Coordination in Air Traffic Control Work The Copenhagen Fieldstudies
Johan Berndtsson [email protected] Maria Normark [email protected] Center for Tele-Information Technical University of Denmark WORKING PAPER: DO NOT QUOTE OR REFERENCE! However, feel free to comment! Johan Berndtsson & Maria Normark, Center for Tele-Information, Technical University of Denmark File: ATC-Copenhagen.doc, Saved: 98-12-03 13:22, Printed: 98-12-03 13:24
TABLE OF CONTENTS
INTRODUCTION ...... 1
RESEARCH METHODS ...... 2 I. AIR TRAFFIC CONTROL WORK ...... 4
AVIATION SERVICE IN EUROPE AND COPENHAGEN ...... 5 WORK ARRANGEMENTS IN COPENHAGEN AIR TRAFFIC CONTROL WORK...... 6 The Area Control Center (en route control) ...... 8 The Approach...... 9 The Tower ...... 11 The Apron Tower ...... 11 THE SKILLFUL USE OF PROCEDURES AND TOOLS ...... 12 II. THE FLIGHT STRIPS AND THE CLOSED CIRCUIT TV-SYSTEM...... 16
THE FLIGHT STRIPS ...... 16 Flight strips are tangible tools...... 17 THE CLOSED CIRCUIT TV-SYSTEM...... 19 Two simple scenarios...... 21 DAL123 departing from Copenhagen ...... 21 SAS987 approaching Copenhagen...... 22 COORDINATION THROUGH THE CCTV-SYSTEM...... 22 AFFORDANCES OF THE MEDIA...... 26 PAPERBASED OR ELECTRONIC FLIGHT STRIPS? ...... 28 CONCLUSION ...... 30 III. FUTURE WORK...... 32
REFERENCES...... 33
APPENDIX I: FIELDS ON THE FLIGHT STRIP ...... 36 Johan Berndtsson & Maria Normark, Center for Tele-Information, Technical University of Denmark File: ATC-Copenhagen.doc, Saved: 98-12-03 13:22, Printed: 98-12-03 13:24
INTRODUCTION "We need to reduce the (telephone) coordination, because it takes to much time and is a source of errors." This is a common statement from the air traffic controllers at Copenhagen Airport where we have done our field studies. What do they mean by that? How have they dealt with this problem in the past, and how will they deal with it in the future? In what ways does it affect the controllers’ work setting? These and similar questions related to coordination have interested us in our ethnographic field study of air traffic control work. As an air traffic controller it's your job to maintain safe and cost effective control of the airspace - to make sure that the aircraft are separated at all time, and that they are given an optimal route to keep cost and flying time at a minimum. Since most aircraft pass through more than one sector, there is also a need to be aware of the colleagues work and coordinating work with them. The ability e.g. to foresee what the situation in a specific sector will look like in the next 15 minutes is of extreme importance to the controllers, and can only be answered through suitable coordination between the actors involved. Air traffic control work is a highly complex, distributed and time-critical activity. In Copenhagen some 260 controllers, assistants and supervisors are involved in the process of controlling aircraft in Danish airspace, i.e. the Copenhagen Flight Information Region (FIR). The controlling is being done from several different locations, ground control from the apron tower, tower control from the tower, Terminal Maneuver Area (TMA) control from the approach, and en route control from the Area Control Center. About one thousand aircraft are taking off and landing at Copenhagen airport each day, and about five hundred other aircraft passing through Danish airspace. Within and between these 'control rooms', controllers and assistants are working together to make the complex activity of air traffic control work safe and efficient. The time-critical aspect also makes for a large difference between ATC work and for example accounting, or design work. If the designer stops working for a few minutes her sketches will 'freeze', nothing will happen, but if the controller will stop working for a few minutes the situation in the air will not freeze, but continue to change. ATC work, as well as other time critical work, is thus 'paced' by this continuos change (Schmidt, Forthcoming-b). To overcome the difficulties descending from this geographical separation, and to facilitate the coordination of actions, air traffic control work is heavily supported by different procedures, each with it’s specific functions and areas of use. E.g. the division of airspace into sectors allowing a division of responsibility between controllers, agreements between sectors stating when and where certain activities will take place etc. The many and highly specified procedures serve as a resource in that the controller always knows e.g. where to expect a certain flight, what flight level (altitude) it will have etc. The reliance on procedures gives the controller time to deal with telephone-coordinated changes and unforeseen situations when they arrive. However, there is always a risk that something is not done in accordance with the procedures, and that this, in itself, poses a threat in case the controller is expecting e.g. the entering flight to be handed to him as agreed, and it’s not. But then again, if there was less, or no, procedures or rules to enable the anticipation of a situation, it would not is possible to control the amount of aircraft travelling through the airspace today.
