INSTRUMENT FLIGHT RULES WORKBOOK
Ground control frequencies are provided to eliminate frequency congestion on the tower
frequency. They are used for issuance of taxi information, clearances, and other necessary
contacts between the tower and aircraft or other vehicles operated on the airport. Aircrew who
have just landed should not change from the tower frequency to the ground control frequency
until they are directed to do so by the controller. Normally, only one ground control frequency is
assigned at an airport.
At locations where the amount of traffic so warrants, another frequency, designated as a
clearance delivery frequency, may be assigned. If available, this frequency should be used to
request flight clearances; otherwise, use Ground Control for this purpose. ATC issues
clearances, and clearance delivery/ground control simply relays the clearance to aircrews.
Approach and departure control services are provided by an approach control facility for arriving
and departing aircraft and, on occasion, enroute aircraft. At some airports not served by an
approach control facility, the Air Route Traffice Control Center (ARTCC) provides limited
approach control services.
Air Route Traffic Control Center
ARTCCs are established primarily to provide air traffic service to aircraft operating on
Instrument Flight Rules (IFR) flight plans within controlled airspace, principally during the
enroute phase of flight.
Flight Service Stations
FSSs are air traffic facilities that provide pilot briefings, enroute communications, and VFR
search and rescue services; assist lost aircraft and aircraft in emergency situations; relay ATC
clearances; originate Notices to Airmen; broadcast aviation weather and National Airspace
System (NAS) information; receive and process IFR flight plans; and monitor NAVAIDs. In
addition, at selected locations, FSSs provide Enroute Flight Advisory Service (Flight Watch),
take weather observations, issue airport advisories, and advise Customs and Immigration of
Supplemental Weather Service Locations (SWSLs) are airport facilities staffed with contract
personnel who take weather observations and provide current local weather information to
aviators via telephone or radio. All other services are provided by the parent FSS.
Automatic Terminal Information Service (ATIS)
8-8 INTRODUCTION TO GROUND, AIRBORNE, LOST COMMUNICATION, AND
EMERGENCY VOICE PROCEDURES