Tutorial
4. Local Control (Tower)
Controltowers were established to provide for a safe, orderly, and expeditious flow of air traffic at an airport and inits vicinity. It is hard to miss the Control Tower, the tall building with the glass-enclosed cab on top. Eachairport's control tower is also known as Local Control.
There are four major controller classifications at controltowers:
Controllers working in Local Control (an airport's controltower) are rotated through each position during one work shift. Each of these positions has specific duties.
Flight Data Controller
The Flight Data Controller:
IFR clearances are received and printed on a flight dataentry and printout (FDEP) device. Clearances are printed on forms using a standard format called flight progressstrips or flight strips.
Follow this link to learn moreabout a flight progress strip
The Flight Data Controller is also responsible for the AutomaticTerminal Information Service (ATIS) equipment. ATIS recordings are made every hour or more often if the weatherchanges.
Follow this link to
Clearance Delivery Controller
The Clearance Delivery Controller is responsible for obtaining and relaying departure clearances to pilots.
These departure clearances include the following information:
The Clearance Delivery Controller checks to see that theroute indicated for the flight requested conforms to established preferential routes. If there are departure restrictionsthat would supercede the requested clearance, then the clearance delivery controller may temporarily amend theclearance.
Ground Controller
The Ground Controller is responsible for the ground movement of aircraft taxiing or vehicles operating on taxiwaysor inactive runways. The ground controller is responsible for and can issue clearances only to those aircraft andvehicles that can be seen by this controller.
Runway Incursion prevention is a primary responsibilityof the ground controller. In the year 2000 there were more than 400 runway incursions recorded. A runway incursionis the unauthorized entry of an aircraft or vehicle onto an active runway without the permission of the local controller.
For a Ground Controller to issue a clearance for an aircraftor vehicle to cross an active runway, the ground controller must first gain permission from the local controllerresponsible for that runway.
Another major responsibility for the ground controller isprotection of "critical areas". These protected zones include localizer, glide slope and precision approachcritical areas. The critical areas provide greater obstacle clearance during approaches. As the weather conditionschange, the size of the zone increases. For example, if the weather conditions give a ceiling of less than 800feet with the landing aircraft between the outer marker and the runway, then taxiing aircraft and other groundvehicles must hold short of the designated critical areas until the aircraft has landed.
For approaches by "heavies" with the ceiling lessthan 200 feet or with the Runway Visual Range (RVR) at 2,000 feet or less, the critical area expands to an evengreater distance from the runway. The airport is responsible for determining size of the critical area and designatingthe affected runways and/or taxiways in their briefings.
Local Controller
The one major responsibility of the Local Controller is to provide separation between arriving and departing aircraft. Another major responsibility of the Local Controller is to safely sequence arrivals and departures. This controller also relays IFR clearances and taxi instructions. The Local Controller also issues takeoff and landing clearances and provides assistance to other flights flying through their local area.
Of course, there are regulations. The FAA has clearly identified guidelines for keeping aircraft at a safe distance from each other. This is known as safe separation distance. According to the FARs, runway separation regulations describe the following three aircraft categories:
The FAA separation regulations also specify that departingaircraft may not take off from a runway unless:
But the regulations also say that the following aircraftcan depart:
In other words, during the Takeoff phase of flight a fast, large jetliner should never take off behind a much smaller and slower two-seater aircraft until it is out of the way. A local controller can allow an aircraft in line for takeoff to "taxi in position and hold" in the run-up area while another aircraft is on its takeoff roll.
For arriving aircraft similar separation standards apply.IFR flights use a standard instrument approach when arriving at an airport. VFR pilots follow a standard trafficpattern. The VFR traffic pattern is an established, standardized flight pattern.
The separation regulations for arriving aircraft are similarto the departure regulations with added complications. All departing aircraft start with zero speed. Arriving aircrafthave different speeds with higher speed aircraft overtaking other slower aircraft. Many aircraft have stall speedshigher than many other aircrafts' top speed. The controllers must sequence and space all arriving aircraft in adynamic system.
A further complication is all aircraft produce wingtip vortices. Vortices are caused by generating lift from the wings. The vortices generated by a small aircraft are not nearly as troublesome as the vortices generated by a "heavy.""Heavy aircraft" (aircraft weighing 300,000 pounds or more) and Boeing 757 aircraft, generate vortices with a strength of small tornadoes. Wingtip vortices generated by a large jetliner can cause tremendous turbulence for a much smaller aircraft if it is following too close behind. There has to be a greater separation in distance and time when a "heavy" is in the traffic mix. Wingtip vortices can cause problems no matter the size of any of the aircraft if safe separation is not maintained.
Remember, it is the local controller who determines thespacing and separation of both departing and landing aircraft. Wingtip vortices and safe separation are extremelyimportant to the pilots of these aircraft and the local controller assisting them.
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