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In many situations the work of the controllers is not only supported by procedures but also by different artifacts. Some of these are aimed at enabling the controllers to be aware of the current situation in the sky, such as the radar. Others are designed to reduce the time it takes to perform specific tasks, such as the speed dial panel for the telephone on the controller's positions. However to cope with the distributed settings described above there are also artifacts specifically designed to facilitate coordination of the controllers' activities in the different control rooms. An example of such an artifact used at Copenhagen Airport is the flight plan database and it's printouts (the flight progress strips), and the Closed Circuit TV (CCTV) system used to selectively display parts of controllers workplace to other controllers. The use of these tools is however also supported by procedures and practice, e.g. regarding the signs that are written on the flight progress strips, and, what activities that can be coordinated through the CCTV-system.
RESEARCH METHODS The results presented in this report are based on ethnographic field studies, primarily consisting of informal interviews and participatory observations. About 20 interviews have been conducted, with several different groups involved in air traffic control work, e.g. controllers, supervisors, assistants, and technicians. The interviews were recorded on audiotape. Informal interviewing was chosen mainly because it offers a significant benefit compared to more structured interview techniques in that very few assumptions regarding what is important in the work studied are made at an early stage. By discussing with, rather than interviewing, the informant about his or her work, the idea is that the researcher will learn what aspects of the work that are important, and therefore need further inquiry. By using a few very general questions, such as 'what does an air traffic controller do?', and 'what constitutes a good controller?', we 'steered' the interviews into topics of interest. Of course, the degree of details in the questions increased with our knowledge about the domain. We also tried to keep the number of interviews per day to two or less, to ensure that they were analyzed as soon as possible, both to avoid piling work and thus forgetting much about the interview, and to be prepared with complementary questions for the following interviews. Beside these interviews we have also had numerous spontaneous discussions with controllers, assistants and supervisors during our studies at Copenhagen airport. The interviews were generally followed by participant observation sessions lasting between one and three hours each. During a majority of the observation sessions the informant has been asked to continuously tell the researchers what s/he is doing during her/his actual work. Many of these initial observations have thus been conducted with a high level of interaction between the researchers and the informants. Doing ethnographic field studies is a constant iterative process. You go there, watch, listen, discuss, go home and listen to the tape, and from the listening you find more questions that you try to cover during the next session. It is also important to establish a close relation to the informants, to build up a trustful relationship. In our work we feel that we have been very lucky in this aspect. Not only have we had full support from the management, providing us with different kinds of documentation as well as encouraging the controllers to help us in our studies, the controllers themselves have also been very helpful. In order to get the answers you need, you have got to have good relations to people, and they have to feel confident in
2 Johan Berndtsson & Maria Normark, Center for Tele-Information, Technical University of Denmark File: ATC-Copenhagen.doc, Saved: 98-12-03 13:22, Printed: 98-12-03 13:24 you and your work. Some of the staff, especially from the controllers and the technicians, who we feel that we have come close to, has invested a large amount of time and patience in our work. In an area as complex as air traffic control this can literally take forever. However, after doing the initial interviews and observations, we felt that we had a sufficient overview to be able to focus on some more specific aspects of air traffic control work. For the rest of our study we chose to focus on different artifacts, trying to find out what role they play as supporting tools in the coordination work of the air traffic controllers situated in different locations. Through focussing on a set of artifacts and the way in which they are used in the work of the controllers, instead of on a specific role or a specific situation, we have tried to narrow our scope in a way that we believe is effective when time is limited, as it very much was in our case. In order to capture some of the details of the work with these artifacts, we also used video camera recordings