Return to article

 
777 FLY-BY-WIRE MAINTENANCE

The flight control system for the 777 airplane is different from those on other Boeing airplane designs. Rather than have the airplane rely on cables to move the ailerons, elevator, and rudder, Boeing designed the 777 with fly-by-wire technology. As a result, the 777 uses wires to carry electrical signals from the pilot control wheel, column, and pedals to a primary flight computer (PFC). The PFC combines these pilot inputs with inertial data and air data from the air data inertial reference system to produce flight control surface commands. The PFC then sends the commands, also in the form of electrical signals carried by wires, to the actuator control electronics, which in turn control the hydraulic actuators that move the control surfaces. Though the 777 does not have direct cable connections from the pilot controllers to the hydraulic actuators for most surfaces, for redundancy it has a cable control path from the wheel to one pair of flight spoilers and a redundant cable control input to the stabilizer.

The 777 fly-by-wire flight control system provides all functions necessary for manual control of the airplane in the pitch, roll, and yaw axes. The PFC control laws provide basic maneuver control, stability augmentation, and envelope protection functions. The use of a full-authority fly-by-wire system requires special care from a design and maintenance perspective, but it allows a greater range of enhanced control functions. One such function is the maneuver command pitch control law that optimizes handling qualities; suppresses any transients, or short-duration voltages (flight path upsets), caused by configuration changes or turbulence; and reduces weight by providing stability augmentation that allows the use of a smaller horizontal tail. The envelope protection functions enhance safety in all axes by helping the pilot avoid normal operational envelope exceedances.

   Return to article

Electrical signals are susceptible to voltage transients caused by lightning and high-intensity radiated fields (HIRF). The airplane critical flight control system, as well as all lightning/HIRF critical and essential systems, must be protected from these voltages for the life of the airplane. Boeing provides the initial protection in the airplane structure; shielding all cabling is additional protection. Operators are responsible for maintaining the protection by adhering to grounding practices for all components and inspecting the integrity of the shielding and shielding connections. Boeing develops scheduled maintenance requirements for continuous airworthiness using Air Transport Association maintenance steering group (MSG) revision 3 processes (MSG-3).

Establishing the requirements begins with extensive meetings of a working group that includes the original equipment manufacturer, operators, potential operators, the Joint Aviation Authorities, and the U.S. Federal Aviation Administration (FAA). The MSG outlines the initial minimum maintenance and inspection requirements for development of an approved continuous airworthiness maintenance program for the airframe, engines, systems, and components. Operators use these requirements as the basis for developing their own continuous airworthiness maintenance programs. The resulting maintenance tasks that operators must complete are then published in a maintenance review board report that Boeing submits to the FAA. Following approval, Boeing includes the tasks in the maintenance planning data document that is distributed to operators.

   Return to article

In addition to the scheduled maintenance that operators must accomplish on the 777, the FAA requested that Boeing develop and implement a lightning/HIRF protection assurance plan to help operators monitor the shield protection system over the life of the airplane. This plan tests certain critical and essential cables on six different in-service airplanes every four years to detect failed connectors, failed grounds, or other installation problems not found by operator-scheduled maintenance activity. The results of these periodic Boeing “validation” tests are compared with conditions that existed at the time of airplane delivery to determine if any degradation is occurring that might indicate an impending failure. In addition to flight control systems, the tests are developed to check engine control circuits, high lift systems, and some ARINC 629 circuits that are internal to the pressure hull.

| Boeing Home | Boeing Commercial |
Aero Copyright © The Boeing Company. All rights reserved.