A Highly Monitored AV-8B Harrier II Digital Flight Control System 872332
The AV-8B Harrier II V/STOL strike aircraft for the U.S. Marine Corps features an advanced design, limited authority digital Stability Augmentation and Attitude Hold System (SAAHS). Utilization of this single channel electronic flight control system required an extensive self-test and monitoring system. New techniques to detect failures were based on extensive simulation, Iron Bird and flight test results.
Self-test capabilities are provided for maintainability as well as safety. SAAHS monitoring is implemented in three primary categories: hardware, software monitor of hardware, and software monitor of performance. Total system health is determined in a comprehensive preflight Built-in-Test (BIT). System performance during flight is continuously monitored by In-Flight-Monitoring (IFM).
The SAAHS self-test philosophy meets the requirements for detection of 98 percent of all possible failures and isolation of 99 percent of detected failures to a faulty weapons replaceable assembly (WRA) in the ground BIT mode. Furthermore, it meets the requirement for detection of 75 of all failures and isolation of 99 percent of these detected failures to a faulty WRA in the IFM mode.