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have a separate hour meter to record time in service
for maintenance purposes. Automatic overtemperature
protection is provided by a thermal switch mounted on
the unit, which cannot be accessed in flight. This
requires the pilot or mechanic to actually visually
inspect the unit for possible heat damage in order to
reset the switch.
When finished with the combustion heater, a cool
down period is required. Most heaters require that outside
air be permitted to circulate through the unit for at
least 15 seconds in flight, or that the ventilation fan be
operated for at least 2 minutes on the ground. Failure
to provide an adequate cool down will usually trip the
thermal switch and render the heater inoperative until
the switch is reset.
FLIGHT DIRECTOR/AUTOPILOT
Flight director/autopilot (FD/AP) systems are common
on the better-equipped multiengine airplanes. The
system integrates pitch, roll, heading, altitude, and
radio navigation signals in a computer. The outputs,
called computed commands, are displayed on a flight
command indicator, or FCI. The FCI replaces the
conventional attitude indicator on the instrument
panel. The FCI is occasionally referred to as a flight
director indicator (FDI), or as an attitude director
indicator (ADI). The entire flight director/autopilot
system is sometimes called an integrated flight control
system (IFCS) by some manufacturers. Others
may use the term “automatic flight control system
(AFCS).”
The FD/AP system may be employed at three different
levels.
• Off (raw data).
• Flight director (computed commands).
• Autopilot.
With the system off, the FCI operates as an ordinary
attitude indicator. On most FCIs, the command bars
are biased out of view when the flight director is off.
The pilot maneuvers the airplane as though the system
were not installed.
To maneuver the airplane using the flight director, the
pilot enters the desired modes of operation (heading,
altitude, nav intercept, and tracking) on the FD/AP
mode controller. The computed flight commands are
then displayed to the pilot through either a single-cue
or dual-cue system in the FCI. On a single-cue system,
the commands are indicated by “V” bars. On a
dual-cue system, the commands are displayed on
two separate command bars, one for pitch and one
for roll. To maneuver the airplane using computed
commands, the pilot “flies” the symbolic airplane
of the FCI to match the steering cues presented.
On most systems, to engage the autopilot the flight
director must first be operating. At any time thereafter,
the pilot may engage the autopilot through the mode
controller. The autopilot then maneuvers the airplane
to satisfy the computed commands of the flight
director.
Like any computer, the FD/AP system will only do
what it is told. The pilot must ensure that it has been
properly programmed for the particular phase of flight
desired. The armed and/or engaged modes are usually
displayed on the mode controller or separate annunciator
lights. When the airplane is being hand-flown, if
the flight director is not being used at any particular
moment, it should be off so that the command bars are
pulled from view.
Prior to system engagement, all FD/AP computer and
trim checks should be accomplished. Many newer
systems cannot be engaged without the completion of
a self-test. The pilot must also be very familiar with
various methods of disengagement, both normal and
emergency. System details, including approvals and
limitations, can be found in the supplements section
of the AFM/POH. Additionally, many avionics manufacturers
can provide informative pilot operating
guides upon request.
YAW DAMPER
The yaw damper is a servo that moves the rudder in
response to inputs from a gyroscope or accelerometer
that detects yaw rate. The yaw damper minimizes
motion about the vertical axis caused by turbulence.
(Yaw dampers on sweptwing airplanes provide
another, more vital function of damping dutch roll
characteristics.) Occupants will feel a smoother ride,
particularly if seated in the rear of the airplane, when
the yaw damper is engaged. The yaw damper should
be off for takeoff and landing. There may be additional
restrictions against its use during single-engine operation.
Most yaw dampers can be engaged independently
of the autopilot.
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ALTERNATOR/GENERATOR
Alternator or generator paralleling circuitry matches
the output of each engine’s alternator/generator so that
　
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