Automatic diagnostic method for monitoring a state of health of at least one engine equipping an aircraft , said method including the following steps: • periodic in-flight acquisition of a plurality of flight data using sensors , said plurality of flight data being representative of a plurality of physiochemical parameters, • identifying using a controller , based on said plurality of flight data, at least one predetermined engine health control phase and isolating using said controller a sequence of meaningful data from among said plurality of flight data produced during said at least one engine health control phase, said meaningful data of a sequence being acquired successively, and • for each engine health control phase, calculating using said controller at least one engine health index as a function of at least one control parameter of said at least one engine from among said plurality of physiochemical parameters, characterized in that said method includes the following steps: • for each engine health index, generating using said controller a point of a map with at least one dimension, each point associating said engine health index with at least one value of at least one predetermined state parameter from among said plurality of physiochemical parameters, each predetermined state parameter corresponding to a dimension of said map, each value corresponding respectively to a value of said at least one state parameter at a moment of said sequence of meaningful data for which said engine health index is calculated, • grouping using said controller said points of said map into at least one class of interest (Ci1, Ci2), each class of interest (Ci1, Ci2) corresponding to a group of points spaced apart from one another in said map by a predetermined maximum distance, • monitoring using said controller said engine health indices corresponding to said points of said at least one class of interest (Ci1, Ci2), and • generating using an alerting device an information signal as a function of said engine health indices monitored during said monitoring . • periodic in-flight acquisition of a plurality of flight data using sensors , said plurality of flight data being representative of a plurality of physiochemical parameters, • identifying using a controller , based on said plurality of flight data, at least one predetermined engine health control phase and isolating using said controller a sequence of meaningful data from among said plurality of flight data produced during said at least one engine health control phase, said meaningful data of a sequence being acquired successively, and • for each engine health control phase, calculating using said controller at least one engine health index as a function of at least one control parameter of said at least one engine from among said plurality of physiochemical parameters, • for each engine health index, generating using said controller a point of a map with at least one dimension, each point associating said engine health index with at least one value of at least one predetermined state parameter from among said plurality of physiochemical parameters, each predetermined state parameter corresponding to a dimension of said map, each value corresponding respectively to a value of said at least one state parameter at a moment of said sequence of meaningful data for which said engine health index is calculated, • grouping using said controller said points of said map into at least one class of interest (Ci1, Ci2), each class of interest (Ci1, Ci2) corresponding to a group of points spaced apart from one another in said map by a predetermined maximum distance, • monitoring using said controller said engine health indices corresponding to said points of said at least one class of interest (Ci1, Ci2), and • generating using an alerting device an information signal as a function of said engine health indices monitored during said monitoring . <EOS>