The prominence of aviation security has increased dramatically in recent years. As a reaction to the new threat situation large investments into modern security technology have been made. State-of-the-art X-ray screening equipment provides high resolution images, many image enhancement features and even automatic explosive detection. However, the most expensive equipment is of limited value if the humans who operate it are not selected and trained to perform their task accurately and efficiently. In fact, according to several experts, the human operator is currently the weakest link in aviation security. This article presents results of studies conducted over the last four years which clearly show that threat detection in X-ray images can be increased substantially by investing into human factors technologies that are based on results of visual cognition, object recognition and psychophysics.