1. A method for monitoring an aircraft, including a computer on board the monitored aircraft performing the steps of: collecting measurements made by sensors of variables related to current operation of the monitored aircraft, calculating a current state of the monitored aircraft from the collected measurements, sending a request to analyze the similarity of the calculated current state with previous states of aircrafts similar to the monitored aircraft, receiving and analyzing a change in operation of each similar aircraft having a previous state similar to the calculated current state to estimate a probable change in the future operation of the monitored aircraft, and if the estimated probable change is an abnormal change, sending an alert to a monitoring center on the ground to anticipate maintenance on the monitored aircraft.