Boeing Company Critical Analysis
Fly by Wire (FBW) system was used for the Boeing 777 flight control system. The 777 is the first commercial aircraft which was built by Boeing. The changes were very dramatic and encompassed many areas, including technical, organizational and administrative changes. It was the first 100% digitally designed and assembled airplane made by Boeing. Concurrent engineering, the concept of “Working Together”, was new philosophy to them. The team included design, manufacturing, customer and supplier personnel to pursuit same goal. Is this Fly by Wire (FBW) system new technology?
The answer is no. The electronic control systems have been used in commercial aviation for more than 40 years. The first commercial aircraft to use electronic control system was the Concord. It was used to manipulate the hydraulic system with mechanical backups. Europeans have now used FBW systems for more than four decades; however the United States was technologically backward from Europe’s. In October 1990, the Boeing Company initiated the Boeing 777 project a first-time experience to build a totally FBW controlled aircraft and completely designed and integrated by computer technology.
Not only had this aircraft created great challenges in the technological area but also in the managerial area, to ensure the success of the project. This fully FBY system was a challenge for systems engineering but it was an advantageous and beneficial system. 1. FBY system overview Function of FBY system is different from fly by cable system. Computers control electric and electro hydraulic actuator by electrically transmitted commands which, input through conventional line such as wheel, rudder pedal, and speed brake lever, provide automatic or manual to the aircraft pitch, yaw, and roll axis.
Multiple position transducers mounted on each pilot controller sense the pilot commands for Actuator Control electronics units. The FBY technology offers significant benefits for pilots as well as maintenance technicians. Conventional primary flight control uses hydraulic actuators and control valves controlled by cables are driven by the pilot controls. The cable-controlled system typically is heavy and requires periodic maintenance; however in FBW system the actuator was controlled electronic signal so cable control surface was removed.
The FBW offered potential weight savings by permitting use of a relaxed static stability aerodynamic configuration and making it possible to put up few derivative models with minimum of change. The 777 primary flight controls (PFC) is highly redundant digital computer providing most of system management. Full time surface control utilizes sophisticated control laws. The aerodynamic surfaces of the 777 have been sized to afford the required airplane response during critical flight conditions. The reaction time of the control laws is much faster than an alert pilot.
Thus the size of the flight control surfaces could be made smaller than those required for a conventional control aircraft. 2. Triple redundant system Some of the demanding performance requirements are that a particular component becomes in-operative and results in some particular element remaining active but its functionality is in error. A fault-tolerant system normally uses both hardware and software. This system is called “Triple-triple redundancy”. It has the capability for automatic and dynamic reconfiguration of the system.
In order to deal with it, different levels of redundancy are used: depending on the level of criticality, it depends on the acceptable probability of failure and probability. This system covers all hardware and software elements. There are three PFCs in the Primary Flight Control System (PFCS), each with three identical computing units within each PFC. So the consequence is that it provides nine identical computing channels. Even if any of the three PFCs fails totally and affect other computing lanes, the PFC loses no functionality.
Triple-triple redundancy becomes significantly important during critical flight situations. It is the ability of a system to continue safe operation in the presence of one or more simultaneously happening hardware or software faults. It is a term that is used to define the ability of any system to withstand a single or multiple failures which results in either no loss of functionality, a known loss of functionality or reduced level of redundancy while maintaining the required level of safety. In case of the 777, software was used instead of using hardware to achieve fault tolerance in analytical redundancy.
In case of faulty sensor, the triple redundancy system gathers data from the remaining functioning sensors with data from other sources in the aircraft to compute the most probable value from the failed sensor. This computed value is used in the same way as a value from a functioning sensor. Once the systems analyze the degree of fault tolerance required in the system, the system can relapse to replication or to the duplication and comparison modes of operation. The failed processor then executes self-diagnostic check and, if no permanent faults are found, returns active status. 3.
Primary flight control system The PFCS is controlled electronically, there is an opportunity to include system control augmentation and cover protection features that would have been difficult to provide in a conventional mechanical system. The 777 PFCS was made with full use of the capabilities of this design by including bank angle protection, turn compensation, stall and over-speed protection pitch control and stability augmentation thrust asymmetry compensation. The Actuator Control Electronics (ACE) provides the interfaces with all the analog sensors and analog-digital conversion of signals to the PFC.
ACE, actuators, hydraulics, and electrical signaling are distributed such that the airplane is safely controllable with loss of any two channels. The FBW system is the most critical system in the airplane so it is important for early detection of system failure and to protect it from all the other systems by separating it as much as possible from the rest of the equipment. Dedicated electric power is provided and permanent magnet generator is mounted on each engine shaft so DC power supply assemble (PSA) feeds each channel of the FBW system.
