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In aviation, hot and high is a condition of low air density due to high ambient temperature and high airport elevation. Air density decreases with increasing temperature and altitude. At any given true airspeed, lower air density reduces the amount of lift generated by the wings or the rotors of an aircraft, which may hamper an aircraft's performance and hence its ability to operate safely. The reduced density also reduces the performance of the aircraft's engine, compounding the effect. Aviators gauge air density by calculating the density altitude. "Hot" and "high" do not have to be mutually inclusive of one another, though this tends to be the exception. If an airport is especially hot ''or'' high, the other condition need not be present. Temperatures can change from one hour to the next, while the elevation of an airport always remains constant. The fact that temperatures decrease at higher elevations mitigates the "hot and high" effect to a certain extent. ==Negative effects of hot and high conditions== * Airplanes require a longer takeoff run, potentially exceeding the amount of available runway. * Low air density hampers an aircraft's ability to climb. In some cases, an aircraft may be unable to climb rapidly enough to clear terrain surrounding a mountain airport. * Helicopters may be forced to operate in the shaded portion of the height-velocity diagram in order to become airborne at all. This creates the potential for an uncontrollable descent in the event of an engine failure. * Some aircraft, particularly light general aviation airplanes and older helicopters, have service ceilings so low that they may stall simply trying to maintain level flight. In some cases, aircraft have landed at high-altitude airports by taking advantage of cold temperatures only to become stranded as temperatures warmed and air density decreased. * Gliders (sailplanes) are especially vulnerable to hot and high conditions. Of course before being cut loose from a powered aircraft, they must be at a minimum altitude above the earth's surface. * While unsafe at any altitude, an overloaded aircraft is exponentially more dangerous under hot and high conditions. One notable crash was that of Jessica Dubroff's plane in 1996, flying out of the Cheyenne, Wyoming airport (elevation 6,159 ft / 1,878 m). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hot and high」の詳細全文を読む スポンサード リンク
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