Hot and high

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.

Some ways to increase aircraft performance in hot and high conditions include:

Auxiliary rockets and/or jet engines can help a fully loaded aircraft to take off within the length of the runway. The rockets are usually one-time units that are jettisoned after takeoff. This practice was common in the 1950s and 60s, when the lower levels of thrust from military turbojets was inadequate for takeoff from shorter runways or with very heavy payloads. It is now seldom used.

Auxiliary jets and rockets have rarely been used on civil aircraft due to the risk of aircraft damage and loss of control if something were to go wrong during their use. Boeing produced a JATO-powered version of its popular Boeing 727 primarily for "hot and high" operations out of Mexico City Airport (MMMX) and La Paz, Bolivia. The boosters were located adjacent to the main landing gear at the wing root on each side of the aircraft.

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Wikipedia