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 Environmental The Airfield Layout Logans airfield layout, illustrated in Figure 1, consists of five runways, which vary in length from 2,557 feet to 10,081 feet. Logans runways are aligned in three directions with runway ends pointing toward six distinct compass headings. Aircraft must generally take off and land into the wind, so the availability of specific runway configurations is determined by wind speed and direction, and other weather conditions. The runway layout provides necessary operating flexibility given Logans coastal location and highly variable wind conditions. Non-coastal airports that do not experience the same variation in wind conditions may have a simpler airfield layout and fewer required operating configurations. 
Runway Use Configurations
There are several primary runway configurations in use at Logan, with over 80 operating subsets of these configurations. The operational capacities of Logans existing configurations range from a maximum of approximately 120 operations per hour when the weather is good, winds are light, and three runways are available, to fewer than 60 hourly operations for a single runway. 
Logans highest capacity configurations have three active runways which allow FAA controllers to segregate arriving aircraft of different size classes into two arrival streams and to use the third runway for aircraft departures. High capacity runway configurations are available at Logan nearly 80 percent of the year. For the remaining part of the year, poor wind and weather conditions restrict the airport to low capacity configurations with just one or two available runways.
As shown in Figures 2 to 3, (figures are ordered top to bottom, please mouse over images for more information) the north-south configurations are the highest capacity configurations at Logan. These configurations include the Runways 4L, 4R, and 9 configuration and the Runways 22L, 22R, and 27 configuration. With three available runways, these configurations maximize the airports operating efficiency by providing two runways for arriving aircraft, which permits air traffic control to segregate aircraft of different size classes. Conversely, when the airport is restricted to a two-runway or one-runway configuration with a single arrival stream, airfield capacity drops significantly. As shown in Figures 4 to 6, Logan is restricted to two or one runway(s) when operating in an east/west orientation. These low capacity configurations include the east/southeast configuration of Runways 15R and 9, and the west/northwest configuration using Runways 27 and 33L. Under high northwest winds, Logan can be restricted to just a single runway, Runway 33L, to handle all arriving and departing aircraft.
Because Logan lacks a third available runway in the east-west direction and Runway 15L/33R is too short to be used by most aircraft, the north-south runway configurations are utilized most frequently (see Figure 7). In 1998, 76 percent of Logans jet operations landed on or departed from the north/south runway configurations (Runways 4L and 4R arrivals, 4R departures, Runway 9 departures, 22L and 22R departures, and 22L and 27 arrivals). As a result, communities affected by the north/south runway configurations bear a disproportionate share of jet overflights. Conversely, 11 percent of Logans 1998 jet operations were on runways affecting communities west of the airport (Runway 27 and 33L departures, and 15R arrivals) and 13 percent utilized over-the-water runways (15R for departures and 33L for arrivals).
Figure 7 illustrates the percentage of time that winds from different directions occur at Logan during a typical year. In light winds and good visibility, high capacity three-runway configurations are generally available. With moderate northeast and southwest winds, Logan can also operate on high capacity runway configurations. With northeast winds, the Runways 4L, 4R and 9 configuration is available for use (see Figure 2). When wind direction shifts to the southwest, the Runways 22L, 22R and 27 configuration is used (see Figure 3).
Under moderate northwest winds, Logan is forced to use the low-capacity Runway 27 and 33L configuration (see Figure 5).
When northwest winds are especially strong or gusty, Runway 27 cannot be used due to excessive crosswinds. Under these conditions, Runway 33L is the only runway available for both landings and takeoffs (see Figure 6). 
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