The Safe Flight Envelope (SFE) is a prerequisite for flight envelope protection and essential for preventing Loss of Control (LoC) of a flying vehicle. Reachability analysis has been proposed for defining a SFE considering the dynamic characteristics of a system. However, the conventional Level Set approach for conducting reachability analysis is computational inefficient and impractical to solve problems having a state space with more than 4 dimensions. For this, we have proposed a computational efficient Monte-Carlo (MC) based approach. As an application, the SFE of an off-the-shelf quadrotor during the high-speed forward flight are estimated, based on the aerodynamic model identified from the high-speed flight data (V < 16 m/s). Taking into account the actuator dynamics, the state space of the problem has 6 dimensions in excess of the computational capabilities of the Level Set approach. By contrast, the result shows that the Monte-Carlo simulation based approach is able to solve this high dimension problem in a matter of seconds.