1. A method for a computer-aided preparation of a diagnostic report for a system of an aircraft comprising a plurality of subsystems, at least one subsystem of said plurality of subsystems comprising a subsystem having a computer processor and performing monitoring and notification of at least one detected event, the method comprising: implementing, via the computer processor, a critical event chart substantially modelling said system, said critical event chart comprising a plurality of nodes, each node of said plurality of nodes being linked by a logical implication relation to at least one other node of said plurality of nodes, said plurality of nodes comprising: a plurality of nodes each representing a notification message capable of being received; at least one node representing a critical event; and, a plurality of nodes each representing an element of said system, which is liable to failure, and each such element comprising a suspect candidate item; receiving, via the computer processor, at least one notification message of the occurrence of said at least one detected event, said detected event comprising said at least one node representing said critical event; creating, via the computer processor, a minimal diagnostic set relative to said at least one detected event, comprising a plurality of said elements each represented by a node of said critical event chart, each element of said minimal diagnostic set being determined according to at least one logical implication relation of said critical event chart with said node representing said critical event associated with said at least one received notification message; and ranking, via the computer processor, at least one of said elements of said minimal diagnostic set, said ranked elements forming part of said diagnostic report; calculating, via the computer processor, a historic persistence weighting for each suspect candidate item in a current flight; performing, via the computer processor, prioritization of at least one of minimal hitting sets of suspect candidate items based on said historic persistence weighting for establishing a diagnosis relating to the current flight, each hitting set comprising some nodes, and at least one of said hitting sets being minimal when no other hitting set is included in it, said prioritization being determined based on a cardinality of said at least one of said minimal hitting sets and a relevance score being calculated by a sum of corresponding historic persistence weightings of said each suspect candidate item in said minimal hitting set; and displaying diagnostic results of said diagnostic report via a human-machine interface.