Basic Air Traffic Control
The Air Traffic Control Mission
Air Traffic Control is a service provided to promote the safe, orderly, and expeditious flow of air traffic. The primary purpose of the ATC system is to prevent a collision between aircraft operating in the system and to organize and expedite the flow of traffic. In addition to its primary function, the ATC system has the capability to provide additional services. The ability to provide these additional services is limited by many factors, such as the volume of traffic, frequency congestion, quality of radar, controller workload, higher priority duties, and the pure phsical inability to scan and detect those situations that fall into this category. It is recognized that these services cannot be provided in cases in which the provision of services is precluded by the above factors. Consistent with the aforementioned conditions, controllers shall provide additional service procedures to the extent permitted by higher priority duties and other circumstances. The provision of additonal services is not optional on the part of the controller, but rather is required when the work situation permits. (Quoted per VATUSA policy.)
ATC Positions and Functions
Air Traffic Control services can be divided into two major subspecialties, terminal control and en-route control. Terminal control includes the control of traffic on the airport surface and airborne aircraft within the immediate airport environment. Terminal controllers work in facilities called control towers and terminal area control, also know as TRACONs. En-route controllers control the traffic between the terminals. They can also control traffic in and out of airports thwer the traffic volume does not warrant the establishment of a terminal ATC operation at that field. En-route controllers work at facilities called Area Control Centers or more commonly Air Route Traffic Control Centers, or ARTCC. Below is a basic summary of where each position is and what its primary function is.
Clearance Delivery (DEL)
The DEL controller is primarily responsible for ensuring that a pilots IFR flight plan is correct and legal for flight. The controller must verify thier filed route, ensure correct altitude for their direction of flight, and assign a proper transponder code to the aircraft. They also provide clearance for VFR aircraft out into and out of the Class Bravo airspace.
Ground Control (GND)
The GND controller is responsible for the safe and orderly operations of aircraft within the "movement" area of an airport. These areas generally include all taxiways, holding areas, and aprons. Any aircraft operating within these areas are required to have clearance from the GND controller.
Local Control (TWR)
The TWR controller is primarily responsible for the active runways. TWR clears aircraft for departure and landing, and ensures that the runways are clear and safe. Based upon local SOP and wind conditions, the TWR controller will determine which runways will be active. They are also responsible for all aircraft flying closed traffic at the field.
Approach Control (APP)
The APP controller controls all IFR aircraft within its portion of the Approach airspace. This airspace will also include any minor uncontrolled airfields within its airspace. APP provides vectors to the airport and issues approach clearances.
En-route Control (CTR)
CTR controllers provide ATC services to all IFR aircraft operating within controlled airspace.
Weather Information (METAR)
METAR (Aviation routine weather report) provide a detailed briefing of the current weather reported for an airport. At first look, the report can be quite confusing, so lets take a look at one and break it down.
METAR KMCO 121755Z AUTO 21016G24KT 1SM RA BKN015 OVC025 06/04 A2990
METAR
Type of Report. METAR - Hourly........SPECI - Special
KMCO
Four character ICAO identifier.
121755Z
Date and zulu time of the report.
AUTO
AUTO indicates automated report.
21016G24KT
This indicates that the winds are 210 at 16 knots with gust up to 24 knots.
1SM
This indicates that visibility at the field is reported to be limited to 1 statute mile.
RA
This indicates that rain is present at the field, there is a long list of different identifiers used to show local weather conditions.
06/04
Temperature and dew point in degrees celsius.
BKN015 OVC025
This is where we find the airport ceiling information. Clouds are reported broken at 1500ft and overcast at 2500ft.
A2990
This reports the altimeter setting for the field.
Refer to the chart below to reference the various qualifiers used in METAR reports.
VFR and SVFR Weather Minimums
VFR
Since VFR pilots fly by what they see outside and do not rely on the instrument panal, there are some restrictions as to when they can fly. The main restriction is the weather. As controllers, you should be aware of these restrictions and the current weather in your control area and apply them. VFR weather restrictions are as follows:
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Cloud base at or above 1000 ft AGL.
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Visibility at 3sm or greater.
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When flying VFR the pilot must remain clear of all cloud coverage.
Refer to the following chart to see how VFR requirements differ between the various airspace classifications:
Special VFR (SVFR)
SVFR is a procedure to let VFR pilots who are not IFR qualified to arrive and depart at an airport in Class B, C, D, or E surface area when the weather is below basic VFR minimums. The SVFR weather minimums are as follows:
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At least 1sm flight visibility for operations within Class B, C, D and E surface areas.
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At least 1sm ground visibility if taking off or landing.
The purpose of SVFR is to allow a pilot to depart an airport that is currently reporting weather below VFR minimus, but the weather is reported to be at VFR is close proximity of that airport. This is also to assist VFR pilots that are flying into an airport and the weather suddenly drops to below VFR minimums. These aircraft can request SVFR and complete thier flight without having to divert.
National Airspace Classification System
The national airspace system consist of a network of navigational aids and a number of air traffic control facilities designed to operate in conjuction with the various defined classes of airspace. These classes are subdivided into controlled, uncontrolled, special use, and other airspace catagories as outlined above.
Controlled Airspace
Controlled Airspace includes all airspace categorized as either Class A, Class B, Class D, or Class E airspace. While operating in controlled airspace, pilots are subject to certain operating rules as well as equipment requirements. In accordance with each airspace classification, ATC service is provided to aircraft operating under IFR and VFR.