for several of our observations. Filming in a quite dark and crowded area like an ATC-center is quite difficult. We experienced some problems with camera angles, and different angles proved to be useful in different situations. Due to the layout of the control room the alternatives for placing the camera were also quite limited. We also had some problems with the sound, but largely solved this by either placing the camera close to one of the loudspeakers playing the communication between the pilots and the controller, or by holding a handset playing the same communication close to the camera microphone. To analyze the collected data we have indexed and written summaries of the interviews and videotapes, and transcribed sections of central importance to our project. Complementing questions from interviews and observations were handled through repeated visits, but also through E-mail, fax and telephone communication with some of the air traffic controllers. These studies have also included studies of manuals, technical drawings and specifications, as well as academic books, reports and papers on air traffic control, such as the work of Hopkin, Halverson (Halverson, 1995)1 and the Lancaster CSCW group (Hughes et al., 1988; Harper et al., 1989a)2, and a substantial body of literature on relevant aspects from the field of CSCW.
1 See also (Halverson et al., 1992; Halverson, 1994b; Halverson, 1994a). 2 See also (Harper et al., 1989b; Bentley et al., 1992; Hughes et al., 1992; Sommerville et al., 1992; Harper and Hughes, 1993; Hughes et al., 1993; Harper et al., 1994; Hughes et al., 1994; Shapiro et al., 1994; Sommerville et al., 1994).
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I. AIR TRAFFIC CONTROL WORK Air traffic control work is about maintaining safe and cost-effective air traffic. This is done through keeping the aircraft separated from each other by talking to and giving instructions regarding height, speed and route to the pilots, as well as giving them information about weather conditions etc. Or as one of the controllers described his work: "I make sure that the aircraft that are going to take off and land get the most appropriate route, height, most cost effective, fastest, provided the safety is uncompromised." (ATC Officer in Copenhagen ACC) Although it may be self-evident, it is important to point out that the safety is the first and foremost concern of the controllers. However, route and flight level changes are not only made for safety reasons, they are often being done as a service to the airlines, allowing the pilot to get a faster or more economic route, e.g. to go directly to certain way points, or to get a more favorable altitude. Safety in air traffic control to a large extent means keeping the aircraft separated from each other. This can be done either by differences in altitude, i.e. flight level separation (minimum 1000 feet apart), or through separation in distance, lateral separation (three or five miles apart depending on the location of the aircraft). Keeping aircraft separated might seem as an easy task, but given the amount of traffic traveling through Danish airspace every day the work is quite complex, and it is controllable only through the skills of the controllers and an extensive use of conventions, procedures and tools. Without these a lot of negotiation and information coordination would have to be done. For starters, by dividing the air space into sectors, geographical areas, the work is organized in manageable pieces. The Danish airspace consists of nine en route sectors, divided into four upper and five lower sectors (see Figure 3, page 8). Each sector is manned with one or two controllers, one radar controller who is watching the radar and talking to the aircraft through the radio, and one planner controller who manage the strips and talk to adjacent sectors (as well as handling other phone calls), and a sector assistant. If there only is one controller, s/he is both controlling the radar and managing the strips. Air traffic control is a task of surveying and managing the sky. It is however also about coordinating work with others. Since most aircraft pass through more than one sector the work done by controllers in adjacent sectors is also of interest to the controllers. This also means that the work done in adjacent sectors has to be visible to the controller, and thus enabling the controllers to both plan their work ahead, and see how they best should hand over the traffic to the following sector controller. In the following section, Aviation Service in Europe and Copenhagen, we describe the context of air traffic control. Thereafter we will sketch an outline of air traffic control work, starting with describing the work organization in the section Work Arrangements in Copenhagen Air Traffic Control. There are also rules, on which they to an enormous extent are depending on, and tools that facilitate their work in all sorts of ways. We will describe it in further detail in the section The Skillful Use of Procedures.
