Avionics Systems

BASCEC 603

James A. Baskaradas
 Acknowledgement

All the materials presented

are from the internet
resources
UNIT 2 :Digital Avionics Architecture:

• Avionics system architecture

• Data buses - MIL-STD-1533B
• ARINC – 420 – ARINC – 629
• Electronic display
• EFIS (Electronic flight instrument system)
• Electronic Instruments for Engine & Airframe
system control
• EICAS (Engine indicating and crew alerting
system)
• ECAM (Electronic centralized aircraft monitoring
• Auto throttle system
 Avionics cost ?
• Avionics industry- a major multi-billion dollar industry
world wide
• Avionics equipment on a modern military or civil
aircraft\ account for around
– 30% to 40% of the total cost of the aircraft
airliner, maritime patrol/anti-submarine aircraft
(or helicopter)
– even Over 75% of the total cost in the case of an
airborne early warning aircraft
 Major driving force for avionics
• To meet the mission requirements with the minimum
flight crew
– crew salaries
– Expenses and training costs
– Reduction in weight-more passengers
– longer range with less fuel
– Increased safety
– Air traffic control requirements
– All weather operation
– Improved aircraft performance and control and
handling and reduction in maintenance costs
• Capability
• Reliability
• Maintainability
• Certificability
• Survivability(military)
• Availability
• Susceptibility
• vulnerability
• Life cycle cost(military) or cost of ownership(civil)
• Technical risk
• Weight & power
 Avionics system architecture
• Establishing the basic architecture is the most
fundamental challenge faced by the designer

• architecture must conform to the overall aircraft

mission and design while ensuring that the avionics
system meets its performance requirements

• architectures rely on the data buses for intra and

intersystem communications

• optimum architecture can only be selected after a

series of exhaustive design tradeoffs
Typical Avionics Architecture
 Evolution
Comm

Radar
NAV
Comm

Radar
NAV
Missi on

Missi on

Independent Avionics Federated Avionics

(40’s - 50’s) (60’s - 70’s)

Common Integrated
Processors
Common Digital
Common Analog Modules
ASDN Modules (Supercomputers)
Radar

Comm

EW

Integrated Avionics Advanced Integrated Avionics

(80’s - 90’s) (Post 2000)
 Pilot Vehicle
Interfacing

Integrated RF Sensing

Integrated
Core
Processing

Integrated EO Sensing

Integrated Vehicle
Management

Integrated Stores Management

Latest Cockpit
Serial communication
MIL 1553
 Elements of MIL
BUS CONTROLLER (BC)

REMOTE TERMINAL (RT)

MONITORING TERMINAL (MT)

TRANSMISSION MEDIA

multiple (commonly dual) redundant balanced

line physical layers, a differential) network interface, time
division multiplexing, half-duplex command/response
protocol, and can handle up to 30 Remote Terminals
(devices)
Transmission Media
Coupling
 Remote Terminals
Simple multiplex architecture

 “All terminals not operating as the bus controller or as a bus

monitor”
if it is not a controller, monitor, or the main bus or stub, it must
be a remote terminal
remote terminal comprises the electronics necessary to transfer
data between the data bus and the subsystem
Subsystem  user or sender of data
 Remote Terminals
• mainly to convert analog and discrete data to and from
a data format compatible with the data bus
• subsystems were still the sensor that provided the
data and computer, which used the data
• With new development in digital avionics, the trend
has been to embed the remote terminal into the
sensor and computer
• Today it is common for the subsystem to contain an
embedded remote terminal
• A remote terminal typically consists
– transceiver
– an encoder/decoder, a protocol controller,
– a buffer or memory, and a subsystem interface
Remote Terminal with subsystems
Typical system
 Bus Controller
• responsible for directing the flow of data on the data
bus
• several terminals may be capable of performing as the
bus controller, only one bus controller may be active at
a time
• the only one allowed to issue commands onto the data
bus
• commands may be for the transfer of data or the
control and management of the bus
• bus controller is a function that is contained within
– a mission computer
– a display processor
– a firecontrol computer
 Bus Controller
• Three types of architectures
– Word controller
– Message controller
– Frame controller

