1. A system for prescribing maintenance of helicopter engines belonging to the same engine class and formed by elements that vary over time depending on the technical condition thereof, the standard replacement of parts between engines, and the replacement of parts with different parts, comprising: a centralized database storing operational data relating to: working condition, describing the history of one or more working condition indicators of each of the engines, possible modifications and authorized modifications of the engines; a definition of maintenance plans for the engines according to predetermined values of the working condition indicator(s); a description of the probable causes of unscheduled events according to the data relating to possible and authorized modifications and the working condition data; maintenance applied, describing the history of maintenance operations applied to each of the engines; and instantiated configurations, describing the history of the configuration modifications applied to each of the engines; and means for acquiring the working condition indicator(s) of each of the engines and for updating the working condition data depending on the acquired value of the indicator(s) of each engine; means for identifying a maintenance operation to be applied to each of the engines depending on the operational data in the database; means for generating a continuous alarm for each identified maintenance operation to be performed; means for a digitally-signed updating of the applied maintenance data and the instantiated configuration data according to each maintenance operation applied to each of the engines; and means for deactivating an activated alarm if at least the digitally-signed update of the data resulting from the identified applied maintenance operation associated with the alarm is carried out.