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AVIATION SERVICE IN EUROPE AND COPENHAGEN By focusing on the relations between the different organizations involved in the process of producing air traffic we will in this section give an overview of the context in which air traffic control work is embedded. Our purpose is to provide a background to the more specific discussions regarding the coordination of air traffic control work presented in the following chapters. We have chosen to call this section "Aviation Service" to emphasize that air traffic control is part of a greater activity that largely affects the way in which the work is carried out. Air traffic control work is one of several activities involved in producing or supporting the production of, airborne transportation of people and goods between geographically separated places. There is an extensive network of organizations involved in the production of flights and there is also an extensive amount of rules and regulations that shape the activity. The organizations involved in the actual flying are the airline companies, Eurocontrol3 (the European organization for the safety of air navigation), the Danish Civil Aviation Administration (Statens Luftfartsvæsen), and the airport. Each of these three groups has different tasks to perform within this activity, as well as different purposes and goals with their participation, but they share however the interests of 'producing' efficient air traffic. The first step to 'create' a flight is taken by the airline company, e.g. Scandinavian Airlines, British Airways, who writes a request for a specific flight. The request includes information on where and when the flight is going to take place, as well as wishes regarding how the flight is to be executed, what route, altitude etc. that the aircraft will utilize on its journey. Once completed, the flight plan is submitted for inspection to Eurocontrol's Central Flow Management Unit4 (CFMU) in Brussels, Belgium. The flight plans are then sent to the Danish CAA, responsible for among other things the air traffic control in the Danish airspace, to be imported into the Danish flight plan database system. For the actual execution of the flight the airline companies of course also have to provide pilots, suitable aircraft, and customers for their flight. They also need several, in our case more peripheral services, such as cleaning, catering, maintenance etc. Another important issue in the execution of the actual flight is the airport. In order to be able to provide a high level of service with e.g. baggage handling, and to maintain buildings and runways etc. Copenhagen Airport charges the airline companies for their services, e.g. per minute they are on ground and for renting gates.
3 Eurocontrol was 1960 for the purpose of overseeing upper airspace air traffic control for the member states. Today Eurocontrol plays a central part in the development of new air traffic control systems in Europe. (Eurocontrol, 1998) 4 "The CFMU is responsible for providing ATFM services within the airspace of participating European States. Its main objectives are to develop and maintain the highest level of quality service possible to both its Air Traffic Services (ATS) users (provision of flight plan data, best use of available capacity, smoothing of traffic and protection against overloads) and its Aircraft Operators (AO) users (advice on flight planning, minimisation of penalties due to congestion) within the agreed ATFM policy and principles." (Eurocontrol, 1998) (ATFM is short for Air Traffic Flow Management)
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WORK ARRANGEMENTS IN COPENHAGEN AIR TRAFFIC CONTROL WORK As we briefly described earlier, the en route airspace is divided into geographical areas, or rather volumes of air, called sectors, in order to distribute the work among the different controllers. The Danish airspace, Copenhagen FIR (Flight Information Region), is divided into nine sectors, four upper and five lower. But there is also another division that has shaped the way that the work of controlling is arranged. The traffic controlling of the Danish Airspace from the Copenhagen Control Center can be divided into four different controlling units: 1. The Danish en route airspace is handled by the Area Control Center (ACC). It is divided into nine sectors, four upper, and five lower. 2. The Terminal Maneuver Area (TMA, or 'the approach area' which is the term used at Copenhagen Airport). This area is used for approaches to, and departures from, the airport (for Copenhagen Airport approximately the size of Shetland), and is managed by the Approach Control. The area is divided in two, one W/N (West/North) and E/S (East South) area. 3. The airspace immediately around the tower, and also the runways, are handled by the Tower control. The area is used for controlling take off and landing of aircraft. 4. The ground around the runways, e.g. the taxiway, the parking space, etc. is handled by the Apron Tower. It is likely that an aircraft crossing Danish airspace will pass several of these sectors and thus be controlled by several different controllers on the way.
