Apparatus for checking the operational characteristics of a complex installation used in the flight control of an aircraft before starting of the installation with said installation comprising at least one system of combined electronic devices having a fixed and predetermined configuration defining essential functional specifications of such devices in said system, and having functional units connected to outputs of the combined devices for receiving control signals, and with said apparatus comprising computer means having a memory with a reference base in which each device is recorded an identification code corresponding to the structure and the functional specifications of the device, the identification codes of the devices being recorded in said reference base of said memory with the reference base containing a dictionary of the devices which are interchangeable and compatible with the devices of the installation, said memory further containing a program for checking before starting the installation if a device of the installation is interchangeable with a new device by reference to said dictionary in said reference base and a program for comparing identification codes of the devices in said reference base before changing the configuration of the installation with the identification codes of the devices of the installation after changing at least one device in said system, this changing giving to the installation a new configuration, the apparatus further comprising display means connected to said computer means so as to supply an alarm message on account of an unauthorized configuration modification if the configuration change is not compatible with the reference base, to indicate the causes of this unauthorized modification and to indicate the identification code of the device changed in the installation causing this alarm with said display means also providing a message relating to the authorization of use of the new configuration when the comparison has not triggered the alarm and with such new configuration then being recorded in said memory.