• Word Controller
– oldest and simplest type of controller
– Few word controllers are built today
– the terminal electronics transfers one word at a time to the
subsystem
– Message buffering and validation must be performed by the
subsystem (a burden on the subsystem due to the timing
requirements of the bus)
Bus Controller :Message Controller
– Current bus controllers are message controllers
– output a single message at a time, interfacing with the
computer only at the end of the message or perhaps when
an error occurs
– Some are capable of performing minor error processing
• transmitting once on the alternate data bus, before interrupting the
computer
• computer informs the interface electronics where the message exists
in memory and provides a control word
– For each message, the control word typically informs the
electronics
• message type (e.g., a RT-BC or RT-RT command)
• which bus to transfer the message
• where to read or write the data words in memory
• what to do if an error occurs
– control words are a function of the hardware design of the electronics
and aren’t standardized among bus controllers
 Frame Controller
• latest concept in bus controllers
• microprocessors and Application Specific Integrated
Circuits (ASIC's)
• capable of processing multiple messages in a
sequence defined by the host computer
• capable of performing some error processing as
defined by the message control word
• Frame processors are used to “off load” the
subsystem or host computer as much as possible
– interrupting only at the end of a series of messages
– when there is an error that it cannot handle
 Bus Monitor
• is a terminal that listens (monitors) to the exchange of
information on the data bus
• standard strictly defines how bus monitors may be
used
– may collect all the data from the bus or may collect selected
data
– information obtained by a bus monitor be used “for off-line
applications (e.g., flight test recording, maintenance
recording or mission analysis)
– provide the back-up bus controller sufficient information to
take over as the bus controller
– recorder for testing (while collecting data it is just a
recorder)
– terminal functioning as a back-up bus controller
 Terminal Hardware
• electronic hardware between a remote terminal, bus
controller, and bus monitor (almost same)
• transmitters/receivers and encoders/decoders to
format and transfer data
• All three elements have some level of subsystem
interface and data buffering
• primary difference lays in the protocol control logic and
often this just a different series of microcoded
instructions
• common to find 1553 hardware circuitry that is also
capable of functioning as all three devices
Electrical characteristics
Protocol : Word formats
Data Encoding
Message Transfer Formats
Message Transfer Formats :Broad casts
Multi bus on Aircraft
 About ARINC
• Aeronautical Radio, Incorporated (ARINC) Company
• Develops and operates systems and services to
ensure the efficiency
• Operation, and performance of the aviation and
travel industries
• Two major thrusts:
– Communications and information processing services for
the aviation and travel industry
– System engineering, development and integration for
government and industry
 What is ARINC 429 ?
• Defines how avionics equipment and systems
should communicate with each other
• Interconnected by wires in twisted pairs
• Defines the electrical and data characteristics and
protocols
• Employs a unidirectional data bus standard known
as Mark 33 Digital Information Transfer System
(DITS)
• Messages are transmitted at a bit rate of either
12.5 or 100 kilobits per second
• Transmission and reception is on separate ports
 ARINC 429 Usage
• Installed on most commercial transport aircraft
– A310/A320 and A330/A340;
– Bell Helicopters;
– Boeing 727, 737, 747, 757, and 767;
– McDonnell Douglas MD-11
• Unidirectional ARINC 429 system provides
– high reliability at the cost of wire weight
– limited data rates
 ARINC 429 Electrical Characteristics
• uses two signal wires to transmit 32 bit words
• Transmission of sequential words is separated by at
least 4 bit times of NULL (zero voltage)
• eliminates the need for a separate clock signal wire
, therefore known as a self-clocking signal
• nominal transmission voltage is 10 ±1 volts
between wires
• One wire is called the “A” (or “+” or “HI”) side and
the other is the “B” (or “-” or “LO”) side
• known as bipolar return-to zero (BPRZ) modulation
• The composite signal state may be one of three levels:
– HI which should measure between 7.25 and 11 volts
between the two wires (A to B)
– NULL which should be between 0.5 and -0.5 (A to B)
– LO which should be between -7.25 and -11 volts (A
to B)
• received voltage depends on line length and the
number of receivers connected to the bus.
• No more than 20 receivers should be connected to a
single bus.
• Since each bus is unidirectional, a system needs to
have its own transmit bus if it is required to respond or
to send messages
ARINC 429 Bit Encoding Example
Slew rate (rise and fall times) for 100k and 12.5k data rates
ARINC 429 Characteristic Summary
 Protocol
• point-to-point protocol
• only one transmitter on a wire pair
• transmitter is always transmitting either 32-bit
data words or the NULL state
• At-least one receiver on a wire pair
• message consists of a single data word
• Label field defines the type of data
 Bit Timing and Slew Rate
• slew rate refers to the rise and fall time of the
ARINC
• refers to the amount of time it takes the
ARINC signal to rise from the 10% to the 90%
voltage amplitude points on the leading and
trailing edges of the pulse
Slew Rates and Bit Timing Diagram
Bit Timing Diagram
 ARINC 429 Word Format
• data words are always 32 bits
• five primary fields, namely
– Label
– Source destination identifier - SDI
– Data
– Status Sign Matrix - SSM
– Parity
• convention numbers the bits from 1 (LSB) to 32
(MSB)
• Data types : BCD and BNR
Generalized ARINC Word Format
BCD
 Parity
• MSB is always the parity bit for ARINC 429
• Parity is normally set to odd except for certain
tests
• Odd parity means that there must be an odd
number of “1” bits in the 32-bit word
• if bits 1-31 contain an even number of “1” bits,
bit 32 must be set to create ODD parity
• if bits1-31 contain an odd number of “1” bits,
the parity bit must be clear
 Status Sing Matrix -SSM
• Bits 31 and 30 contain the Sign/Status Matrix or
SSM
• field contains
– hardware equipment condition
– operational mode, or validity of data content
SSM Codes for BCD data are given below:
• SSM Codes for BNR data are given below:
• Data
– Bits 29 through 11 contain the data, which may be
in a number of different formats

