1. A method for the computer-aided preparation of a diagnostic report for a complex system of an aircraft comprising a plurality of subsystems, at least one subsystem of said plurality of subsystems comprising a subsystem configured for monitoring and notification of at least one detected event, the method comprising: implementing a critical event chart at least partially modelling said complex 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 complex system, each element represented by a node being liable to failure; receiving at least one notification message of the occurrence of said at least one detected event; creating a minimal diagnostic set relative to said at least one detected event, comprising a plurality of 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 a node representing said at least one received notification message; and ranking at least some of said elements of said minimal diagnostic set, said ranked elements forming part of said diagnostic report.