Systems design and integration Flashcards
Identify electronic systems on aircraft
sensors(air data,inertial sensors,radars) displays(HUDs,HMDs,HDDs) communication systems navigation systems(VOR/DME,GPS,INS) flight control systems(FBW) autopilot and flight management systems system integration(data bus technology)
Overview of avionics systems
Evolution of avionics
distributed analog, distributed digital,federated digital, integrated modular
Describe distributed analog
simplex point to point wiring single source-single sink
Describe distributed digital
simple point to point wiring single source-multi sink
Describe federated digital
half duplex data bus and stubs multiple source-multiple sink command/response multiplex data bus dedicated computational modules
Describe integrated modular
full duplex switched ethernet/full duplex data bus and switches interdependent computational modules multiple source-multiple sink
System design factors
mission safety-certification requirements required functionality reliability integration maintenance cost constraints(mass,space) operational stability
Certification considerations
CS23 for small aircraft CS25 for large turbine transport category aircraft FAR part23 and FAR part25
Define EASA CS23
seating configuration(excluding pilot seats) of 9 or fewer MTOM of 5670kg(12,500lb) or less propeller driven twin engine aircraft seating configuration(excluding pilot seats) of 19 or fewer MTOM of 8618kg(19,000lb) or less
Define EASA CS25
jet powered aircraft with 10 seats or more MTOM greater than 5670kg(12500lb)
Differences between FAR part 25 and CS25
performance criteria e.g. climb gradient performance system redundancy requirements e.g, more robust stall protection systems safety equipment e.g. FDR and CVR
CS25 system safety criteria/assessment
airworthiness requirements an inverse relationship exists between the probability of the occurrence(per flight hour) and the acceptable degree(severity) of hazard
Below the line is the acceptable range
Basic design process(safety)
FHA - FTA- FMEA
Product reliability curve
Management system design considerations
failure analysis
system management logic
crew role and crew interface
redundancy requirement/type
system integration
Redundancy techniques
- modular redundancy with voting(active hot)
- dynamic redundancy(active hot and active cold)
Modular redundacy with voting(active hot)
- all redundant systems are active
- during a malfunction or unreliable input, the control system identifies and isolates the unreliable system
- energy required to keep the system online and complex control
- used in flight control situations
Dynamic redundacy(active warm)
- only the output of the active system is used
- requires energy to keep all system running
- when the active system fails, the switch to the redundancy is quick(with some lag)
Dynamic redundancy(active cold)
- only one system running/active
- failure of an active system starts redundant system and brings it online
- start and run up lag means lack of output continuity(saves energy)
Benefits of integration
- allows for enhanced safety provision
- appropriate reduction in crew workload
- more economic operation of system
Distributed analogue architecture
- disjointed point solutions to control individual aircraft system functions
- electronics implemented in analogue with a considerable amount of hardwired aircraft wiring
- difficult to modify and upgrade
Digital networks
- high efficiency and integrity
- low latency/lag
- adaptability
- low mass and space
Define a data bus
a communication system that transfers data between different users
hardware-twisted pair of wire, fibre optic
software-communication protocol
employs time/frequency division multiplexing techniques
Define simplex
send only
e.g. radio broadcast
Define half duplex
send and receive but not at the same time
e.g. radio communications
Define full duplex
send and receive at the same time
e.g. telephone
Main characteristics of a distributed digital architecture
- single source,single sink
- single source,multisink
- industry-standard ARINC 429
Describe single source,single sink
- used dedicated links from one transmitting unit to one receiving unit
- major functional unit contain their own digital computer and memory
- allows data to be passed in digital form between major processing centres on the aircraft
- undirectional, point to point, simplex
- considerable wiring required
- point to point for each connection
- complexity, weight and difficult to upgrade
Describe single source, multiple sink
- enables simplified wiring and weight saving
- standard ARINC 429
- data transfer standard for avionics promoting interoperability between devices on civil aircraft
- a unidirectional point-to-multi-point serial data bus
- simplex
- originally intended for repetitive data
Federated digital architecture
- multi-source,multi-sink architecture
- half-duplex
- industry standards
- ARINC 629
- MIL-STD 1553B
Multi-source,multi-sink
- a single bus is used to transmit and receive information(1-2Mbps)
- half-duplex
- bidirectional multi-drop capacity
- dedicated LRU’s and subsystems have their own processor, memory and power supplied but with improved data sharing
Why are data buses federated?
to reduce data bus loading and preserve bandwidth
systems partitioned by data bus allow like-minded systems to share data
inter-bus links exist to link buses
MIL-STD 1553B
intended for repetitive data
dual redundant data(2 twisted pairs of wire)
data is separated using time-division multiplexing
simultaneous transmission by multiple devices
ARINC 629
- intended to work with A429, reducing wiring, complexity and allow transfer of non-periodic data
- redundancy of devices supported but not for cables
- each transmission has a cable indicating the type of data being sent
- the processor can either process or ignore the message
Advantages and disadvantages of multi-source,multi-sink
Advantages
- less wiring
- allows for easier equipment change and configuration
Disadvantages
- separate processing and infrastructure for each component or subsystem
- limited intercommunication
- application-specific Line replaceable Units
- difficult to upgrade
- insufficient data bus technology with many wires
- limited rate
- high cost for A629 devices due to very small competitive market
Factors leading to change
Data explosion
- sensor data fusion
- performance-based navigation
- quantity of data needed to be processed on-board
COTS (commercial off the shelf) technologies
- internet network protocol
- ethernet
Obsolescence
Integrated Modular Architecture
- multi-source,multi-sink
- full-duplex
- AFDX -aviation full duplex
- industry-standard
- ARINC 664 pt 7
- more centralised and shared computing facilities
- LRM within cabinets, more efficient
- easy to upgrade
- reduced mass, power and space
- increased reliability
ARINC 664 pt 7
- addresses the limitations of A429/629
- enables ethernet and switching and COTS applications
- high data transfer rates 100Mbps
- full-duplex bidirectional communications
- high data integrity/redundancy
- reduced costs
- application software certified independently of the IMA hardware platform
- physical links replaced with virtual links with bounded latency and guaranteed bandwidth
- many multiplexed onto a single wire connection
Importance of application software being certified independently of the hardware
allows upgrading
obsolescence protection for the hardware
.First generation IMA
avionics subsystem implement by a single supplier
the supplier uses their own standards, modules and paralleled backplane
Second generation IMA
open architecture with multiple supplier modules
applications hosted in a standard backplane
application supplier certifies the application/hardware combination and supplies the module on which the application is hosted to the airframe manufacturer
Third generation IMA
independent provision of open-architecture modules and applications
applications run under an open standard real-time DS
a single module may have multiple applications
integration and certification is the system integrator’s responsibility
