The ARTERI concept for achieving engine control system fault detection, isolation, and accommodation is described. It uses analytical redundancy to improve system reliability in conjunction with or instead of hardware redundancy and can also be used as a diagnostic tool. The key elements of ARTERI include a real-time component level engine model for synthesizing sensor outputs, a component tracking filter for updating the model to match the actual engine, and a failure detection filter for detecting and isolating hard and soft system faults. Faults are accommodated by the use of model outputs in place of failed sensors and alternative operating schedules for minimizing performance degradation due to failed actuators. The design concept of each element is described and expected operating characteristics are discussed.