Fatal accidents in complex system, as military and civil aviation, generally occur through the accumulation of multiple factors (including pilot fatigue or overload). Even though these accidents are rare – one accident per one million of aircraft take-offs -, it is universally agreed that 80 percent of aviation incidents (defined as an occurrence, other than an accident, associated with specific procedures that affect the operation safety) involves human factors. The human dimension is the determinant factor in producing and, in turn, avoiding potential hazards. Military aviators are required to perform long and continuous daytime/nighttime operations to gain a tactical advantage over the enemy, and have to face very complex situations (including emergencies) at any time. Thus, the development of non-invasive methods to monitor and detect fatigue and/or cognitive overload in soldiers, and, thus, prevent catastrophic outcomes in operational environments, is an area of great interest to our society.