Figure 5-41. The S-TEC/Meggit Corporation Integrated Autopilot installed in the Cirrus.
Figure 5-42. An Autopilot by Century.
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 5-41 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 FDS. This trend of complete integration, once
seen only in large commercial aircraft, is now becoming
common in general aviation.
Autopilot Systems
An autopilot is a mechanical means to control an aircraft
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.
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 rate-
based information to benefit from the attributes of both systems
while newer autopilots are digital. Figure 5-42 illustrates an
autopilot by Century.
Figure 5-43 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.
Figure 3-43. S-Tec auto pilot
NO PITCH INFORMATION
L R
TURN COORDINATOR
2 MIN.
PWR
ST HD TRK
LO HI
RDY
ALT TRIM
UP
DN
20 20
I0 I0
2 0
I 0
Figure 5-43. A diagram layout of an autopilot by S-Tec.
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 (RNAV) capability.
Long-range 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.
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 pre-
loaded 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
a flight plan consisting of dozens of waypoints, avoiding
the tedious typing of data and the error potential of latitude/
longitude coordinates. Rather than simply navigating point-
Figure 5-44. A Control Display Unit (CDU) used to control the
flight management system (FMS).
to-point, the master system would be able to maneuver the
aircraft, permitting use of the system for terminal procedures
including departures, arrivals, and approaches. The system
would be able to automate any aspect of manual pilot
navigation of the aircraft. When the first system, called the
UNS-1, was released by Universal in 1982, it was called a
flight management system (FMS). [Figure 5-44]
An FMS uses an electronic database of worldwide
navigational data including navigation aids, airways and
intersections, Standard Instrument Departures (SIDs),
STARs, and Instrument Approach Procedures (IAPs) together
with pilot input through a CDU to create a flight plan. The
FMS provides outputs to several aircraft systems including
desired track, bearing and distance to the active waypoint,
lateral course deviation and related data to the flight guidance
system for the HSI displays, and roll steering command for
the autopilot/flight director system. This allows outputs from
the FMS to command the airplane where to go and when and
how to turn. To support adaptation to numerous aircraft types,
an FMS is usually capable of receiving and outputting both
analog and digital data and discrete information. Currently,
electronic navigation databases are updated every 28 days.
The introduction of the Global Positioning System (GPS) has
provided extremely precise position at low cost, making GPS
the dominant FMS navigation sensor today. Currently, typical
FMS installations require that air data and heading information
be available electronically from the aircraft. This limits FMS
usage in smaller aircraft, but emerging technologies allow
this data from increasingly smaller and less costly systems.
Some systems interface with a dedicated Distance Measuring
Equipment (DME) receiver channel under the control of the
FMS to provide an additional sensor. In these systems, the
FMS determines which DME sites should be interrogated
for distance information using aircraft position and the
navigation database to locate appropriate DME sites. The
FMS then compensates aircraft altitude and station altitude
with the aid of the database to determine the precise distance
to the station. With the distances from a number of sites the
FMS can compute a position nearly as accurately as GPS.
Aimer visualized three-dimensional aircraft control with an
FMS. Modern systems provide Vertical Navigation (VNAV) as
well as Lateral Navigation (LNAV) allowing the pilot to create
a vertical flight profile synchronous with the lateral flight plan.
Unlike early systems, such as Inertial Reference Systems (IRS)
that were only suitable for en route navigation, the modern
FMS can guide an aircraft during instrument approaches.
Today, an FMS provides not only real-time navigation
capability but typically interfaces with other aircraft systems
providing fuel management, control of cabin briefing and
display systems, display of uplinked text and graphic weather
data and air/ground data link communications.
Electronic Flight Instrument Systems
Modern technology has introduced into aviation a new
method of displaying flight instruments, such as electronic
flight instrument systems, integrated flight deck displays, and
others. For the purpose of the practical test standards, any
flight instrument display that utilizes LCD or picture tube like
displays is referred to as “electronic flight instrument display”
and/or a glass flight deck. In general aviation there is typically
a primary flight display (PFD) and a multi-function display
(MFD). Although both displays are in many cases identical,
the PFD provides the pilot instrumentation necessary for
flight to include altitude, airspeed, vertical velocity, attitude,
heading and trim and trend information.
