The Coffee Bean & Tea Leaf(CBTL), Business strategy case study
5.15 Typical electronic digital aircraft systems
1. Module 5: Digital Techniques and
Electronic Instrument Systems
5.15 Typical Electronic-Digital Aircraft Systems
2. Overview
CMS & BITE: Computer Maintenance System & Built-In Test
Equipment
ACARS: Aircraft Communication Addressing and Reporting System
EFIS: Electronic Flight Instrument System
EICAS & ECAM
FBW: Fly-By-Wire
FMS: Fly Management System
GPS: Global Positioning System
INS / IRS: Inertial Navigation System / Inertial Reference System
TCAS: Traffic Collision Avoidance System
DFDR / CVR: Digital Flight Data Recorder / Cockpit Voice Recorder
5. BITE
Built-in Test Equipment:
A system is composed of LRUs, which can be computers,
sensors, probes, actuators etc. which perform specific
functions.
A part of each system is dedicated to functions such as:
monitoring, testing and troubleshooting.
This part of the system is the Built-in Test Equipment.
BITE can (a) perform error detection test (b) isolation:
identify the possible failed LRUs and give a snapshot of
the system when the failure occurred, (c) memorization:
record the error in a memory device.
The information are sent to the Centralized Maintenance
Computer.
7. Testing with BITE
Several kinds of tests:
Power-up test:
Ensuring compliance with safety objectives.
It is performed only on ground, because they disturb normal
operation.
They are performed after long power cuts (more than 200msec).
If the aircraft is airborne the test is limited to a few items to
enable a quick return to operation of the system:
CPU test
memory test
ARINC test
I/O test
configuration test
However, when we normally refer to power-up tests, we assume
the aircraft is on ground.
8. Testing with BITE
Cyclic tests (also called operation test):
They are carried out permanently, because they do not disturb normal
operation.
Examples: Watchdog test (i.e. CPU reset). RAM test.
System tests:
Tests available to the maintenance staff, for troubleshooting purposes.
Similar to ground power-up tests, but more complete.
Examples: Tests performed after the replacement of an LRU.
Specific tests:
Available only to specific systems.
They are performed to generate stimuli to other devices, such as actuators
or valves.
They have major effect on aircraft (such as automatic moving of flaps etc.)
They are performed only on ground by maintenance staff.
9. BITE Inside a Computer
Make a power up test when the computer starts-up
Operate normally and perform the cyclic tests.
If we are on ground, provide the option to do
system or specific tests. Otherwise, continue with
normal operation.
11. Aircraft Condition Monitoring System
Monitoring of engine, APU,
performance monitoring and
troubleshooting.
Collects, records and processes
aircraft system data.
ACMS data can be forwarded to
the MCDU, to a printer,
transmitted through ACARS etc.
12. ACMS architecture
It consists of two parts:
Data Management Unit (DMU): Handles and stores
system data.
Flight Data Interface Unit (FDIU):
Provides DMU with data from the engines, systems etc.
DMU
(Data
Management
Unit)
13. Electronic Library System
Collection and presentation of technical and
operational material relating to aircraft, in a digital
form.
Can be accessed by flight crews and maintenance
staff through computers.
It’s a database of guides and manuals, stored in a
computer and accessed by an LCD touch screen.
Usually, an ARINC 744A printer is connected to the
library system, for document printing.
ARINC 744A is the standard airborne printer protocol.
14. Aircraft Communication Addressing and
Reporting System
ACARS:
An air-ground
communication data
linked network.
It is used to transmit or
receive automatically
or manually
generated reports to
or from the ground
station.
ACARS protocol was
designed by ARINC.
Communication can be
transferred through
ground VHF stations or
SATCOM (Satellite
Communication).
15. Why ACARS?
Prior to ACARS development all communications
between aircraft and ground were VHF or HF voice
communications.
To reduce crew workload and ensure data integrity,
developed ACARS communication system.
16. VHF Usage
AM: KHz (Not used in aviation).
HF: 3 – 30MHz (Used in aviation for longer range, e.g.
when flying above Antarctic).
VHF: Above 30MHz (Normally used in aviation).
Note: Higher frequencies are
more easily absorbed by
objects.
17. Automatic ACARS messages
ACARS interface with FMS (Flight Management
Systems) enables the automatic receiving of weather
reports from the ground.
Major flight phases (OOOI):
Out of the gate, Off the ground, On the ground, and Into
the gate messages.
Engine reports in real time can be automatically sent
from the airplane to the airliners.
In case of failures during flight, real time information can
be uploaded by the manufacturers associated with the
fault.
18. Non-automatic messages: Interaction
between the crew and the ground.