• SDI
– Bits 10 and 9 provide a Source/Destination
Identifier or SDI
– Used for multiple receivers to identify the receiver
for which the data is destined
– used in the case of multiple systems to identify
the source of the transmission
• Label
– Bits 8 through 1 contain a label identifying the data type
and the parameters associated with it
– used to determine the data type of the remainder of the
word

• Transmission Order
– The least significant bit of each byte except the label is
transmitted first
– the label is transmitted ahead of the data in each case
– order of the bits transmitted on the ARINC bus is as
follows:
8, 7, 6, 5, 4, 3, 2, 1, 9, 10, 11, 12, 13 … 32
 ARINC 429 Data Types
• The data type may be
– Binary Coded Decimal (BCD)
– two’s complement binary notation (BNR)
– Discrete Data
– Maintenance Data
– Acknowledgment
– ISO Alphabet#5 character data
 BCD Data Encoding
• four bits are allocated to each decimal digit
• Its data fields contain up to five sub-fields
• The most significant sub-field contains only the
bits, so that its maximum decimal value can be 7
• If the maximum decimal value is greater than 7,
bits 29 through 27 are padded with zeros
Generalized BCD Word Format

BCD Word Format Example

 BNR Data Encoding
• encoding simply stores the data as a binary
number
• Bit 29 is sign bit and bit 28 is MSB, which
represents one half of the maximum value of
the parameter being defined

Generalized BNR Word Format

• Negative numbers are encoded as the two’s
complement of positive values
• If bit 29 is a ‘1’ then the number is negative,
Otherwise, it is positive

Example BNR Encoding

 Mixed Formats
• 32-bit message words can also include discrete
information
• Either mixed with BCD or BNR data, or as
separate messages
• Unused bits in a word may be assigned one bit
per variable starting in Bit #11 until the data
field is reached.
• If there are no discrete encoded the word, the
unused positions are filled with zeros
Dedicated Discrete Example
Dedicated Discrete Example
contd
Data Translation Method

