1. A method of monitoring a computer system generating graphical images to be displayed in an aircraft cockpit, wherein the computer system generates an image of a graphical interface of a client application on the basis of a tree structure of graphical interaction objects composing said graphical interface, said method comprising: (a) obtaining graphical interaction objects arranged in a tree-structure organization; (b) selecting one of the graphical interaction objects and designating the selected graphical interaction object as a critical graphical interaction object, wherein the critical graphical interaction object has a dependency on another one of the graphical interaction objects in the tree-structure organization; (c) creating and adding to said tree structure, a new graphical interaction object which defines a critical graphical display zone; (d) modifying the dependency in the tree-structure organization of the critical graphical interaction object to depend from the new graphical interaction object and to remove the dependency on the another one of the graphical interaction objects; (e) repeating steps a to d at least once with respect to another critical graphical interaction object; (f) displaying the critical graphical interaction objects in the critical graphical display zone on a display screen connected to the computer system, and (g) performing critical monitoring of the critical graphical interaction objects and the new graphical interaction object, wherein the critical monitoring is not performed on the graphical interaction objects which are not one of the critical graphical interaction objects or one of the graphical interaction objects on which depends the critical graphical interaction objects.