Glass flight decks (a term coined to describe electronic flight
instrument systems) are becoming more widespread as cost
falls and dependability continually increases. These systems
provide many advantages such as being lighter, more reliable,
no moving parts to wear out, consuming less power, and
replacing numerous mechanical indicators with a single glass
display. Because the versatility offered by glass displays is
much greater than that offered by analog displays, the use of
such systems only increases with time until analog systems
are eclipsed.
Primary Flight Display (PFD)
PFDs provide increased situational awareness (SA) to the
pilot by replacing the traditional six instruments used for
instrument flight with an easy-to-scan display that provides
the horizon, airspeed, altitude, vertical speed, trend, trim,
Figure 5-46. The benefits of realistic visualization imagery, as
illustrated by Synthetic Vision manufactured by Chelton Flight
Systems. The system provides the pilot a realistic, real-time, three-
dimensional depiction of the aircraft and its relation to terrain
around it.
XPDR 5537 IDNT LCL10:12:34
INSET PFD CDI XPDR IDENT TMR/REF NRST ALERTS
VOR 1
270°
T AS 106KT
OA T 6°C
NA V1 108.00 113.00
NA V2 108.00 110.60
134.000 118.000 COM1
123.800 118.000 COM2
WPT _ _ _ _ _ _ DIS _ _ . _ NM DTK _ _ _° TRK 360°
OA T 6°C
Figure 5-45. Two primary flight displays (Avidyne on the left and Garmin on the right).
rate of turn among other key relevant indications. Examples
of PFDs are illustrated in Figure 5-45.
Synthetic Vision
Synthetic vision provides a realistic depiction of the aircraft
in relation to terrain and flightpath. Systems such as those
produced by Chelton Flight Systems, Universal Flight
Systems, and others provide for depictions of terrain and
course. Figure 5-46 is an example of the Chelton Flight
System providing both 5-dimensional situational awareness
and a synthetic highway in the sky, representing the desired
flightpath. Synthetic vision is used as a PFD, but provides
guidance in a more normal, outside reference format.
Multi-Function Display (MFD)
In addition to a PFD directly in front of the pilot, an MFD
that provides the display of information in addition to primary
flight information is used within the flight deck. [Figure 5-47]
Information such as a moving map, approach charts, Terrain
Awareness Warning System, and weather depiction can all
be illustrated on the MFD. For additional redundancy both
the PFD and MFD can display all critical information that
the other normally presents thereby providing redundancy
(using a reversionary mode) not normally found in general
aviation flight decks.
Advanced Technology Systems
Automatic Dependent Surveillance—Broadcast
(ADS-B)
Although standards for Automatic Dependent Surveillance
(Broadcast) (ADS-B) are still under continuing development,
the concept is simple: aircraft broadcast a message on
a regular basis, which includes their position (such as
latitude, longitude and altitude), velocity, and possibly
other information. Other aircraft or systems can receive this
information for use in a wide variety of applications. The
key to ADS-B is GPS, which provides three-dimensional
position of the aircraft.
As an simplified example, consider air-traffic radar. The radar
measures the range and bearing of an aircraft. The bearing is
measured by the position of the rotating radar antenna when it
receives a reply to its interrogation from the aircraft, and the
range by the time it takes for the radar to receive the reply.
An ADS-B based system, on the other hand, would listen
for position reports broadcast by the aircraft. [Figure 5-48]
These position reports are based on satellite navigation
systems. These transmissions include the transmitting
aircraft’s position, which the receiving aircraft processes into
Figure 5-47. Example of a multi-function display (MFD).
usable pilot information. The accuracy of the system is now
determined by the accuracy of the navigation system, not
measurement errors. Furthermore the accuracy is unaffected
by the range to the aircraft as in the case of radar. With radar,
detecting aircraft speed changes require tracking the data and
changes can only be detected over a period of several position
updates. With ADS-B, speed changes are broadcast almost
instantaneously and received by properly equipped aircraft.
Additionally, other information can be obtained by properly
equipped aircraft to include notices to airmen (NOTAM),
weather, etc. [Figures 5-49 and 5-50] At the present time,
ADS-B is predominantly available along the east coast of
the United States where it is matured.
