Boeing 777 High Lift Control System

The Boeing 777 High Lift Control System (HLCS) is a state-of-the-art microprocessor-based system that provides fly-by-wire control, protection and built-in-test and maintenance access functions for the leading edge flaps and trailing edge flaps drive and actuation systems. This system is designed to take advantage of technologically proven concepts as well as judicious application of new concepts in response to market demands, airline customer input and a thorough review of lessons learned from previous aircraft programs. The HLCS is comprised of two independent control lanes; a control lane is defined as an FSEU (Flap/Slat Electronics Unit), associated flap lever sensors, associated flap and slat position sensors, and flap and slat solenoid coils. Control is alternated between the two control lanes with each flight to limit exposure time to latent faults. Each FSEU has a control channel and a monitor channel that use dissimilar microprocessors. Each channel monitors the other and transfers control to the other FSEU lane if there is a disagreement between them, or if other failures are detected. The system may be operated in three modes, primary (hydraulic drive power), secondary (electric drive power) and alternate (electric drive power). Primary and secondary modes are fly-by-wire control via the FSEUs and flap lever. Alternate mode is a hardwired electrical control mode