Method for performing maintenance on an engine, comprising the steps of: - providing an engine maintenance system, which comprises a database system having a database and a database management device; - providing at least one first performance parameter (Y pre) stored in the database, which characterizes the engine performance before an engine maintenance procedure; - providing at least one maintenance parameter stored in the database, which characterizes the scope of a maintenance measure performed on an engine within the context of an engine maintenance procedure; - providing at least one second performance parameter (Y post) stored in the database, which characterizes the engine performance after the engine maintenance procedure; characterized by the steps of: - detecting a functional relationship (ΔY modell) between different maintenance parameters (X i,j) and the contribution of the different maintenance parameters (X i,j) to a difference (ΔY mess,j) between the first performance parameter (Y pre) and the second performance parameter (Y post) by means of the database management device, the database comprising data (22', 24', 26') from past maintenance procedures on engines and comprising data (22", 24", 26") that is obtained on the basis of the engine currently to undergo maintenance, where: - the data (22', 22") contain "on-wing" and/or testing station data which are measured before maintenance is performed on the engine and are used for detecting the first performance parameter (Y pre); - the data (24', 24") characterize the scope of maintenance and are used for detecting the maintenance parameters (X i,j) for each maintenance measure, and - the data (26', 26") contain "on-wing" and/or testing station data which are measured after maintenance is performed on the engine and are used for detecting the second performance parameter (Y post); - detecting the impact of individual maintenance measures on the total effect expected on the engine performance on the basis of the data (22', 24', 26') from previous maintenance procedures and the data (22", 24") currently detected at the engine by means of the database management device; - outputting the functional relationship by means of the engine maintenance system; and - performing maintenance on the engine, taking into account the functional relationship. - providing an engine maintenance system, which comprises a database system having a database and a database management device; - providing at least one first performance parameter (Y pre) stored in the database, which characterizes the engine performance before an engine maintenance procedure; - providing at least one maintenance parameter stored in the database, which characterizes the scope of a maintenance measure performed on an engine within the context of an engine maintenance procedure; - providing at least one second performance parameter (Y post) stored in the database, which characterizes the engine performance after the engine maintenance procedure; characterized by the steps of: - detecting a functional relationship (ΔY modell) between different maintenance parameters (X i,j) and the contribution of the different maintenance parameters (X i,j) to a difference (ΔY mess,j) between the first performance parameter (Y pre) and the second performance parameter (Y post) by means of the database management device, the database comprising data (22', 24', 26') from past maintenance procedures on engines and comprising data (22", 24", 26") that is obtained on the basis of the engine currently to undergo maintenance, where: - the data (22', 22") contain "on-wing" and/or testing station data which are measured before maintenance is performed on the engine and are used for detecting the first performance parameter (Y pre); - the data (24', 24") characterize the scope of maintenance and are used for detecting the maintenance parameters (X i,j) for each maintenance measure, and - the data (26', 26") contain "on-wing" and/or testing station data which are measured after maintenance is performed on the engine and are used for detecting the second performance parameter (Y post); - the data (22', 22") contain "on-wing" and/or testing station data which are measured before maintenance is performed on the engine and are used for detecting the first performance parameter (Y pre); - the data (24', 24") characterize the scope of maintenance and are used for detecting the maintenance parameters (X i,j) for each maintenance measure, and - the data (26', 26") contain "on-wing" and/or testing station data which are measured after maintenance is performed on the engine and are used for detecting the second performance parameter (Y post); - detecting the impact of individual maintenance measures on the total effect expected on the engine performance on the basis of the data (22', 24', 26') from previous maintenance procedures and the data (22", 24") currently detected at the engine by means of the database management device; - outputting the functional relationship by means of the engine maintenance system; and - performing maintenance on the engine, taking into account the functional relationship.