Flight Level or Meters above Sea Level
FL 240
1500 MSL Ground
Apron Tower Approach ACC Distance from airport Tower
Figure 1: A departure from Copenhagen Airport showing the hand over moments between Apron Tower, Tower, Approach, and ACC (en route) control. All these different departments are located in different places. The Apron Tower has a building (a tower) of its own, located close to the gates to enable the staff to see some of the gates through the window. The tower is also in a separate building (a tower), overlooking the
6 Johan Berndtsson & Maria Normark, Center for Tele-Information, Technical University of Denmark File: ATC-Copenhagen.doc, Saved: 98-12-03 13:22, Printed: 98-12-03 13:24 runways. The Approach control and the ACC actually share a building, a large room, but they are sitting in different parts of this room (see Figure 2, page 6).
Figure 2: Sketch showing the overall layout of the Copenhagen ATC Control Room. The Tower and the Apron Tower are located in other buildings. Within each of these four 'departments' people have different roles and are assigned to different tasks. An Air Traffic Controller has the executive responsibility for handling the air traffic in the organization. By graduating as a controller, you are certified to work as an air traffic controller. However this is still highly restricted by rules regarding the maintenance of the skills, e.g. if a controller does not work with controlling for a longer period (a minimum of 20 shifts during a three month period has to be done) they have to be supervised for a certain period of time in order to get the certificate back. Another interesting aspect is that the controllers retire at the age of 55. Since air traffic controlling is highly demanding, the day is divided into shifts, which are divided into spells in about one hour each. This means that except from communicating with the colleagues, the controllers also have to keep the records, such as flight progress strips, notes regarding problem with equipment etc. up to date, to make the situation easy to understand for the controller taking over. Another group is the assistants. They have to know a lot about ATC work in order to be able to support the work of the controllers, but they have no certificates for controlling aircraft themselves. Supporting the controllers’ work can mean to prepare information, such as ‘pre- managing’ flight strips, or helping the controller to make certain phone calls etc. The Supervisor is responsible for the Air Traffic Control Center, i.e. ACC, the Approach, the Tower, and the Apron Tower. Supervisors are often retired air traffic controllers. Their task is basically to make sure every position is manned. They have no certificates to work as controllers any longer. The Flow Manager (a position staffed by the same personnel as the Supervisor position) administrates the workload that can be managed based on how many aircraft that are allowed
7 Johan Berndtsson & Maria Normark, Center for Tele-Information, Technical University of Denmark File: ATC-Copenhagen.doc, Saved: 98-12-03 13:22, Printed: 98-12-03 13:24 to enter Copenhagen FIR. This is done in cooperation with Eurocontrol, the European organization for air traffic control, in order to internationally plan traffic to avoid bottlenecks. There are also military controllers, officers, which are located at the Area Control Center at Copenhagen Airport. The military and civil air traffic control is done as a joint effort in Denmark.
The Area Control Center (en route control) The Area Control Center (ACC) handles flights when they are en route. Both halves are also divided into an upper and a lower airspace at flight level 245 (that is about 8000 meters). There are 4 upper sectors and 5 lower:
Figure 3: The upper (N, V, C and A) and lower (F, L, E, D and B) en route sectors in Copenhagen Flight Information Region (FIR).5 There is only one Area Control Center in Denmark and it's located at Copenhagen Airport. Approximately 90 air traffic controllers and 60 assistants are working shifts to keep the traffic passing through the en route sectors safe. This center is divided in two parts, ACC West and ACC East (see Figure 2, page 6). The staff in each sector is consists of at most one radar controller, one planner controller and one assistant. The radar controller is the basic position. S/he sits in front of the radar and is talking on the radio to the pilots. S/he is responsible of the radio frequency of the sector. The planner controller handles all coordination that have to be made in the sector, such as e.g. negotiating a more suitable flight level with the adjacent sector future responsible for the flight, or receiving information about changes that is not entered in the flight plans. S/he also arranges the strips to detect conflicts and make the radar controller aware of these before the situation gets critical. The assistant receives the first notification messages of the incoming aircraft in the sector, and prepares them and coordinates possible errors before the strip has come into the sector.
