically disengage the vertical speed mode and drop right back
into altitude mode at your new altitude.
Now, to get to your new altitude via a given airspeed (as airliners do), after dialing in 9,000
feet in the altitude window, you would hit the FLCH or SPD buttons. This will cause the plane to
pitch the nose up or down to maintain your current indicated airspeed. Now, simply add a dose of
power (if needed) to cause the nose of the plane to rise (which the autopilot will command in order
to keep the speed from increasing). When you reach 9,000 feet, the autopilot will leave speed-hold
mode and go into altitude-hold mode, holding 9,000 feet until further notice.
As you can see, both the airspeed and vertical speed modes will be maintained until you reach
the specified altitude, at which point the autopilot will abandon that mode and go into altitudehold
mode. The same thing will happen with the glideslope control. If the glideslope is armed (that