Communication between the flight crew and the
ground is made through FMS (it’s similar to email).
Messages examples:
Weather
Winds
Clearances
…
After Air France Flight 477 it has been discussed to
make ACARS an online black-box, to retain flight
information in case of lost black-box.
19. How is an ACARS message propagates?
Through a VHF network:
Only applicable to land masses, where a VHF ground
network is installed.
Used for up to 200miles transmission range.
Through an HF network:
Used in areas such as the poles and oceans.
Completed in 2001.
Through satellites:
Provides world-wide coverage.
The message passes through an ACARS network
(through ARINC’s servers) to the operator’s center.
The operators center can be either CAA or a flight operator.
ACARS service providers are used to propagate the
message to the destination.
20. ACARS messages categories
2 types of messages:
Air Traffic Control: Messages from / to ATC. (e.g. clearance).
Aeronautical Operation Control: Messages from / to the base
(flight operation department). (e.g. fuel consumption, engine
performance etc.)
The message format is defined by a specific ARINC protocol.
Each message contains an address label.
Message Example:
ACARS mode: H Aircraft reg: D-AIRL [A321-131]
Message label: 1L [Off message] Block id: 9 Msg no: M23A
Flight id: LH3394 Org: LH06LT [Munich, Germany-Athen, Greece]
[Lufthansa]
Flight distance: appr. 1511km Flight time: appr. 1.7 hours
Message content: 00016234212AN((628D8UVPCR(GKTRRUBW
21. ACARS vs. CPDLC
Controller–pilot data link
communications
It is built on ACARS. The aim is to
reduce voice congestion.
It’s another communication system
between the flight crew and the flight
controller.
Similarities with ACARS:
Uses VHF, HF and Satellite.
Text messages.
Differences with ACARS:
Designed only for communication
between the flight crew and the
controller.
However, in Boeing 777 CPDLC
messages can be sent to the
company, as well.
22. The future of ACARS
ATN: Aeronautical
Telecommunications
Network
An integrated network
inspired from the
Internet architecture.
ACARS uses
character messages,
while ATN uses binary
format.
26. Airbus 320 Primary Flight Display
Flight Mode Annunciator
The flight mode annunciator (FMA),
shows:
Autopilot operation
AP/FD vertical and lateral modes
Approach capabilities
AP, FD, A/THR engagement
status.
Green color is “engaged”.
Blue color is “armed”.
is related to approach indications in column 4.
Magenta are target speed, altitude etc.
39. EIS Components
DMC: Digital
Management
Computer or
Symbol
Generator:
Generates data
in a compatible
format with the
display units.
Contain CPUs,
RAM, display
drivers, raster
generators etc.
In case of failure of
DMC1 or DMC2.
System Data Acquisition
concentrator
47. Fly-By-Wire
Fly-By-Wire (FBW) is a system that replaces the
conventional manual flight controls of an aircraft with
an electronic interface.
Flight control computers determine how to move the
actuators at each control surface to provide the
ordered response.
The movements of flight controls are converted to
electronic signals transmitted by wires.
Fly-By-Wire allows automatic signals sent by the
aircraft's computers to perform functions without the
pilot's input, as in systems that automatically help
stabilize the aircraft
48. Conventional Flight Control Systems vs. Fly-
By-Wire
Mechanical systems are heavy, non-accurate, prone
to failures and errors. They have limited ability to
compensate for changing aerodynamic conditions.
Fly-By-Wire implies a purely electrically signaled
control system.
Computer configured controls: A computer system is
interposed between the operator and the final actuator.
Fly-By-Wire examples:
Side-sticks
Control yokes
…
49. Fly-By-Wire Philosophy
The mechanical system that
controls the servomechanism,
which moves the surface is
replaced by a computer.
50. Advantages of Fly-By-Wire
Due to the complex calculations that computers can
make, they can make decisions without the pilot
input. e.g. Automatic stability systems.
Safety:
More than one wires can be easily used to ensure the
propagation of a signal.
More than one computers can be easily used, to ensure
proper operation when one computer fails.
BITE
Weight Saving
51. History of Fly-By-Wire
Tupolev ANT-20 in 1930:
The first airplane, where
long runs of mechanical
systems were replaced by
electrical systems.
Concorde (1986):
Mechanical servo valves
were replaced with
electrically controlled servo
valves, operated by an
analogue electronic
controller.
More sophisticated
analogue computers were
used in early versions of
F-16.
52. Digital Fly-By-Wire
In digital fly-by-wire flight
control systems, the signal
processing is done by digital
computers and the pilot literally
can "fly-via-computer".
The programming of the digital
computers enables flight
envelope protection.
Aircraft protection, reduced pilot’s
workload.
