1. Fault Tolerance Techniques of The Boeing 777
Samuel Hishmeh
December 6th, 2006

2. Fault Tolerance Techniques of the Boeing 777
Background
Boeing to Develop “Fly-By-Wire”
Fly-By-Wire Advantages
Safer
Cheaper
Revolutionized Flight
Developed in the early 90’s Boeing wanted to develop a fly-by-wire plane, One of first.
Fly-by-wire design several advantages
Potentially safer (human error), could you trust your life to a computer?
Cheaper (less upkeep, less weight (materials and gas) )
Fault Tolerance Techniques of the Boeing 777

3. Design Considerations
Cosmic Rays
Hardware Failures
“Fly-By-Wire” Functional Separation
No Single Fault can Cause Failure
The likelihood that cosmic rays will interfere with communication greatly increases at high altitudes
Fault Tolerance Techniques of the Boeing 777

4. Fault Tolerance Techniques of the Boeing 777
Design Philosophy
REDUNDANCY
Triple Modular Redundancy (TMR)
Computing System
Electrical Power
Hydraulic Power
Communication Path
4 Modular Redundancy
Actuator Control Electronics Unit (ACE)
TMR in used in hardware
SAFETY CRITICAL AVIONICS FOR THE 777 PRIMARY FLIGHT CONTROLS SYSTEM
Fault Tolerance Techniques of the Boeing 777

5. Flight Control Surfaces
Fault Tolerance Techniques of the Boeing 777

6. Fault Tolerance Techniques of the Boeing 777
TMR on data buses.
4MR on ACES – Actuator Control Electronics
Fault Tolerance Techniques of the Boeing 777

7. Primary Flight Computer
3 processors. Each had 3 lanes computing the result, and they can communicate. Despite access to all 3, the only output to one channel.
All code written in ADA, but compiled with different compilers.
Fault Tolerance Techniques of the Boeing 777

8. Fault Tolerance Techniques of the Boeing 777
ACE Hardware
Fault Tolerance Techniques of the Boeing 777

9. Fault Tolerance Techniques of the Boeing 777
Communication Bus
ARINC 629
Line Replaceable Units (LRU)
Triple Modular Redundancy
CRC Checking
Asynchronous Serial
2 MHz
Physical and Electrical Isolation
Developed by Boeing
Up 120 devices
Fault Tolerance Techniques of the Boeing 777

10. Fault Tolerance Techniques of the Boeing 777
Communication Bus [2]
Fault Tolerance Techniques of the Boeing 777

11. Fault Tolerance Techniques of the Boeing 777
Flight Modes
3 Modes
Direct
Secondary
Normal
Normal – Autopilot
Secondary – somewhere in between normal and direct. PFC still using some calculations, but not autopilot
Direct – Switch on or if ACE’s detect invalid data from PFC’s. Pilot has full control. Analog data from transducers used to control actuators.
Fault Tolerance Techniques of the Boeing 777

12. Fault Tolerance Techniques of the Boeing 777
Honorable Mentions
Deferred Maintenance
Electrical Isolation
CRC Checks
Line Replaceable Units (LRU)
Electrical isolation - every piece of hardware has multiple power systems.
Fault Tolerance Techniques of the Boeing 777

13. Fault Tolerance Techniques of the Boeing 777
Questions…
Fault Tolerance Techniques of the Boeing 777

14. Fault Tolerance Techniques of the Boeing 777
References
Y. Yeh. Triple-triple redundant 777 primary flight computer. In Proceedings of the 1996 IEEE Aerospace Applications Conference, volume 1, pages 293–307, February 1996.
Y.Yeh. SAFETY CRITICAL AVIONICS FOR THE 777 PRIMARY FLIGHT CONTROLS SYSTEM. In Digital Avionics Systems, DASC. The 20th Conference, Volume 1, pages 1C2/1-1C2/11, October 2001.
Fault Tolerance Techniques of the Boeing 777

15. Fault Tolerance Techniques of the Boeing 777
CRC Diagram
Fault Tolerance Techniques of the Boeing 777