Class A
This class includes the airspace over the United States and the airspace overlying the waters within 12 nautical miles of the coast of the 48 contiguous states, from 18,000 feet MSL up to and including 60,000 feet MSL, also known at Flight Level 600 (FL600). The FAA requires all persons operating an aircraft in Class A airspace to be flying under IFR. Operations in Class A airspace can only be conducted under an air traffic control clearance received prior to entering the airspace and each aircraft must be equipped with a two-way radio capable of communicating with ATC on an assigned frequency and an operating transponder.
Class B
The first of the two airspaces that surround busier airports. This class typically has two or more levels of airspace that are portrayed as a series of interconnected circular patterns around primary airports. Terrain, the amount and flow of air traffic, and the location of other airports all influence the design of Class B airspace. Generally, Class B airspace begins at the surface and extends vertically to 10,000 feet MSL surrounding the nation's busiest airports in terms of IFR operations or passenger enplanements. The floor and ceiling of each layer of Class B airspace are depicted on charts by MSL altitudes with each layer serving as a building block for funneling air traffic into the terminal area. Aircraft desiring to operate in Class B airspace must recieve clearance from ATC and their aircraft must have a radio, and an operable transponder with automatic altitude reporting equipment. IFR aircraft must have a VOR or TACAN receiver onboard. Below is the Class B airspace depicted for Orlando Internation Airport, KMCO.
Class C
The second of the two airspaces that surround busier airports. This class surrounds those airports that have an operating control tower serviced by radar approach control and facilitate a given number of annual IFR operations or passenger enplanements. Class C airspace is individually tailored for each airport; however, Class C airspace generally consist of a five nautical mile radius core area that extends from the surface to 4,000 feet AGL and a ten nautical mile radius shelf that normally extends from 1,200 feet to 4,000 feet above the airport elevation. The outer shelf usually extends out to 20 nautical miles from the primary airport. Aircraft operating within the Class C airspace must establish and maintain two-way radio communications with ATC prior to operations.
Class D
This airspace normally extends from the surface up to approximately 2,500 feet AGL and surrounds those airports with an operating control tower that does not provide radar service. This airspace is classified as Class D only when the tower is operational. Prior to operating within Class D airspace, pilots must establish and maintain communications with ATC.
Class E
This airspace consists of all controlled airspace that is not associated with Class A, Class B, Class C, or Class D airspace. This airspace is typically found around airports that do not have an operating control tower or en route airspace above 700 feet AGL or 1,200 feet AGL. The weather minimums a pilot must maintain when operating in Class E airspace is dependent upon whether they are operating at an altitude below 10,000 feet MSL or at or above 10,000 feet MSL. While direct communications are not required to operate within Class E airspace under VFR, aircraft desiring to operate under IFR must contact the area ATC facility for clearance information.
Uncontrolled Airspace
Uncontrolled airspace is designated Class G airspace. Typically, Class G airspace includes all airspace not classified as Class A, Class B, Class C, Class D, or Class E airspace. Whereas ATC services are provided with controlled airspace, no ATC services are provided within Class G airspace.
Communications
Radio communications play a major role in the ATC system. The proper phraseology enhances safety and is the mark of a professional controller. Below is the phoenetic alphabet recognized world wide by pilots and controllers.
Aircraft Identification
It is very important that you are able to clearly indentify an aircraft when issueing an instruction. Improper us of call signs can result in pilots executing a clearance intended for another aircraft. Controllers should not abbreviate call signs of an air carrier or other civil aircraft having authorized call signs upon initial contact. Abbreviated call signs may be used when appropriate after initial communications have been established.
Civil Aircraft
These are aircraft that typically have the traditional "N" number for a callsign. For example a Mooney with the callsign of N429R would be pronounced as "November four two niner Romeo". After communications have been established you could revert to "Mooney four two niner Romeo". Whats most important to notice is that the entire call sign in individually sounded out.
Air Carriers
These aircraft have a company prefix followed by a flight number. For example DAL427 is pronounced as "Delta four twenty-seven". The difference here is that the flight number does not have to be sounded out individually.
Altitude Pronounciation
The proper pharaseology in communicating altitudes to pilots is crucial. Below are some examples.
0 ft - 17,999ft
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12,500 "One two thousand five hundred"
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500 "five hundred"
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10,000 " one zero thousand"
Flight levels 18,000 and up
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19,000 "Flight level one niner zero"
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37,000 "Flight level three seven zero"
Altitude Assignments
Before getting into the flight direction rules it's probalbly a good idea to go over a few basic terms that every controller should know that pertain to altitudes and pressure.
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Altitude - The vertical position of an aircraft above Mean Sea Level (MSL).
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Flight Level - A standard nominal altitude of an aircraft. In the United States a Flight Level begins at 18,000 MSL.
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Transition Altitude - The highest altitude at which an aircraft in normal operations should use an altimeter pressure setting. In the US this in 18,000 MSL.
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Transition Level - The lowest flight level available for use above the transition altitude.
To ensure safe separations between aircraft above the transition level, flight levels have been allocated to aircraft according to their direction of flight. This system is known as the NEODD-SWEVEN rule.
NEODD - Aircraft flying North or East (0* to 179* Magnetic Course) will be issued odd altitudes up to and including FL410. Above FL410, aircraft will still be given odd altitudes yet at intervals of 4000 ft. (ie...FL450, FL490, FL530).
SWEVEN - Aircraft flying South or West (180* to 359* Magnetic Course) will be issued even altitudes up to and including FL400. Above FL400 aircraft will be given odd altitudes yet at intervals of 4000ft beginning at FL430 (ie...FL470, FL510, FL550).
VFR aircraft are supposed to follow the NEOOD-SWEVEN rule plus 500ft, but since the aircraft is VFR, altitudes are at the pilot's discretion.
