This paper represents Human Action study for Human Error analysis in a military modernization project where multi crew operation is required. Human errors need to be observed during simulated operational use of novelties and analyzed later (during the debriefing with pilots or during the results analysis). The main objective during the debriefing is to identify their causes, their consequence, their criticality and the current safety barriers in terms of human errors management.Simulation sessions offer wide range of capability to identify the problems in early stages of the design. Detailed Human Action pre-study is needed on those evaluations depending on the complexity of the military mission.Current paper does not specify the type of the aircraft or the details of the military missions. Proposed methodology can be used for different military multi-crew application. Possible Human Errors identified for different scenarios before the simulator sessions. This paper can be used in aircraft modernizations where complex avionics are used and the system must be tested against Human Action.