PURPOSE: To facilitate the management maintenance of an aircraft by recording a period when the display value of an indicator exceeds a threshold at the time of operation and the degree and permitting the specified indicator on a normal operation state and a use situation to output cover data on the engine operation state and the like.

CONSTITUTION: A computer system is provided with the prescribed threshold on the display value of the specified indicator and it is arranged so that it records time when the display value exceeds the threshold when the aircraft is operated and the degree. The indicator can be provided with a means for measuring stress generated in one of the engine of the aircraft, a transmission or a body or more than one constitution parts. A means for calculating low frequency fatigue from stress information obtained on the constitution parts and recording information which is calculated for preparation for the processing of a next stage can be provided on the computer system. Thus, the management maintenance of the aircraft becomes easy.