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autonomous operation through hot back-up, selective
triplication, and redundant data storage
11
Generic Aircraft Fault Handling Approaches
Physical and spatial redundancy – multiple copies
geographically distributed
Redundant Paths - for example, different jet engines drive
redundant electrical generators which power two independent
computers that in turn drive different hydraulic systems for
controlling different flight surfaces
Functional Redundancy – if both generators fail, batteries
provide power until a ram air turbine can be deployed
Architectural Migration – from mechanical flight control to
parallel mechanical/electronic to all electronic “fly by wire”
Tolerate Expanding Fault Classes – component failure,
power failure, object impact, electromagnetic interference,
cloud environment, Byzantine faults, design errors
12
Generic Avionics Architecture
Pilot Interface EFCS
Sensors
Actuators
Flight
Control
Surfaces
commands commands
status status
sensory
outputs
control
signals
position
translation/
rotation
Electronic
Flight
Control
System
13
Fault Tolerant Mechanism for Space/Aircraft
Triple-triple modular redundancy for the
primary flight computers
Goal to handle Byzantine failures, commonmode
and common-area failures
Physical and electrical isolation of replicas
Code written in Ada
ARINC 629 bus
Dissimilar multiprocessors
Boeing 777 - flight
control computer
Design diversity emphasized to handle
common-mode & common-area failures
Two different processors (PRIM
and SEC)
Airbus A340 – flight 1993
control computer
Selective (not full) redundancy
Complete environmental testing
Adoption of vendor’s QA practices
Based on short mission duration, budget cap
and extreme thermal/landing conditions
$280 M
175,000 lines of code
32-bit RSC-6000 processor
128MB DRAM, VME backplane
VxWorks real-time OS
Object-oriented design (in C)
“Point-to-point” 1553B Bus
Mars Pathfinder 1996-1997
- Mars lander and
rover
No single point of failure
Primary/backup redundancy
Priority-based one-at-a-time handling of
multiple simultaneous faults
$3.26 B
32,000 lines of code
Code written in Ada
MIL-STD-1553B Bus (internal
redundant bus media)
Cassini-Huygens - 1997-2005
Saturn orbiter and
probe
Active/standby block redundancy,
microprocessor multicomputer
Galileo – Jupiter 1989 8000 lines of code
orbiter & probe
Active/standby block redundancy as
command/monitor pair
Voyager – outer planet 1977-1989 3000 lines of code
flyby
Configuration Fault-tolerance mechanisms
(Software, Hardware)
Mission/System Inception
14
Size of Software in Spacecraft Missions
1
10
100
1000
10000
100000
1000000
Lines of Code 30 3000 8000 32000 175000 600000
Mariner Voyager Galileo Cassini Pathfinder MER
15
Observations and Trends
Commercial off-the-shelf components – increasing use of
commercial standards and components to decrease design time and
cost. Accommodations for unique environment and safety issues.
Other issues include obsolescence, updates, integration, validation, and
adequate technical support.
Autonomy and fly-by-wire software – digital control of aircraft and
increasing autonomy of spacecraft under software control
Escalating fault sources and evolving redundancy – evolved from
basic command/monitor pair to triplication/median pick voting to
command/monitor redundancy. Design diversity to tolerate design
flaws. Spacecraft focus on availability and longevity while aircraft
focus on safety and dependability
Safing – historically spacecraft incorporates safing which may no
longer be effective for critical flight phases and autonomous operation
Deadlines – both spacecraft and aircraft systems have “shipping date”
deadlines dictated by planetary physics and financial consequences
MRO Headed for Record
Ameco Beijing just completed its 1,000th heavy maintenance project, a PW4000-powered Boeing 747-400.
Pratt & Whitney is accelerating its investment in MRO as it looks
to this sector to generate double-digit growth for the company.
New services, creative solutions, new repair technologies—and
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