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using electrical, hydraulic, or digital systems. Autopilots can
control three axes of the aircraft: roll, pitch, and yaw. Most
autopilots in general aviation control roll and pitch.
Autopilots also function using different methods. The first
is position based. That is, the attitude gyro senses the degree
of difference from a position such as wings level, a change
in pitch, or a heading change.
3-25
Figure 3-41. The S-TEC/Meggit Corporation Integrated Autopilot Installed in the Cirrus.
Figure 3-42. An Autopilot by Century.
Determining whether a design is position based and/or rate
based lies primarily within the type of sensors used. In order
for an autopilot to possess the capability of controlling an
aircraft’s attitude (i.e., roll and pitch), that system must be
provided with constant information on the actual attitude
of that aircraft. This is accomplished by the use of several
different types of gyroscopic sensors. Some sensors are
designed to indicate the aircraft’s attitude in the form of
position in relation to the horizon, while others indicate rate
(position change over time).
Rate-based systems use the turn-and-bank sensor for the
autopilot system. The autopilot uses rate information on
two of the aircraft’s three axes: movement about the vertical
axis (heading change or yaw) and about the longitudinal
axis (roll). This combined information from a single sensor
is made possible by the 30° offset in the gyro’s axis to the
longitudinal axis.
Other systems use a combination of both position and ratebased
information to benefit from the attributes of both systems
while newer autopilots are digital. Figure 3-42 illustrates an
autopilot by Century.
Figure 3-43 is a diagram layout of a rate-based autopilot by
S-Tec, which permits the purchaser to add modular capability
form basic wing leveling to increased capability.
Flight Management Systems (FMS)
In the mid-1970s, visionaries in the avionics industry such
as Hubert Naimer of Universal, and followed by others such
as Ed King, Jr., were looking to advance the technology of
aircraft navigation. As early as 1976, Naimer had a vision
of a “Master Navigation System” that would accept inputs
from a variety of different types of sensors on an aircraft
and automatically provide guidance throughout all phases
of flight.
At that time aircraft navigated over relatively short distances
with radio systems, principally VOR or ADF. For long-range
flight inertial navigation systems (INS), Omega, Doppler,
and Loran were in common use. Short-range radio systems
usually did not provide area navigation capability. Longrange
systems were only capable of en route point-to-point
navigation between manually entered waypoints described
as longitude and latitude coordinates, with typical systems
containing a limited number of waypoints.
3-26
Figure 3-43. A Diagram Layout of an Autopilot by S-Tec.
Figure 3-44. A Control Display Unit (CDU) Used to Control the
Flight Management System.
The laborious process of manually entering cryptic latitude
and longitude data for each flight waypoint created high
crew workloads and frequently resulted in incorrect data
entry. The requirement of a separate control panel for each
long-range system consumed precious flight deck space and
increased the complexity of interfacing the systems with
display instruments, flight directors, and autopilots.
The concept employed a master computer interfaced with all
of the navigation sensors on the aircraft. A common control
display unit (CDU) interfaced with the master computer would
provide the pilot with a single control point for all navigation
systems, thereby reducing the number of required flight deck
panels. Management of the various individual sensors would
be transferred from the pilot to the new computer.
Since navigation sensors rarely agree exactly about position,
Naimer believed that blending all available sensor position
data through a highly sophisticated, mathematical filtering
system would produce a more accurate aircraft position. He
called the process output the “Best Computed Position.” By
using all available sensors to keep track of position, the system
could readily provide area navigation capability. The master
computer, not the individual sensors, would be integrated into
the airplane, greatly reducing wiring complexity.
To solve the problems of manual waypoint entry, a preloaded
database of global navigation information would
be readily accessible by the pilot through the CDU. Using
such a system a pilot could quickly and accurately construct
　
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