AIM 8/15/19  Section 3. Airport Operations 4 − 3 − 1. General 4 − 3 − 2. Airports with an Operating Control Tower NOTE − Increased traffic congestion, aircraft in climb and descent attitudes, and pilot preoccupation with cockpit duties are some factors that increase the hazardous accident potential near the airport. The situation is further compounded when the weather is marginal, that is, just meeting VFR requirements. Pilots must be particularly alert when operating in the vicinity of an airport. This section defines some rules, practices, and procedures that pilots should be familiar with and adhere to for safe airport operations. a. When operating at an airport where traffic control is being exercised by a control tower, pilots are required to maintain two − way radio contact with the tower while operating within the Class B, Class C, and Class D surface area unless the tower authorizes otherwise. Initial callup should be made about 15 miles from the airport. Unless there is a good reason to leave the tower frequency before exiting the Class B, Class C, and Class D surface areas, it is a good operating practice to remain on the tower frequency for the purpose of receiving traffic information. In the interest of reducing tower frequency congestion, pilots are reminded that it is not necessary to request permission to leave the tower frequency once outside of Class B, Class C, and Class D surface areas. Not all airports with an operating control tower will have Class D airspace. These airports do not have weather reporting which is a requirement for surface based controlled airspace, previously known as a control zone. The controlled airspace over these airports will normally begin at 700 feet or 1,200 feet above ground level and can be determined from the visual aeronautical charts. Pilots are expected to use good operating practices and communicate with the control tower as described in this section. b. When necessary, the tower controller will issue clearances or other information for aircraft to generally follow the desired flight path (traffic patterns) when flying in Class B, Class C, and Class D surface areas and the proper taxi routes when operating on the ground. If not otherwise authorized This diagram is intended only to illustrate terminology used in identifying various components of a traffic pattern. It should not be used as a reference or guide on how to enter a traffic pattern. c. The following terminology for the various components of a traffic pattern has been adopted as standard for use by control towers and pilots (See FIG 4 − 3 − 1): 1. Upwind leg. A flight path parallel to the landing runway in the direction of landing. 2. Crosswind leg. A flight path at right angles to the landing runway off its takeoff end. 3. Downwind leg. A flight path parallel to the landing runway in the opposite direction of landing. 4. Base leg. A flight path at right angles to the landing runway off its approach end and extending from the downwind leg to the intersection of the extended runway centerline. 5. Final approach. A flight path in the direction of landing along the extended runway centerline from the base leg to the runway. 6. Departure. The flight path which begins after takeoff and continues straight ahead along the extended runway centerline. The departure climb continues until reaching a point at least $^{1}$/$_{2}$ mile 4 − 3 − 1 Airport Operations or directed by the tower, pilots of fixed − wing aircraft approaching to land must circle the airport to the left. Pilots approaching to land in a helicopter must avoid the flow of fixed − wing traffic. However, in all instances, an appropriate clearance must be received from the tower before landing. FIG 4 − 3 − 1 Components of a Traffic Pattern