Airbus Flight Control System

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Explains how redundancy and diversity are used in the flight control systems of the Airbus 330/340 to achieve safety and reliability

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Airbus Flight Control System

  1. 1. The Airbus flight control system Ian Sommerville Airbus Flight Control System, 2013 Slide 1
  2. 2. • The organisation of the Airbus A330/340 flight control system to provide software and hardware reliability Airbus Flight Control System, 2013 Slide 2
  3. 3. Airbus Flight Control System, 2013 Slide 3
  4. 4. Airbus flight control systems • Airbus were the first commercial aircraft manufacturer to use „fly by wire‟ flight control systems Airbus Flight Control System, 2013 Slide 4
  5. 5. “Fly by wire” control • Older aircraft control systems rely on mechanical and hydraulic links between the aircraft‟s controls and the flight surfaces on the wings and tail. • The cockpit controls and flight surfaces are directly connected – pilot actions are transmitted directly to the control system Airbus Flight Control System, 2013 Slide 5
  6. 6. Airbus Flight Control System, 2013 Slide 6
  7. 7. • In fly-by-wire systems, the cockpit controls generate electronic signals that are interpreted by a computer system and are then converted into outputs that drive the hydraulic system connected to the flight surfaces. Airbus Flight Control System, 2013 Slide 7
  8. 8. Advantages of „fly-by-wire‟ • Weight reduction – By reducing the mechanical linkages and hydraulic fluids, a significant amount of weight (and hence fuel) is saved. Airbus Flight Control System, 2013 Slide 8
  9. 9. • Pilot workload reduction – The fly-by-wire system provides a more usable interface and takes over some computations that previously would have to be carried out by the pilots. Airbus Flight Control System, 2013 Slide 9
  10. 10. • Airframe safety – By mediating the control commands, the system can ensure that the pilot cannot put the aircraft into a state that stresses the airframe or stalls the aircraft. Airbus Flight Control System, 2013 Slide 10
  11. 11. Fault tolerance • Fly-by-wire systems must be fault tolerant as there is no „fail-safe‟ state when the aircraft is in operation. • In the Airbus, this is achieved by replicating sensors, computers and actuators and providing „graceful degradation‟ in the event of a system failure. • In a degraded state, essential facilities remain available allowing the pilot to fly and land the plane. Airbus Flight Control System, 2013 Slide 11
  12. 12. • The Airbus FCS has quintuple redundancy i.e it has 5 flight control computers but only 1 computer is needed to fly the place • Therefore, the system can stand to lose 4 computers and the plane will still be flyable. Airbus Flight Control System, 2013 Slide 12
  13. 13. Airbus FCS organization • Three primary flight control computers • These are the main flight control systems and are responsible for calculations concerned with aircraft control and with sending signals to the flight surfaces and aircraft engines. Airbus Flight Control System, 2013 Slide 13
  14. 14. • Two secondary flight control computers which are backup systems for the flight control computers. • Control switches automatically to these systems if the primary computers are unavailable. Airbus Flight Control System, 2013 Slide 14
  15. 15. Hardware diversity • The primary and secondary flight control computers use different processors. • The primary and secondary flight control computers are designed and supplied by different companies. • The processor chips for the different computers are supplied by different manufacturers. • All of this reduces the probability of common errors in the hardware causing system failure. Airbus Flight Control System, 2013 Slide 15
  16. 16. Software diversity • The primary and secondary computers run different software • The secondary computer software is a simpler version of the primary control software • The software for each system has been developed by different teams Airbus Flight Control System, 2013 Slide 16
  17. 17. Self-monitoring architecture Airbus Flight Control System, 2013 Slide 17
  18. 18. Self-monitoring architectures • Multi-channel architectures where the system monitors its own operations and takes action if inconsistencies are detected. • The same computation is carried out on each channel and the results are compared. If the results are identical and are produced at the same time, then it is assumed that the system is operating correctly. • If the results are different, then a failure is assumed and a failure exception is raised. Airbus Flight Control System, 2013 Slide 18
  19. 19. Self-monitoring systems • Hardware in each channel has to be diverse so that common mode hardware failure will not lead to each channel producing the same results. • Software in each channel must also be diverse, otherwise the same software error would affect each channel. • If high-availability is required, you may use several self-checking systems in parallel. – This is the approach used in the Airbus family of aircraft for 19 Slide Airbus Flight Control System, 2013
  20. 20. Airbus Flight Control System, 2013 Slide 20
  21. 21. Channel diversity • The software for the different channels in each computer has been developed by different teams using different programming languages Airbus Flight Control System, 2013 Slide 21
  22. 22. Primary/secondary diversity • The software for the primary and secondary flight control computers has been developed by different teams. • For the secondary computers, the channels are programmed by different teams using different languages. • Therefore, 4 different versions of the flight control software have been developed. Airbus Flight Control System, 2013 Slide 22
  23. 23. Dynamic reconfiguration • The FCS reconfigures itself dynamically to cope with a loss of system resources if 2 FCS computers fail • Dynamic reconfiguration involves switching to a simpler mode of software control, with less to go wrong. • Three operational modes are supported – Normal - control plus reduction of workload – Alternate - minimal computer-mediated control – Direct - no computer-mediation of pilot commands Airbus Flight Control System, 2013 Slide 23
  24. 24. Control diversity • The linkages between the flight control computers and the flight surfaces are arranged so that each surface is controlled by multiple independent actuators. • Each actuator is controlled by different computers so loss of a single actuator or computer will not mean loss of control of that surface. • The hydraulic system is 3-way replicated and these take different routes through the plane. Airbus Flight Control System, 2013 Slide 24
  25. 25. Summary • Airbus FCS designed around hardware and software redundancy and diversity • Quintuple redundancy with 5 control computers – only one required to fly aircraft • Each computer based on a self-monitoring architecture with 2 channels • Multiple different versions of software developed and execute simultaneously Airbus Flight Control System, 2013 Slide 25

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