Clearance Limits -Cont.

CHAPTER EIGHT

INSTRUMENT FLIGHT RULES WORKBOOK

When an air traffic clearance has been obtained under instrument flight rules, the pilot in

command of the aircraft shall NOT deviate from the provisions thereof unless an amended

clearance is obtained. The most important and guiding principle to remember is the last ATC

clearance received has precedence over related portions of any previous ATC clearance. It is

possible to change your flight plan while enroute; however, you must request and receive an

amended clearance prior to deviating from your original clearance. Should a pilot, for any

reason, be incapable of complying with any provision of an amended ATC clearance or

restriction, the pilot is expected to immediately advise ATC. A brief reason, such as "unable due

to fuel," may be included if considered necessary.

Upon arriving in the vicinity of your destination airport, you will be handed off to the Approach

Control serving the terminal airport. Approach Control will issue a clearance for an instrument

approach to your destination, depending on your intentions and the existing traffic in the area.

They may let you use an approach of your own choosing or they may assign you a specific one.

Normally the Approach Control facility will have extensive radar coverage of the terminal area.

They may use this radar for traffic advisory information or they may use it for a radar approach

to the field. Approach Control will handle all Ground Controlled Approaches (GCA) serving the

airport in their area.

The Terminal Radar Approach Control (TRACON)facility controls aircraft approaching and

departing airports, generally out to about 50 miles from the airport. A TRACON "sees" aircraft

using radar. A TRACON has responsibility for controlling specifically defined and limited

sections of "airspace." That involves ensuring that all aircraft entering or departing the airspace

are kept separated at safe distances. When necessary TRACONs reroute aircraft to avoid

dangerous weather patterns. A TRACON's total airspace is subdivided into small sections called

sectors. Each sector is assigned to an individual air traffic controller who works in the TRACON

facility. That controller directs the movement of aircraft in and out of that space on an individual

radar screen and maintains voice contact with pilots. Although the controller's individual

responsibility is only for his or her own sector, all controllers within a TRACON have full radar

information on all the aircraft that are under control of the entire TRACON facility. Because

they are colocated, these controllers are able to communicate with one another instantaneously,

something that contributes significantly to assuring the safety of aircraft.

Approach/Departure Control at Navy airfields normally consists of a Radar Air Traffic Control

Center (RATCC). This same type of facility at an Air Force Base is called Radar/Approach

Control (RAPCON). The following diagram shows air traffic over the United States during a

peak period and provides a link to the FAA for additional information.

8-16 INTRODUCTION TO GROUND, AIRBORNE, LOST COMMUNICATION, AND

EMERGENCY VOICE PROCEDURES