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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. The lower air density reduces the power output from an aircraft's engine and also requires a higher true airspeed before the aircraft can become airborne. Aviators gauge air density by calculating the density altitude. [1]
An airport may be especially hot or high, without the other condition being present. Temperature and pressure altitude can change from one hour to the next. The fact that temperature generally decreases as altitude increases mitigates the "hot and high" effect to a small 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 did, however, produce a version of its popular Boeing 727 with JATO 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 and only intended to operate as an emergency fallback in the case of an engine failure during takeoff. [2]
Several manufacturers of early jet airliners offered variants optimized for hot and high operations. Such aircraft generally offered the largest wings and/or the most powerful engines in the model lineup coupled with a small fuselage to reduce weight. Some such aircraft include:
The marketing failure of most of these airplanes demonstrated that airlines were generally unwilling to accept reduced efficiency at cruise and smaller ultimate load-carrying capacity in return for a slight performance gain at particular airports. Rather than accepting these drawbacks, it was easier for airlines to demand the construction of longer runways, operate with smaller loads as conditions dictated, or simply drop the unprofitable destinations.
Furthermore, as the second generation of jet airliners began to appear in the 1970s, some aircraft were designed to eliminate the need for a special "hot and high" variant – for instance, the Airbus A300 can perform a 15/0 takeoff, where the leading edge slats are adjusted to 15 degrees and the flaps kept retracted. This takeoff technique is only used at hot and high airports, for it enables a higher climb limit weight and improves second segment climb performance.
Most jetliner manufacturers have dropped the "hot and high" variants from their model lineups.
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Notable examples of hot and high airports include:[ citation needed ]
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The maximum takeoff weight (MTOW) or maximum gross takeoff weight (MGTOW) or maximum takeoff mass (MTOM) of an aircraft, also known as the maximum structural takeoff weight or maximum structural takeoff mass, is the maximum weight at which the pilot is allowed to attempt to take off, due to structural or other limits. The analogous term for rockets is gross lift-off mass, or GLOW. MTOW is usually specified in units of kilograms or pounds.
The density altitude is the altitude relative to standard atmospheric conditions at which the air density would be equal to the indicated air density at the place of observation. In other words, the density altitude is the air density given as a height above mean sea level. The density altitude can also be considered to be the pressure altitude adjusted for a non-standard temperature.
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