<p>Additive manufacturing transforms the aerospace industry by enabling lightweight structures, greater design freedom, cost reduction, and improved supply chain efficiency. However, the widespread adoption of additive manufacturing is hindered due to strict certification requirements and material property variations caused by anisotropy and printing process-dependent factors. While significant research has focused on optimizing printing parameters, an equally critical challenge lies in the influence of mechanical testing protocols on material characterization. Discrepancies between widely used ISO and ASTM testing methodologies can lead to variations in reported mechanical properties, ultimately impacting design allowables, simulation accuracy, and certification pathways. The mechanical behaviour of aerospace-grade thermoplastic ULTEM 9085 was studied by means of tension, flexural, and compression tests across all print orientations. A comparative analysis of ISO and ASTM standards was conducted at strain rates of 2.5, 5, and 10 mm/min to evaluate their influence on measured properties. The results highlight variations between the above-mentioned standards, affecting mechanical properties in all orientations. These findings emphasize the importance of standard selection and strain rate considerations in additive manufacturing material qualification, particularly for aerospace applications. By providing comparative data, this study supports standardization efforts and enhances the accuracy of simulation models for structural performance prediction, ultimately facilitating the broader adoption of additively manufactured components in aerospace.</p>