FADEC: Full Authority Digital
Engine Control
Permits control of flight surfaces
and engine autothrottles to be
fully integrated.
53. FADEC advantages
FADEC contains a digital computer and a unit that controls
the engine.
Allows maximum performance to be obtained from the
engine.
Protection from dangerous situations such as low-speed
stall or overstressing by flight envelope protection.
the flight control systems commands the engines to increase
thrust without pilot intervention.
In economy cruise modes, the flight control systems adjust
the throttles and fuel tank selections more precisely than all
but the pilots.
54. Further Fly-By-Wire developments
Fly-by-optics
Signal is transferred by light instead of current.
Power-by-wire
Having eliminated the mechanical transmission circuits in
fly-by-wire flight control systems, the next step is to
eliminate the bulky and heavy hydraulic circuits.
Fly-by-wireless
Intelligent Flight Control System
In case of a failure leading to a crash, computers make
complex calculations to adjust the flight controls in a
proper position to save the aircraft.
It is believed that enchantments are mostly software upgrades
to the existing infrastructures.
56. Flight Management System: Introduction
FMS basic operation:
Compares the pilot selected
flight plan with the actual
horizontal and vertical aircraft
position.
In case of difference between
them, the FMS makes a
steering and thrust command.
The FMS input and output
device is the:
CDU: Control Display Unit or
MCDU: Multifunction Control
Display Unit
57. FMS operations
The pilot sets the flight plan through the MCDU.
A database with airports, runways, waypoints is used.
FMS automatically selects optimal parameters
e.g. climb ration, optimal speed etc.
Shows information about the flight plan on MCDU.
Exchanges information and commands the Autopilot
/ Autothrottle Flight System AFS.
Accepts DME and VOR inputs.
Gives information to the EFIS displays.
58. FMS Description
Navigation:
FMS uses information form its database to automatically tune the
navaids (ILS, VOR, DME).
Database must be updated every 28 days.
Performance:
The FMS calculates the shortest possible flying time at the lowest
fuel consumption. Can give predictions of fuel quantities and
arrival times at future points in the flight plan.
Guidance:
The FMS compares the desired position of the aircraft according
to the flight plan, with the actual aircraft position. If there is a
difference, FMS commands the AFS to bring the aircraft to the
desired position.
Position and velocity are calculated using the IRS, GPS, VOR and
DME.
EFIS Display:
FMS is the primary source of information displayed on EFIS.
59. Setting up the FMS
INIT:
Set the take off runway and destination.
Set fuels.
Insert the waypoints.
F-PLN:
Check or modify the flight plan.
Eliminate discontinuities.
Performance:
Set flaps, weather and other information that
affects performance for each flight phase.
Flight plan is displayed on ND.
60. FMS block diagram
Flight Management Computer :
Performs the Navigation and performance calculations.
Stores the database and the selected flight plan.
Tunes to navaids.
Commands the AFS.
Makes EFIS display calculations
63. GNSS
GNSS (Global Navigation Satellite System) is an
umbrella term for systems which are used to
navigate and determine current position based on
signals received from dedicated navigation satellites.
4 most important GNSS systems:
GPS
GEONASS
Galileo
Compass
64. Principles of Operation
All satellite navigation systems
use the same principle as DME
(Distance Measuring Equipment):
The receivers measure the time it
takes for a radio signal (around
1.5GHz) to travel from a
transmitter in a satellite at a known
point in space.
The receiver’s computer calculates
the distance for more than one
satellites.
65. Satellites and Space Segment
There are 6 orbital planes with 4
satellites in each plane.
Each plane is inclined 55 degrees
relative to the equator.
In the American GPS (NAVSTAR),
there are 24 satellites at 11,000nm
moving around the globe and
return to the same position after 12
hours.
66. Errors in Transmission
After the third
measurement, one of the
two possible points can
be discarded, since it is
far from the earth
surface.
Possible errors that
degrade the accuracy:
Atmospheric conditions
Noise due to sunspot
activity.
Satellite clock drift:
Variations of the clock of
the satellite transmitter
clock. (1nsec drift causes
1ft. distance error).
Calculations from a 4th
satellite are needed to
eliminate the effects of
these errors.
67. The European GPS System
A system of 30 satellites (under
development).
Higher accuracy that the NAVSTAR (down
to less than a meter). .
68. Supplementary Systems needed for aircraft
Navigation
Aircraft-based Augmentation
Systems:
Sensors on the aircraft to detect the
quality of the GNSS data received
and correct them if necessary.
Satellite-based Augmentation
Systems:
Geostationary satellites detect errors
and correct GNSS signals
transmitted to users.
They are limited to certain regions of
the world.
WAAS (USA), EGNOS (Europe).
