Abstract: The structural integrity of a safe-life aircraft component on an aircraft is measured and assessed by a processing unit. The component includes a load-bearing metal element that is free from cracks. In the method, acoustic emissions generated in the metal element are converted into electronic signals. The acoustic emissions converted include relevant acoustic emissions resulting from changes in the structure of the element that make the element more susceptible to the formation of cracks. The electronic signals are set to a processing unit. The processing unit processes over time the signals in conjunction with stored reference data that allows a measure of the structural integrity to be made. Information providing a measure of the structural integrity of the aircraft component is outputted. Thus, deterioration of the structure of the component can be detected and monitored before a crack occurs.