Examples of BCD Labels

Examples of BNR Labels
Equipment IDs
 Bit Oriented Protocols
• Protocol is a system for transferring files between
ARINC units
• source initiates communications by sending
certain predefined codes
• If a bit-oriented transfer is desired, the initial
code word will be an "ALO"(for Aloha) signal to
the potential recipient.
• When a source wants to transmit to a unit
– it sends a Request to Send word (RTS),
– and waits to receive a Clear to Send (CTS)
• Files are transferred in blocks called Link Data
Units (LDU) ranging in size from 3 to 255 words
• the source initiates a Version 1 transfer with a
Start of Transmission word (SOT)
• The SOT includes a
– file sequence number
– a General Format Identifier (GFI)
– a LDU Sequence Number
• The data words are then sent, followed by the (up
to) 255th word which is an End of Transmission
(EOT)
• Each LDU transfer (255 words or less) is
terminated by an End of Transmission Word
(EOT)
• The EOT includes a CRC and identifies the
position of the LDU in the overall file transfer
• The sink performs a verification process on the
EOT, and sends an Acknowledgment Word(ACK)
if all tests are passed
• The source then sends another CTS, and the
process is repeated until the last LDU is
acknowledged
File Transfer Scheme Version 1 (no Windows)
 ARINC 629
• the new Boeing 777 Aircraft
• uses a high-speed bi-directional bus
• capable of either periodic or aperiodic
transmissions
• Access to the bus is controlled by a sophisticated
protocol involving
– wait periods, quiet periods and other rules
Topology
Data bus
Data format
 Electronic display
•vital to the operation of any aircraft
• they provide information to the pilot (whether civil or
military)
Primary flight information
• Navigation information
• Engine data
• Airframe data
• Warning information
Military
•Infrared imaging sensors
• Radar
• Tactical mission data
• Weapon aiming
• Threat warnings
 Electronic display
• Pointers
• Indicators
• Reflective display
– Requires ambient light to be visible
• Emissive display
– Marker beacon, gear up/down

• LED
• plasma
Features of CRT
•Full colour
•Graphics display
•Good resolution
•Sunlight readable
•Dimmable
•Reasonably power efficient
•Electronic Display : Flexibility of providing any
indicator at any location
•Displays can be interchanged across captain and first
officer
EFIS (Electronic flight instrument
system) Primary Flight Display
Navigation Display
Flight management Computer
Control and Display Unit
 Display

• No mechanical parts (all glass cockpit)

• Resource sharing helps reducing the cost and
weight
– In case of displays the voltage level ranges from
few volts to kilo volts
– So a separate power supply, connectors ...are
better
• symbol generators are shared
– Alpha Numeric Characters, flight plan, radio
frequency characters .... Are same and common
Electronic Flight Instrument System
 Mandatory Parameters
 Time or relative time count Trailing edge flap or cockpit
 Pressure altitude control selection
Leading edge flap or cockpit
 Indicated airspeed control selection
 Heading Thrust reverser status
 Normal acceleration Ground spoiler position and/or
 Pitch attitude speed brake selection
 Roll attitude Total or outside air temperature
Autopilot and autothrottle mode
 Manual radio transmission and engagement status
keying Longitudinal acceleration (body
 Propulsive thrust/power on axis)
each engine and Lateral acceleration
thrust/power lever position Angle of attack
(if applicable)
Aircraft with an electronic flight instrument system (EFIS) are
required to have the additional parameters
• Selected barometric setting
• Selected altitude
• Selected speed
• Selected mach
• Selected vertical speed
• Selected heading
• Selected flight path
• Selected decision height
• EFIS display format
• Multi function/engine/alerts display format
 Classifying Instruments
•Flight Instruments
•Engine Instruments
•Navigation Instruments
 Electronic Instruments for Engine & Airframe
system control
• gas turbine engine
• indicate fuel flow
• temperature indicators
• engine speed in percentage of normal shaft speed (N1
and/or N2)

•reciprocating engine
• instruments generally indicate oil pressure and temperature
• cylinder head temperature
• exhaust gas temperature for one (usually the hottest-
running or sometimes all cylinders)
• absolute pressure
• Airframe  ”common definition”
– aeroplane structure excluding instruments and
engine