Ground-based Augmentation
Systems:
Ground stations around the airports
enhance positioning accuracy.
They are considered a long term
replacement to ILS.
Example: Differential GPS: A
ground-station propagates the GPS
error to GPS receivers.
70. Accelerometer
Acceleration moves the
strings to the opposite
direction of the
movement.
The acceleration of
indication can be
integrated once to give
velocity and once more
to provide distance.
On the aircraft, induction
is are used.
By knowing the starting
position (IRS alignment)
an aircraft can calculate
the distance covered.
71. The Gyroscope principle
When the rotor spins, no
matter how the plane
rotates on the yaw, the
plane at which gyro
rotates remains the
same.
The gimbal will move so,
the spin axis remain the
same, no matter how it
will rotate.
72. Inertial Navigation System
Mechanical gyros:
A gyro along with
an electrical
system to
measure the
distance between
the gyro spin axis
and the gimbal
movement.
73. Inertial Reference System
Mechanical gyros are
replaced with laser gyros,
for greater accuracy.
Movement of gimbal is
measured with the
difference between arrival
times of two laser beams.
When rotation takes place,
the orientation of the
mirrors changes, thus the
beams reach at different
times the detector.
75. TCAS: Traffic Alert Collision Avoidance
System
System designed to
reduce the incidence
of mid-air collisions
between aircrafts.
When another
aircraft appears in
the vicinity an
automatic
negotiation is being
made between the 2
aircrafts to avoid
collision.
Information are
displayed in EHSI
(Electronic
Horizontal Situation
Indicator)
A number next to each
aircraft shows the height
of each aircraft in
comparison to this one.
76. TCAS Alerts
Traffic Advisory (TA):
Pilots are instructed to
initiate a visual search for
the traffic causing the TA.
If the traffic is visually
acquired, pilots are
instructed to maintain visual
separation from the traffic.
Resolution Advisory (RA):
Pilots are expected to
respond immediately to the
RA.
This means that aircraft will
at times have to maneuver
contrary to ATC instructions
or disregard ATC
instructions.
Clear of Conflict (CC):
Pilots shall promptly return
to the terms of the ATC
instruction.
78. TCAS Advisories
Type Text Meaning Required action[1][2][5]
TA Traffic; traffic.
Intruder near both horizontally and
vertically.
Attempt visual contact, and be
prepared to maneuver if an RA
occurs.
RA Climb; climb. Intruder will pass below Begin climbing at 1500–2000 ft/min
RA Descend. Descend. Intruder will pass above. Begin descending at 1500–2000 ft/min
RA Increase climb. Intruder will pass just below Climb at 2500 – 3000 ft/min.
RA Increase descent. Intruder will pass just above. Descend at 2500 – 3000 ft/min.
RA Reduce climb. Intruder is probably well below. Climb at a slower rate.
RA Reduce descent. Intruder is probably well above. Descend at a slower rate.
RA Climb; climb now.
Intruder that was passing above,
will now pass below.
Change from a descent to a climb.
RA Descend; descend now.
Intruder that was passing below,
will now pass above.
Change from a climb to a descent.
RA
Maintain vertical speed;
maintain.
Intruder will be avoided if vertical
rate is maintained.
Maintain current vertical rate.
RA Adjust vertical speed; adjust.
Intruder considerably away, or
weakening of initial RA.
Begin to level off.
RA Monitor vertical speed.
Intruder ahead in level flight, above
or below.
Remain in level flight.
RA Crossing.
Passing through the intruder's
level. Usually added to any other
RA.
Proceed according to the associated
RA.
CC Clear of conflict. Intruder is no longer a threat.
Return promptly to previous ATC
clearance.
80. Flight Data Recorder (FDR)
Flight Data Recorders store snapshots
of the following information:
Altitude
Heading
Airspeed
Acceleration
Thrust on each engine
Use of Autopilot
Angle of attack
Air temperature
…
These information are from the same
sources that supply the flight crew.
Recording begins with the start of the
first engine and ceases at shut-down of
the last engine.
Must survive impact velocity of
270knots.
Each snapshot is taken 1-2 times per
second.
Can record from 17 – 25 hours
continuously.
Crash
survivable
memory unit.
Underwater
Locator
Beacon
(emitting for
30 days up to
20,000 ft.)
Power Supply
81. Cockpit Voice Recorder (CVR)
Often referred as “black box”.
Records all the communication
transmitted or received by to /
from the flight deck.
Voice communication between
the flight crew.
All sounds in the cockpit, e.g.
audio signals, sound alarms.
Must be capable of recording
for at least 2 hours.
Recording begins with the start
of the first engine and ceases
at shut-down of the last engine.
