Evaluating the operating safety of a complex software and or hardware system such as a system for displaying flight information on an instrument panel of an aircraft. The evaluation method includes construction of a first architecture of the system, divided into several blocks each comprising data inputs/outputs, the inputs of a block being connected to the outputs of other blocks in the first architecture; identification of failures of the outputs of the blocks of the architecture; construction of first boolean expressions expressing the states of the outputs of the blocks of the first architecture as a function of the states of the identified failures, of the states of the inputs of the blocks; definition of a first feared event to be examined by a second boolean expression constructed based on the first boolean expressions; and reduction of the second boolean expression in a sum of monomials.