Abstract: An exemplary embodiment of the invention is an engine diagnostic system including a plurality of sensors. One of the plurality of sensors includes a speed sensor generating a speed value indicative of aircraft speed. A processor is coupled to the sensors and stores prior mission data and current mission data in a data memory when the speed value is within a predetermined velocity range. A fault indicator is provided which is visible from the exterior of the aircraft. The processor detects a presence or absence of a fault in response to the prior mission data and current mission data and activates the fault indicator in response to the presence of a fault. Another exemplary embodiment of the invention is a method for detecting faults in an aircraft. The method includes determining when aircraft speed is within a predetermined velocity range and obtaining current mission data in response to the aircraft speed being within the velocity range.