Safety Systems
Radio Altimeters
A radio altimeter, commonly referred to as a radar altimeter,
is a system used for accurately measuring and displaying the
height above the terrain directly beneath the aircraft. It sends
a signal to the ground and processes the timed information.
Its primary application is to provide accurate absolute altitude
information to the pilot during approach and landing. In
advanced aircraft today, the radar altimeter also provides its
information to other onboard systems such as the autopilot
and flight directors while they are in the glideslope capture
mode below 200-300 feet above ground level (AGL).
A typical system consists of a receiver-transmitter (RT)
unit, antenna(s) for receiving and transmitting the signal,
and an indicator. [Figure 5-51] Category II and III precision
approach procedures require the use of a radar altimeter and
specify the exact minimum height above the terrain as a
decision height (DH) or radio altitude (RA).
Traffic Advisory Systems
Traffic Information System
The Traffic Information Service (TIS) is a ground-based
service providing information to the flight deck via data
link using the S-mode transponder and altitude encoder. TIS
improves the safety and efficiency of “see and avoid” flight
through an automatic display that informs the pilot of nearby
traffic. The display can show location, direction, altitude
and the climb/descent trend of other transponder-equipped
aircraft. TIS provides estimated position, altitude, altitude
Figure 5-48. Aircraft equipped with Automatic Dependent Surveillance—Broadcast (ADS-B) continuously broadcast their identification,
altitude, direction, and vertical trend. The transmitted signal carries significant information for other aircraft and ground stations alike.
Other ADS-equipped aircraft receive this information and process it in a variety of ways. It is possible that in a saturated environment
(assuming all aircraft are ADS equipped), the systems can project tracks for their respective aircraft and retransmit to other aircraft
their projected tracks, thereby enhancing collision avoidance. At one time, there was an Automatic Dependent Surveillance—Addressed
(ADS-A) and that is explained in the Pilot’s Handbook of Aeronautical Knowledge.
trend, and ground track information for up to several aircraft
simultaneously within about 7 NM horizontally, 3,500 feet
above and 3,500 feet below the aircraft. [Figure 5-52] This
data can be displayed on a variety of MFDs. [Figure 5-53]
Figure 5-54 displays the pictorial concept of the traffic
information system. Noteworthy is the requirement to have
Mode S and that the ground air traffic station processes the
Mode S signal.
Traffic Alert Systems
Traffic alert systems receive transponder information from
nearby aircraft to help determine their relative position to the
equipped aircraft. They provide three-dimensional location
of other aircraft [Figures 5-55, 5-56, and 5-57] and are cost
effective alternatives to TCAS equipage for smaller aircraft.
Traffic Avoidance Systems
Traffic Alert and Collision Avoidance System (TCAS)
The TCAS is an airborne system developed by the FAA that
operates independently from the ground-based ATC system.
TCAS was designed to increase flight deck awareness of
proximate aircraft and to serve as a “last line of defense” for
the prevention of mid-air collisions.
There are two levels of TCAS systems. TCAS I was developed
to accommodate the general aviation (GA) community and
the regional airlines. This system issues traffic advisories
(TAs) to assist pilots in visual acquisition of intruder aircraft.
TCAS I provides approximate bearing and relative altitude
of aircraft with a selectable range. It provides the pilot with
TA alerting him or her to potentially conflicting traffic. The
pilot then visually acquires the traffic and takes appropriate
action for collision avoidance.
Figure 5-49. An aircraft equipped with ADS will receive identification, altitude in hundreds of feet (above or below using + or–), direction
of the traffic, and aircraft descent or climb using an up or down arrow. The yellow target is an illustration of how a non-ADS equipped
aircraft would appear on an ADS-equipped aircraft’s display.
Figure 5-50. An aircraft equipped with ADS has the ability to upload and display weather.
GS 250 4.0NM
UPS350 LRG
GS 240
120° /15
SDF
42 NM
11:10
VEC 1.0 MIN
-27 ALT +27
+10
FDX514
+12
-08
ABX123
UPS350
+09
Suveillance ADS.
+05
-09
UPS189
E 12 15 S
Aircraft direction
Aircraft identification
Altitude in relation
to your aircraft
Aircraft is descending
IN Out Pan WX Data Link
Service:
Available
Zoom:
20nm
10.0
Weather ADS-B.