In addition, alternate sources of power are provided to the PSA from the 28 volt DC bus, battery bus and the ram air turbine, which also supplies emergency hydraulic power in even of separating from other equipment. Not only these protections are used to separate from redundant parts but also a dedicated set of ARNIC 629 is used which limits access to only those signals required by the FBW system. The FBW system is such a sophisticated and critical element of the aircraft; it is separate from redundant part such as computer and hydraulic lines thus protecting against damage in case of engine and landing gear failures.
4. Cockpit The other consideration was that even though the highest technology was used to develop the aircraft, pilot is the one to operate aircraft, so cockpit is next key decision. Cockpit control system should be familiar to pilot because most of those pilots would be transitioning from other Boeing aircraft. It was also considered important that automatic controls such as auto pilot and auto throttle functions should still be easy to monitor.
There are few safety features included to prevent unintentional exceed of operational limitations: Over speed and under speed protection, bank angle, and engine thrust irregularity from takeoff taxi through landing rollout. The phrase protection is chosen purposely which provide final authority to the pilots. If the pilot wants to go beyond the value which the protection function applied, the pilot could apply considerable extra force to effect further change. This is considered important because it is difficult to anticipate all eventualities that may occur, so all options should remain open for the pilots.
While some of these features added complexity, both in hardware and software, they have proven popular in service. 5. Test In order to provide the required validation test coverage a number of laboratory facilities were used to provide proof of system reliability. System Level integration testing was performed at the 777 Flight controls Test Rig (FCTR), Systems Integration Lab (SIL), and an Engineering Simulator Cab (Cab2). The FCTR was primarily used by flight controls and hydraulics for system level tests, and the SIL and Cab 2 were primarily use for airplane level validation with some flight controls validation when appropriate.
Also compliance testing was also the most enviable method. Analysis is used to validate system performance, safety predictions and reliability based on system redundancy. Similarity was also used as a method of validation when the system achievement was identical with previous system confirmed satisfactory performance; however this method should never be used by itself. There must be evidence to show that previous system meets the current system requirement. Inspection is used as method when document or review of installation is available.
In addition, supplier should perform a variety of test and analysis to prove that their design meets requirement. Perhaps all the systems became more interdependent and complex: it therefore became very important for every department to pursue same goal ensure that all bases were covered. One team called “Multi Functional System Requirements Team” were established to assemble all requirements for the FCS function, performance, reliability, safety, crew operation and maintenance.
One of the most useful combination tools proved to be an Issue Tracking and Compliance System that allowed all problems and issues to be recorded and progress toward resolution was tracked and available to management and to all team members for information and comment. Many of the processes utilized in the 777 program have since been formally documented in SAE ARPS 4754 and 4761 which provide Guidelines for the Development of Complex Systems. 6. Conclusion However FBW system was not new technology, the Boeing777 FBW system develop new technology in the form of a complete FBY system.
It was significantly better than the old system in areas of control characteristic and reduction of aircraft weight. At the same time, cockpit remains similar to old version to prevent any confusion for pilots who transfer from other type of Boeing aircraft. This saves some money for Airline Companies. Establishing Multi Functional System Requirements Team was a very smart idea because not only engineering department but also safety, crew maintenance and other departments pursued same goal to analyse any difficulty.?
The system is useful to the company and supplier and maybe to customer. This is actually what we have to do in our society to solve issues that we encounter. This proves that if we work together as a team we can do it. Among the all the factor the Boeing is accomplished this Boeing 777 project. . ? Reference 1) Miguel A. Ayala, “Boeing 777 Flight control system” 2) Jim McWha, “Development of the 777 flight control system” AIAA Guidance, Navigation, and Control Conference and Exhibit11-14 August 2003, 3) Y. C (Bob) Yeh “Triple-triple Redundant 777
Primary Computer system”, Boeing Commercial Airplane Group. 4) Chris Fielding “The design of Fly-By-Wire Flight Control System. 5) Matt Lave “Fly by wire on Boeing 777”. fly-by-wire. freeservers. com/ 6) Saurabh Chheda “The Boeing 777” http://euler. ecs. umass. edu/ 7) Local Air Safety Chairman, Delta Council 16 “A Primer for Aviation accident Investigator. ” Air Line Pilot, February 2000 8) Boeing 777 http://www. cds. caltech. edu/conferences/1997/vecs/tutorial/Examples/Cases/777. htm
