Literature on transfer of training largely deals with positive transfer. Only few studies exist on negative transfer, and these were often performed in (laboratory) environments with low ecological validity. This study's objective is to identify factors that contribute to negative transfer in safety-critical professions. The primary focus of the study is on aviation, but investigated principles also apply to other domains with high-performing professionals. Semi-structured interviews were performed with training experts from commercial and military aviation (n = 8), as well as the medical (n = 1) and maritime (n = 1) domain. The experts were asked to list examples of negative transfer that they have observed or experienced themselves. Follow-up questions addressed training approaches and solutions regarding these examples. Answers were categorized using a transfer framework. The experts' most salient concerns involved: Time pressure, which leads to rushed training; Instructors with insufficient understanding of the limitations of the (simulator) training; and the way in which trainees should be placed into hazardous situations in a realistic manner. The experts provided several factors and recalls of experiences which may lead to negative transfer. These results may be relevant for instructors and can provide input for further experimental research regarding negative transfer.