Electromagnetic measurements in aircraft are performed for different purposes, e.g. assessing the interference potential of electronic devices, the antenna-to-antenna coupling or the behaviour of wireless links. In order to accomplish reliable and relevant evaluations, it is crucial that the quality of the measurement results should be considered. This is especially important in view of the system size and the complex electromagnetic conditions which prevail in aircraft. Taking as basis interference path loss measurements carried out in aircraft, procedures for evaluating their reliability are presented. In particular, it is found that parasitic coupling in the measurement setup and external conditions can significantly affect the results. The influence of the manual placement of the transmitting antenna, antenna inclination, and hangar is also discussed in this paper. It is essential to have a high-quality measurement setup and to perform check measurements and analyses that can validate the measurement procedures.