1 - A method for automatic fault detection on the basis of data capable of representing a fault in an on-board system, which method includes: a step of determining at least two physical variables represented by the said data, the said physical variables including at least: one time-dependent variable representative of the persistence of an event in time and at least one instantaneous variable; a step of representing the said data by points of a space whose coordinates are the values of the said physical variables and a step of detecting a fault by employing a frontier defining a subspace of the said space in which the representation of a datum is associated with the detection of a fault.