Performance must be considered when evaluating Fail Operational The airplane which could have an effect on touchdown or rollout Of single components of the system, airplane or equipment external to Operating elements of the Fail Operational system. Or approach, flare, touchdown and rollout by using the remaining A Fail Operational System is a system which after failure of any singleĬomponent, is capable of completing an approach, flare and touchdown, Fail Operational Category III Operations. From the document we find for Fail Operational:Ĥ.3.2. That both A/Ps disconnect with minimal airplane maneuvering and withīoeing 737 FCOM volume 2 - Automatic Flight - System Descriptionĭefinitions provided by the FAA can be found in AC 120-28D - Criteria for Approval of Category III Weather Minima for Takeoff, Landing, and Rollout. If a failure occurs in oneĪ/P, the failed channel is counteracted by the second channel such If a failure is detected, the flight controls respond to the A/PĬommanding the lesser control movement. It implements fail operational on the inertial sources but fail passive on the autopilots. The Boeing 737 has 3 inertial sources but only 2 autopilots. Path or attitude, bu the landing is not completed automaticallyĪ320 FCOM - Procedures - Normal Procedures - Landing Categories There is no significant out-of-trim condition or deviation of flight While a "CAT 3 SINGLE" landing is fail passive: The remaining part of the automatic system allows the aircraft to (A320 FCOM - Aircraft Systems - Auto Flight - General)īut the FCOM does state a "CAT 3 DUAL" automatic landing is fail operational The FCOM does not detail how it does that. For example, the Flight Management and Guidance System (FMGS) on the Airbus A320 can switch from "Dual Mode" to "Single Mode". That is how fail operational can be implemented with two autopilots. Now here comes the interesting part: what if I can distinguish a failed unit from a functional unit, without using another functional unit? In other words, what if I have something that can monitor the existing units, but is incapable of functioning the same as one of the monitored units on its own? In a system of two, it is uncertain which one has failed, so all units come offline. In a system of three, a failure can be detected if one disagrees with the other two. It will say "LAND 3" or "LAND 2" respectively. Let's take the Boeing 777 because it is easy to begin with. The exact number of autopilots required to make this work, however, is debatable and much depends on how you define it. The reliability of the designed onboard computer is evaluated analytically, which indicates that the proposed OBC can meet the reliability requirements.The quoted explanation about "fail operational" and "fail passive" is correct, in that "fail operational" means the system will continue to function after an failure, and "fail passive" means the system will not misbehave after an failure. The case study shows that the similar architecture is used for high reliable flight computer of passenger airplanes except that our architecture is based on the available multicore microcontrollers.
All of the constituent modules of OBC, comprising processing unit, bus interface, sensor, actuators, and IO devices, benefits from triple redundancy. Thereafter, the results are applied to the system by actuators.TMR technology in component level is used to improve the reliability of OBC according to the system requirements. According to the acquired data, mission scenario and control algorithm are processed by the processing unit. In the proposed architecture, control inputs and system states are measured using designated sensors. In this paper, we concerned with the triple modular redundancy (TMR) for an onboard computer with aerospace application. To meet the reliability requirements for onboard computers, various type of redundancy must be employed. The control algorithm is processed by onboard computer (OBC). The flight control system must meet extremely high levels of functional integrity and availability.
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