AIM 4-3-2

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4-3-2. Airports with an Operating Control Tower

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 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

NOTE-
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 leg. 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 beyond the departure end of the runway and within 300 feet of the traffic pattern altitude.

d. Many towers are equipped with a tower radar display. The radar uses are intended to enhance the effectiveness and efficiency of the local control, or tower, position. They are not intended to provide radar services or benefits to pilots except as they may accrue through a more efficient tower operation. The four basic uses are:

1. To determine an aircraft's exact location. This is accomplished by radar identifying the VFR aircraft through any of the techniques available to a radar position, such as having the aircraft squawk ident. Once identified, the aircraft's position and spatial relationship to other aircraft can be quickly determined, and standard instructions regarding VFR operation in Class B, Class C, and Class D surface areas will be issued. Once initial radar identification of a VFR aircraft has been established and the appropriate instructions have been issued, radar monitoring may be discontinued; the reason being that the local controller's primary means of surveillance in VFR conditions is visually scanning the airport and local area.
2. To provide radar traffic advisories. Radar traffic advisories may be provided to the extent that the local controller is able to monitor the radar display. Local control has primary control responsibilities to the aircraft operating on the runways, which will normally supersede radar monitoring duties.
3. To provide a direction or suggested heading. The local controller may provide pilots flying VFR with generalized instructions which will facilitate operations; e.g., "PROCEED SOUTHWESTBOUND, ENTER A RIGHT DOWNWIND RUNWAY THREE ZERO," or provide a suggested heading to establish radar identification or as an advisory aid to navigation; e.g., "SUGGESTED HEADING TWO TWO ZERO, FOR RADAR IDENTIFICATION." In both cases, the instructions are advisory aids to the pilot flying VFR and are not radar vectors.

NOTE-
Pilots have complete discretion regarding acceptance of the suggested headings or directions and have sole responsibility for seeing and avoiding other aircraft.

4. To provide information and instructions to aircraft operating within Class B, Class C, and Class D surface areas. In an example of this situation, the local controller would use the radar to advise a pilot on an extended downwind when to turn base leg.

NOTE-
The above tower radar applications are intended to augment the standard functions of the local control position. There is no controller requirement to maintain constant radar identification. In fact, such a requirement could compromise the local controller's ability to visually scan the airport and local area to meet FAA responsibilities to the aircraft operating on the runways and within the Class B, Class C, and Class D surface areas. Normally, pilots will not be advised of being in radar contact since that continued status cannot be guaranteed and since the purpose of the radar identification is not to establish a link for the provision of radar services.

e. A few of the radar equipped towers are authorized to use the radar to ensure separation between aircraft in specific situations, while still others may function as limited radar approach controls. The various radar uses are strictly a function of FAA operational need. The facilities may be indistinguishable to pilots since they are all referred to as tower and no publication lists the degree of radar use. Therefore, when in communication with a tower controller who may have radar available, do not assume that constant radar monitoring and complete ATC radar services are being provided.

Aeronautical Information Manual (AIM) — Chapter 4 — Air Traffic Control
4-1-1 ARTCCs • 4-1-2 Towers • 4-1-3 FSS's • 4-1-4 Recording • 4-1-5 Release of IFR Aircraft • 4-1-6 Visits to Air Traffic Facilities • 4-1-7 Operation Take-off and Operation Raincheck • 4-1-8 Approach Control Service for VFR Aircraft • 4-1-9 Airports Without Operating Control Towers • 4-1-10. IFR Approaches/Ground Vehicle Ops • 4-1-11 UNICOM/MULTICOM Freqs • 4-1-12 UNICOM for ATC • 4-1-13 ATIS • 4-1-14 AFIS • 4-1-15 RADAR Traffic Service • 4-1-16 Safety Alert • 4-1-17 Radar Assistance to VFR Aircraft • 4-1-18. VFR Terminal Radar Services • 4-1-19 TEC • 4-1-20 Transponders • 4-1-21 Hazardous Area Reporting • 4-1-22 Airport Reservation Ops • 4-1-23 Requests for Waivers • 4-1-24 Weather Processor
4-2-1 General • 4-2-2 Radio Technique • 4-2-3 Contact Procedures • 4-2-4 Call Signs • 4-2-5 Leased Aircraft • 4-2-6. Ground Call Signs • 4-2-7 Phonetic Alphabet • 4-2-8 Figures • 4-2-9 Altitudes • 4-2-10 Directions • 4-2-11 Speeds • 4-2-12 Time • 4-2-13 Radio Inop Comm. • 4-2-14 VFR Comm.
4-3-1 General • 4-3-2 Towered Airports • 4-3-3 Traffic Patterns • 4-3-4 Visual Indicators at Untowered Airports • 4-3-5 Unexpected Maneuvers • 4-3-6. Use of Runways • 4-3-7 LLWS/Microbursts • 4-3-8 Braking Reports • 4-3-9 Runway Friction • 4-3-10 Intersection Takeoffs • 4-3-11 LAHSO • 4-3-12 Low Approach • 4-3-13 Light Signals • 4-3-14 Comms. • 4-3-15 Departure Delays • 4-3-16 VFR Flights • 4-3-17 VFR Helicopter Ops • 4-3-18 Taxiing • 4-3-19 Low Vis. Taxi • 4-3-20 Exiting the Runway • 4-3-21 Practice Approaches • 4-3-22 Option Approach • 4-3-23 Aircraft Lights • 4-3-24 Flight Inspection/`Flight Check' Aircraft in Terminal Areas • 4-3-25 Hand Signals • 4-3-26 Uncontrolled Airports With ASOS/AWOS
4-4-1 Clearance • 4-4-2 Clearance Prefix • 4-4-3 Clearance Items • 4-4-4 Amended Clearances • 4-4-5 CDR • 4-4-6 Special VFR • 4-4-7 Pilot Responsibility • 4-4-8 VFR-on-top • 4-4-9 VFR/IFR • 4-4-10 Adherence to Clearance • 4-4-11 IFR Separation • 4-4-12 Speed Adjustments • 4-4-13 Runway Separation • 4-4-14 Visual Separation • 4-4-15 Visual Clearing Procedures • 4-4-16 TCAS I & II • 4-4-17 TIS
4-5-1 Radar • 4-5-2 ATCRBS • AIM 4-5-34-5-3 Surveillance Radar • 4-5-4 PAR • 4-5-5 ASDE-X • 4-5-6 TIS • 4-5-7 ADS-B • 4-5-8 TIS-B • 4-5-9 FIS-B • 4-5-10 ADS-R
4-6-1 RVSM Mandate • 4-6-2 • Flight Levels • 4-6-3 Operator Approval • 4-6-4 Flight Planning into RVSM • 4-6-5 Pilot RVSM • 4-6-6 MWA • 4-6-7 Wake Turbulence • 4-6-8 Pilot/Controller Phraseology • 4-6-9 Contingency Actions • 4-6-10 Accommodation of Non-RVSM • 4-6-11 Climb/Descent to/from Flight Levels Above RVSM