A method comprising: performing at least one baseline structural interrogation of a physical structure (12A-12N) in one or more corresponding baseline conditions of the structure (12A-12N); storing, by a controller , the one or more baseline conditions of the structure (12A-12N) corresponding to the at least one baseline structural interrogation; sensing, using at least one sensor (16A-16N), one or more current conditions of the structure; determining, by the controller , whether a difference between the one or more current conditions and the one or more baseline conditions satisfies at least one threshold deviation criterion, wherein the at least one threshold deviation criterion includes a maximum deviation between the one or more baseline conditions of the structure (12A-12N) and the one or more current conditions of the structure (12A-12N); characterized in that when it is determined that the difference between the one or more current conditions and the one or more baseline conditions satisfies the at least one threshold criterion, in response: performing a current structural interrogation of the structure (12A-12N); but when it is determined that the difference between the one or more current conditions and the one or more baseline conditions does not satisfy the at least one threshold criterion, in response: outputting, by the controller , an indication that the at least one threshold deviation criterion is not satisfied; wherein the controller is operable to receive a user input acknowledging that the one or more threshold deviation criterion are not satisfied and requesting that a current structural interrogation be performed regardless and, when the controller receives said user input, the method comprises the controller , in response to said user input: performing a current structural interrogation of the structure (12A-12N); and storing the results of the current structural interrogation in association with the one or more current conditions of the structure. performing at least one baseline structural interrogation of a physical structure (12A-12N) in one or more corresponding baseline conditions of the structure (12A-12N); storing, by a controller , the one or more baseline conditions of the structure (12A-12N) corresponding to the at least one baseline structural interrogation; sensing, using at least one sensor (16A-16N), one or more current conditions of the structure; determining, by the controller , whether a difference between the one or more current conditions and the one or more baseline conditions satisfies at least one threshold deviation criterion, wherein the at least one threshold deviation criterion includes a maximum deviation between the one or more baseline conditions of the structure (12A-12N) and the one or more current conditions of the structure (12A-12N); characterized in that when it is determined that the difference between the one or more current conditions and the one or more baseline conditions satisfies the at least one threshold criterion, in response: performing a current structural interrogation of the structure (12A-12N); but when it is determined that the difference between the one or more current conditions and the one or more baseline conditions does not satisfy the at least one threshold criterion, in response: outputting, by the controller , an indication that the at least one threshold deviation criterion is not satisfied; wherein the controller is operable to receive a user input acknowledging that the one or more threshold deviation criterion are not satisfied and requesting that a current structural interrogation be performed regardless and, when the controller receives said user input, the method comprises the controller , in response to said user input: performing a current structural interrogation of the structure (12A-12N); and storing the results of the current structural interrogation in association with the one or more current conditions of the structure. <EOS>