When it comes to good old-fashioned hangar flying sessions, one subject that almost never seems to be discussed is density altitude. The reason being, too many pilots do not know enough about the subject. Yet, because of the inescapable influence density altitude has on aircraft and engine performance, it is important that every pilot understand its effects. Hot, high, and humid weather conditions can change a routine takeoff or landing into an accident in less time than it takes to tell about it. There are three important factors that affect air density; ALTITUDE, TEMPERATURE, and HUMIDITY.