•Various sensors are needed for the monitoring and

control of airframe systems
•indications and/or control circuit need to be informed of
the position of a particular feature on the aircraft
•sensors detect one of two states or variable position
•Two state conditions
•landing gear or cabin door (micro switch/proximity
sensor)
•Variable positions
•flap position or control surfaces (synchros and
variable Resistors)
Landing Gear control system
Landing Gear control schematic
Flap control
 Flying control surfaces
leading edge slats
spoilers
trailing edge flaps
rudder(s)
elevators
ailerons
Airframe hydraulic parts
 Engine indicating and crew alerting system
(EICAS)
Electronic Centralized Aircraft Monitoring system
(ECAM)
• Engine Indication and Crew Alerting System (EICAS)
– Boeing developed system
– provides all engine instrumentation and crew annunciations
in an integrated format
• Electronic Centralized Aircraft Monitoring (ECAM)
system
– system used on Airbus aircraft (paperless cockpit)
• Two systems operate on different philosophies
– however their basic functions are to monitor aircraft systems
and display relevant information to the pilots
 EICAS and ECAM
• Both systems produce
– warning cautions and advisory messages that need to be
evaluated by the crew
– in certain cases, the system provides the procedures
required to address the problem

• ECAM provides the main features of EICAS but also

displays corrective action to be taken by the crew as
well as system limitations after the failures
•aircraft sensors are categorized
into key monitoring functions
•these sensors transmit data
into two system data acquisition
concentrators (SDAC)
•data is processed and supplied
into flight warning computers
(FWC)

FWCs are programmed to

identify any inconsistencies in
the data and then output the
data through three display
management computers (DMC)
• system fault or event is detected
– one of the FWCs generates the appropriate
warning messages and aural alerts
– Critical systems such as engine and fuel quantity
are routed directly into the FWCs so that they can
still be monitored in the event of both SDACs failing
• ECAM can tolerate the a failure of one SDAC and
one FWC and still continue to operate
• Level 3 failures – red
warnings:
• situations that require
immediate crew action
• indicate that the aircraft is in
danger
• Examples
– engine fire
– loss of cabin pressure
• Level 3 system failures
illuminate the red master
warning light,
– a warning (red) ECAM message
and an aural warning
– can be a continuous repetitive
chime, a specific sound or a
synthetic voice
• Level 2 failures – amber cautions:
– situations that require crew attention but not immediate
action
• Examples
– Bleed air failure or a fuel system fault
• Level 2 failures have no immediate or direct impact
on flight safety
– cautions are displayed to the crew by an amber master
caution light
– an amber ECAM message and a single chime
• Level 1 failures
– these are system failures and/or faults that
could lead to a loss of system redundancy
– require monitoring but have no immediate
impact on continued safe operation of the
aircraft
• Examples of level 1 failures include
– loss of a fuel system temperature sensor
• Level 1 failures are displayed to the crew by amber
ECAM messages only (no aural warning).
A simplified EFIS
 ECAM

displays aircraft system status, checklists, advisories, and

warnings on a pair of controllable monitors
ECAM Control Panel
EICAS
EICAS Control Panel
 Autothrottle system
• A system that automatically manipulates the thrust setting of the airplane to
help follow the vertical trajectory portion or selected airspeed of the planned
flight route????

controls the speed of the aircraft by adjusting the position of the

throttles
ensures that the maximum fuel efficiency is obtained by the
engines during all stages of flight
 Autothrottle
• thrust management computer (TMC) receives data
from various systems
• computes the information that will effect the operation
of the autothrottle system
• sends the information to the servo units in the
autothrottle system to drive the throttles to a selected
position
• TMC receives information from the engine & aircraft
sensors to null any movement of the thrust levers
once the desired speed has been achieved
 Autothrottle
• 2 modes of operation
• Speed mode :
– which controls the speed of the aircraft
– is used during climb, cruise & landing stages only
• EPR mode :
– controls the engine pressure ratio (EPR) during the take-
off stage of the aircraft
– due to air conditioning & pneumatic systems, a
reduction in thrust occurs
– these losses are called engine bleeds
– TMC uses this information to calculate the losses due to
the bleed extraction and to compensate these losses
Autopilot Systems