M ANAGEMENT S YSTEM
1.4 Airport Control Tower (TWR) Operations
The airport control tower (TWR) is where all flights begin and even tually terminate. The AoR of a TWR is an ATZ in the shape of cylinder, with 5–10 Nm radius and 2,000–10,000 ft height (ICAO 2007a). The functions of an TWR are normally performed by two control positions:
1. The airport or local controller (LOC), who is responsible for operations on the runway and all aircraft flying within the AoR of the control tower.
2. The ground controller (GRD), who is responsible for all traffic on the maneuvering area with the exception of runways.
Airport or tower (TWR) controllers issue information and clear-ance to aircraft in order to achieve a safe, orderly, and expeditious flow
Class E
Class G Class G Class G Class D Class G
Class C Class B
Class A
Figure 1.6 Classes of airspaces in the ATM system.
THE AIR TRAFFIC MANAGEMENT SYSTEM 19
of traffic in the vicinity of an airport with the purpose of preventing collision(s) between:
1. aircraft flying within the designated AoR of the control tower 2. aircraft operating in the maneuvering area
3. aircraft landing and taking off
4. aircraft and vehicles operating in the maneuvering area 5. aircraft in the maneuvering area and obstructions on that area ICAO (2007a) defines the maneuvering area as the part of the air-port that is used for takeoff, landing, and taxiing of aircraft, excluding aprons. ICAO clearly states that only the maneuvering area is within the jurisdiction of the airport controllers.
A simplified version of airport operations comprises six phases, as shown in Figure 1.7. In Position 1, a departing aircraft in the apron initiates a call, requesting an engine start-up. The ground control-ler normally approves the start-up except in cases where the aircraft is subject to ATFM restrictions or locally imposed restrictions (e.g., another unit may restrict the departure flow due to heavy workload).
From the same position, the aircraft is provided with taxi clear-ance information regarding the runway and weather information.
In Position 2, the departing aircraft is held at the runway holding position where the pilots accomplish the engine run-up procedures.
At this position, the ground controller transfers control to the local
Figure 1.7 Typical operations in airports.
Taxiway Taxiway
Apron 1
2 3 4
5
6 Runway in use
Downwind leg
Base leg
Final
2 0 COGNITIVE ENGINEERING AND SAFETY ORGANIZATION
controller who issues a clearance to the aircraft to enter the runway.
Subsequently, in Position 3, the local controller issues a takeoff clear-ance if not practicable in Position 2 (e.g., if there are conflicts in the arriving traffic on final). After the aircraft is airborne, the local con-trollers transfer control to the approach concon-trollers.
Control of airport traffic is based on visual observations of the maneuvering area and the vicinity of the airport. In low visibility conditions, a surface movement radar (SMR) can be used to augment visual observation of traffic in the maneuvering area and surveillance of traffic in those areas that cannot be observed visually. The duties and challenges faced by controllers and pilots in airport operations are briefly presented below.
1.4.1 Airport Controller Duties
The description of the duties of airport or tower controllers is based on the training and operational manuals of TWR units. The general duties of the local, ground, and delivery positions are:
• Ensure the integrity of the working position and use automa-tion tools as appropriate
• Issue inbound and outbound instructions to aircraft
• Obtain and issue IFR clearances to departing aircraft and ensure correct readbacks
• Ensure that flow management procedures are met
• Select runway in use
• Correctly handle aircraft and vehicles operating in the maneuvering area
• Integrate VFR arrivals and departures into the airport traffic circuit
• Issue flight information, traffic information, and appropriate airport information
• Coordinate with approach/area control and relevant airport operators
• Monitor flight data displays and ensure that they are kept up-to-date
• Use appropriate phraseology and transmitting techniques
• Transfer communication at predefined points
• Prioritize and delegate tasks when appropriate
THE AIR TRAFFIC MANAGEMENT SYSTEM 21
• Communicate with aircraft and colleagues in a clear and pre-cise manner
• Ensure that all coordination is in accordance with prescribed procedures
• Manage air-ground and ground-ground communication failures
• Assist and give priority to aircraft in unusual situations and take all actions necessary to ensure safety
1.4.2 Pilot Duties during Taxiing, Start up, or Landing
Upon arriving at the aircraft, the flight crew must complete a large number of tasks in a short period of time. One pilot normally sets up the flight deck while the other goes outside to check the aircraft and look for defects, bird-strike damages, and obstructions of the sen-sors and probes. The flight deck is set up for the particular departure including arrangements for standard instrument departure, levels, and frequencies. The flight management system (FMS) is programmed to receive feedback about fuel requirements, flight time, maximum flight level, take-off speed, and so on. Once the clearance to start up is received, the flight crew begins the departure briefing, which also covers responses to several unusual situations.
During the preflight stage, the flight crew is supplied with many data about the course of the flight (e.g., navigation waypoints, flight levels and associated speeds, and meteorological data). In addition, NOTAMs are distributed by means of telecommunication that contains information concerning the establishment, condition, or change of any aeronautical facility, service, procedure, or hazard that is essential to aviation practi-tioners (ICAO 2007a). Company and ATFM delays (e.g., slots and late arrivals) are taken into account at this phase. The flight crews perform basic weight calculations and decide how much fuel, passengers, and cargo they can afford. Fuel calculations must take into account several external factors, such as weather conditions at destination and the loca-tion of alternate airports. The crews need to verify that the aircraft’s final weight and balance remain within predefined limits before entering them into the FMS. At this stage, the ATC units are notified about the flight through the flight data processing system and about any ATFM measures imposed on the particular flight.
2 2 COGNITIVE ENGINEERING AND SAFETY ORGANIZATION
Once the engines are running and all after-start checklists are completed, a taxi clearance is obtained from the ground con-troller. In large airports, taxiing may take several minutes while proceeding though various taxiways and intersections may be a complex task that requires constant monitoring and coordination with ground controller. Both crew members are monitoring the taxi route and try to avoid the “heads down” syndrome in the cockpit.