During the operation of aero-engines (turbine and piston engines), wear processes occur in tribological nodes, which significantly affect the reliability and safety of flight operations. This paper presents aspects of tribological diagnostics of aircraft engines based on periodic testing of lubricant samples in laboratories. Firstly, the object of research with its design features, operating parameters and used lubricants is presented, as well as the theoretical basis of tribological testing. This was followed by a description of the testing methods used in tribological diagnostics of aero-engines, taking into account lubricant degradation and contamination processes, standards, testing methodologies and operating experience described in the literature, including the machine failure curve. Next, the capabilities of the testing methods are illustrated with results from periodic tribological testing of turbine engines, obtained at an accredited tribological systems diagnostics laboratory. In the following section, the role of trend analysis and statistical criteria in the process of diagnosing and managing the risk of operation of aero-engines, exploited according to both their technical condition and planned maintenance, was indicated. Then, the possibility of improving the reliability of tribological diagnostics of aero-engines on the basis of experience from industry - real-time monitoring of selected tribological parameters - was signalled. In conclusion, the high efficiency and role of tribological diagnostics in maintaining the operational safety of a fleet of different aircraft types is indicated.