The aviation industry's shift towards sustainable propulsion, notably hydrogen-electric propulsion (HEPS), underscores the need to grasp its effects on flight procedures and pilot duties. This research aims to develop a HEPS engine powertrain model for evaluating its influence on flight procedures, especially during critical phases like go-around for regional turboprop aircraft. The HEPS engine powertrain model was constructed by selecting powertrain components important for modelling based on their relevance to important HEPS system outputs like the thrust generation, battery discharge, and fuel left in the tank. Subsystems such as the fuel cell system, battery, motor, propeller etc. were modelled using MATLAB/Simulink and integrated to form a holistic representation of the HEPS engine. The model underwent testing through a simulated go-around mission, followed by an analysis of its operational envelope, which unveiled significant parameters influencing system behaviour during such manoeuvres. Among the critical parameters identified were the initial battery state of charge (SoC), nominal battery capacity, and propeller efficiency. Thrust generation limitations were identified for heavier aircraft configurations, as well as the relatively low impact of go-around speed on the system's power path. For a HEPS-based Dash 8 Q-300 aircraft with a mass of 38,000 pounds and a go-around speed of 96 knots, the State of Charge (SoC) of a 200Ah battery should be at least 23% for a successful go-around manoeuvre. Using appropriate parameters, the presented model framework assists in identifying such constraints and delineating flight procedural changes for future regional aircraft. The study highlights areas for model enhancement, including better thermal management system models for the fuel cell stack and battery, and improved motor-propeller models. This research contributes to sustainable aviation, guiding the integration of HEPS into flight operations for enhanced efficiency and eco-friendly air travel.