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A holding pattern is a circular or oval flight route used by aircraft to remain airborne without leaving an area, often due to excessive traffic or poor ground conditions. Multiple holding patterns can be established for a single airport, and each will have its own area and route course. It is generally preferable to avoid holding patterns due to their wastefulness with respect to time and fuel.
A holding pattern is a route that an aircraft can fly, typically in an oval formation, that allows the aircraft to remain airborne without leaving an area. This type of flight pattern is generally used when an aircraft has reached a destination but is unable to land, often due to excessive aircraft traffic or poor ground conditions. Multiple holding patterns in different airspaces can be established for a single airport if it is busy enough, and each will have its own area and route course. A holding pattern can also be used to maintain multiple aircraft in a single route pattern, each separated by vertical distance.
Typically used at major airports, a holding pattern can be any route that ultimately results in a complete loop returning an aircraft to a stationary starting point. The simplest type of route, and the easiest to visualize, is a circle or oval, much like a racetrack used by a car. An aircraft will enter this route at a stationary point, called a fix, and then move through the pattern until it returns to the fix. For an oval clamping pattern, this generally means that each turn takes about a minute to complete, and each side is long enough to require another minute or more to complete.
Holding patterns with longer sides are generally used for longer holds, as frequent turning can make airplane passengers uncomfortable. A holding pattern is typically used at a busy airport to keep incoming aircraft airborne around the airport while waiting for the landing area to be ready or accessible. This may be necessary if traffic is heavy or ground conditions are poor and snow or ice must be removed before the aircraft can land safely. Multiple aircraft may use a single holding pattern; each one is placed in the pattern higher than the last, creating a vertical stack of planes.
When using this type of holding pattern stack, each approaching aircraft is instructed to enter the stack at a higher position, with the lower aircraft landing first. Once the bottom ship leaves the holding stack, each aircraft is moved down and the process continues as needed. Since a holding pattern is quite wasteful with respect to time and fuel, it is generally preferable to avoid it; Most airlines try to plan ahead for landing problems, delaying takeoff rather than keeping planes airborne. Holding patterns can also be used in certain emergency situations, such as an aircraft having to land without landing gear, to burn off excess fuel and reduce the possibility of a fuel fire or explosion.
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