5 Picture taken from the Local Air Traffic Services Manual, Copenhagen. (Lokal ATS-Instruks ACC, IV Del, Kapitel 1, Kort 1. Version 6:th of November 1997.)
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The Approach The Approach control is handling an area of the size of, from the immediate area over the airport up to flight level 195 (19.500 Foot, approximately 6.500 meters). The function of the Approach sector could be seen as that of a funnel, where the ACC are pouring arriving traffic into the funnel from above. Within the funnel the controllers order the traffic into one steady stream. This ordered stream of traffic is then delivered to the Tower controllers. The airspace in the approach sector is divided into two parts, one W/N (West/North) and one E/S (East/South), and there is also a small area called Final.
W/N airspace
Final airspace
ILS signal Wind direction
Aircraft
E/S airspace
Figure 4: The division of airspace in the Approach sector, W/N, E/S and Final airspace, as viewed from a radar screen. The W/N and E/S controllers receive aircraft at their respective inbound way points, lines them up in two queues, and hands them over to the Final controller, who merges the two lines into one and hands them to the Tower. There are standardized landing procedures to land at Copenhagen Airport (STARs, Standard Arrival Routs), which every approaching aircraft has to follow. In these STARs, certain navigational way points, so called inbound way points, have been specified as entry points into Copenhagen Approach. The controllers working in the APP W/N sector handles aircraft coming in over the inbound way points SVEDA, TRANÅ and KORSA, and the controller in the APP E/S sector handles arrivals from CORSA and ALMA. Their job is then to line these aircraft up in one downwind6 stream from W/N and one from E/S, and hand them over to the final controller. This hand over is performed by the W/N or E/S sector controller asking the pilot of the aircraft to "contact final" at a specific frequency, and hands the flight strip over to the final controller who, as shown in the figure, sits between the controllers who handle the two approach sectors. The Final controller thus handles aircraft from both sectors and leads them up in their two respective queues to a point where they can turn (i.e. he orders
6 Aircraft has to land against the wind. Downwind means with the wind, and lining them up in this seemingly wrong direction gives the Final controller the time to arrange the two streams of aircraft by turning the aircraft towards each other, merging the two lines into one.
9 Johan Berndtsson & Maria Normark, Center for Tele-Information, Technical University of Denmark File: ATC-Copenhagen.doc, Saved: 98-12-03 13:22, Printed: 98-12-03 13:24 them to turn), be merged into one queue - not unlike the way a zipper works. Or, as expressed by one of the controllers: "You make sure they get in, they are… who is number one, two, three, four, five etc. etc. They are interplaited, and finally thread like pearls on a string, ready to land on for example runway 22 left." (Interview with ATC Officer at Copenhagen Approach, 1998-05-19) Once lined up the pilots can find the ILS (Instrument Landing System) signal and use the Instrument Landing System to land. Once established on the ILS the Final controller orders the pilot to contact the tower controller and the aircraft is thereby handed to the tower. Most of the time only one controller respectively handles the work in APP W/N and APP E/S. But, when the workload is heavy, the work with W/N and E/S respectively will be split up into two different roles, one handling departing aircraft and one handling arrivals. The basic positions, the ones that are used if only one controller is working the sector, are the ones closest to the left and right of the Final position. They are also the ones from where arriving aircraft are always controlled.
