Background: Continuous medical education is essential in Helicopter Emergency Medical Services (HEMS). In-situ simulation training makes it possible to train in a familiar environment. The use of a dedicated facilitator is essential; however, when an in-situ simulation training session is interrupted by a live mission, the efforts invested in the training are left unfulfilled. This study aims to evaluate if HEMS mission observation and debriefing by the simulation facilitator is a feasible alternative to mission-interrupted simulation training, and how this alternative to simulation training is perceived by both facilitators and HEMS crew members. Methods: Facilitator observation during live missions and post-mission debriefing was offered as an alternative to mission-interrupted simulation training over a one-year period at three HEMS bases. Immediate feedback was requested from crews and facilitators after each observed live mission on a predefined questionnaire. At the end of the study period, semi-structured interviews were performed with a sample of HEMS crew members and facilitators to further explore the experience with the concept. Numerical data about the sessions were recorded continuously. Results: A total of 78 training sessions were attempted, with 46 (59%) of the simulations conducted as planned. Of the remaining, 23 (29%) were not started because the crew had other duties (fatigued crew or crew called for a mission where observation was inappropriate/impossible), and 9 (12%) training sessions were converted to observed live missions. In total, 43 (55%), 16 (21%) and 19 (24%) attempts to facilitate simulation training were undertaken on the three bases, respectively. The facilitators considered mission observation more challenging than simulation. The interviews identified local know-how, clinical skills, and excellent communication skills as important prerequisites for the facilitators to conduct live mission observation successfully. Participating crews and facilitators found simulation both valuable and needed. Being observed was initially perceived as unpleasant but later regarded as a helpful way of learning. Conclusion: Live mission observation and debriefing seems a feasible and well-received alternative to an in-situ simulation program in HEMS to maximise invested resources and maintain the learning outcome. Furthermore, additional training of simulation facilitators to handle the context of live mission observation may further improve the learning output.