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not installed, or in emergency operation, the heading must
be checked against the magnetic compass occasionally and
reset with the course select knob.
Attitude Direction Indicator (ADI)
Advances in attitude instrumentation combine the gyro
horizon with other instruments such as the HSI, thereby
reducing the number of separate instruments to which the
pilot must devote attention. The attitude direction indicator
(ADI) is an example of such technological advancement.
A flight director incorporates the ADI within its system,
which is further explained below (Flight Director System).
However, an ADI need not have command cues; however,
it is normally equipped with this feature.
Flight Director System (FDS)
A Flight Director System (FDS) combines many instruments
into one display that provides an easily interpreted
understanding of the aircraft’s flight path. The computed
solution furnishes the steering commands necessary to obtain
and hold a desired path.
Major components of an FDS include an ADI, also called
a Flight Director Indicator (FDI), an HSI, a mode selector,
and a flight director computer. It should be noted that a
flight director in use does not infer the aircraft is being
manipulated by the autopilot (coupled), but is providing
steering commands that the pilot (or the autopilot, if coupled)
follows.
Typical flight directors use one of two display systems for
steerage. The first is a set of command bars, one horizontal
and one vertical. The command bars in this configuration
are maintained in a centered position (much like a centered
glide slope). The second uses a miniature aircraft aligned to
a command cue.
A flight director displays steerage commands to the pilot on
the ADI. As previously mentioned, the flight director receives
its signals from one of various sources and provides that to the
ADI for steerage commands. The mode controller provides
signals through the ADI to drive the steering bars, e.g., the
3-24
Figure 3-39. A Typical Cue That a Pilot Would Follow.
Figure 3-40. Components of a Typical Flight Director System.
pilot flies the aircraft to place the delta symbol in the V of the
steering bars. “Command” indicators tell the pilot in which
direction and how much to change aircraft attitude to achieve
the desired result.
The computed command indications relieve the pilot of
many of the mental calculations required for instrument
flight. The yellow cue in the ADI [Figure 3-39] provides all
steering commands to the pilot. It is driven by a computer that
receives information from the navigation systems, the ADC,
AHRS, and other sources of data. The computer processes this
information, providing the pilot with a single cue to follow.
Following the cue provides the pilot with the necessary threedimensional
flight trajectory to maintain the desired path.
One of the first widely used flight directors was developed
by Sperry and was called the Sperry Three Axis Attitude
Reference System (STARS). Developed in the 1960s, it was
commonly found on both commercial and business aircraft
alike. STARS (with a modification) and successive flight
directors were integrated with the autopilots and aircraft
providing a fully integrated flight system.
The flight director/autopilot system described below is
typical of installations in many general aviation aircraft.
The components of a typical flight director include the mode
controller, ADI, HSI, and annunciator panel. These units are
illustrated in Figure 3-40.
The pilot may choose from among many modes including
the HDG (heading) mode, the VOR/LOC (localizer tracking)
mode, or the AUTO Approach (APP) or G/S (automatic
capture and tracking of instrument landing system (ILS)
localizers and glide path) mode. The auto mode has a fully
automatic pitch selection computer that takes into account
aircraft performance and wind conditions, and operates once
the pilot has reached the ILS glide slope. More sophisticated
systems allow more flight director modes.
Integrated Flight Control System
The integrated flight control system integrates and merges
various systems into a system operated and controlled by one
principal component. Figure 3-41 illustrates key components
of the flight control system that was developed from the
onset as a fully integrated system comprised of the airframe,
autopilot, and flight director system. This trend of complete
integration, once seen only in large commercial aircraft, are
now becoming common in the general aviation field.
Autopilot Systems
An autopilot is a mechanical means to control an aircraft
　
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