App W/N App W/N (Departure) (Arrivals) FINAL
App E/S (Arrivals)
App E/S (Departure)
Spare position
Coordinator
Figure 5: The work arrangements in Copenhagen Approach. The Final controller is sitting between the controllers handling arriving traffic, a position that enables verbal as well as non-verbal communication. This arrangement has lots of benefits since the workplace is designed to have the controllers who need to coordinate their work close to each other. E.g. as mentioned, the Final controller always have the controllers handing him aircraft next to her or him, facilitating the possibilities for both verbal and non verbal communication. And since the Final controller has nothing to do with departing aircraft, expanding the positions with departure controllers placed away from the Final controller, but close to the controllers handling arriving aircraft in
10 Johan Berndtsson & Maria Normark, Center for Tele-Information, Technical University of Denmark File: ATC-Copenhagen.doc, Saved: 98-12-03 13:22, Printed: 98-12-03 13:24 the same sector, works fine, since it enables the same kind of communication between the arrival and the departure controllers. The controllers in the W/N and E/S positions are also handling the departing aircraft, which later on will be handed from one of the controllers handling departures in the Approach control, to the en route sectors in Denmark and Sweden. Similarly to the approaching aircraft STARs, the departures are predefined through SIDs (Standard Instrument Departures), precisely defining the way in which each departure will be performed. There is also a third role involved in the work with approaching and departing aircraft, the Coordinator. The coordinator's main task is to support arrival and departure and give airway clearances (basically formal allowance to the pilot for the flight) to the two minor airports in the area, Roskilde and Værløse. S/he is also taking phone calls regarding some of the changes in altitudes and routes for approaching aircraft. These messages are then passed on through either talking out loud to the concerned controller, or by going over to the controller and make changes to the controller’s strips while briefly informing her or him about the new situation.
The Tower The Tower controllers and assistants handle the take offs and landings on the three runways at Copenhagen airport. The controlling work is basically divided between two controllers, in aircraft taking off and in aircraft landing. There is also an assistant, supporting the controllers by answering the phone, preparing the flight strips and coordinating changes with other involved parties through the telephone. The landing controller is responsible for the separation of the aircraft after they have been handed from the approach controller. Basically this means to make sure that the ‘first’ aircraft has left the runway before the next one is landing. S/he also has to make notes of call sign, aircraft type, runway, and the exact time of landing. This information is later passed on to the airport organization to be used for billing purposes. There are no strips for arriving aircraft in the tower, instead they follow the order presented through the Closed Circuit Television monitor, which shows the flight strips from the ‘final’ position in the Approach department where a controller is lining up the aircraft for landing. Each aircraft has it’s slot-time, a time period of 15 minutes within which the aircraft has to take off. If the slot is missed, a new one has to be requested, a process which in busy periods of the day can result in severe delays. When the pilot of an aircraft is ready to start, s/he calls the tower and requests a so-called airway clearance, permission for the flight to commence. If granted, the aircraft leaves the gate, and heads for the runway. When is entering the runway, he is instructed by the assistants in the Apron Tower to change radio frequency to the departure frequency, and is thereby shifted to the departure controller.
The Apron Tower The staff in the Apron Tower, which consists only of assistants, handles the aircraft on the ground, beyond the runways. They work closely with personnel from the airport, who organize the parking space in the gates. The main task of the ATC assistants in the Apron Tower is to communicate with the aircraft in the area before the runways, i.e. where all aircraft park at the gates, and to give taxi clearances (permission to reverse). The work is
11 Johan Berndtsson & Maria Normark, Center for Tele-Information, Technical University of Denmark File: ATC-Copenhagen.doc, Saved: 98-12-03 13:22, Printed: 98-12-03 13:24 similar to that of other departments in that they are trying to keep the aircraft from colliding, and in that they keep radio contact with the aircraft. The aircraft should be handed over to the receiving controller/assistant before the aircraft crosses the maneuver area border (the runway area). The Apron Tower staff also communicates with vehicles, e.g. busses for transporting passengers, driving in the area in order to avoid collisions. The normal arrangement for the radio in air traffic control is that all aircraft in the sector hear the communication on the radio frequency. In this case the Apron Tower differs a bit, because they have two frequencies, one for the aircraft and one for the other vehicles in the area. In the current work arrangement only air traffic control assistants work in the Apron Tower. However, there is also an assistant position in the Tower and formally they belong to the same part of the organization which means that a tower/apron tower assistant alter shifts between both places. Since there is a larger responsibility for the assistants to work in Apron Tower, it has been discussed to give them certain certification in order to be able to make their own decisions, when working in Apron Tower, instead of calling the controllers in the Tower, which is the current arrangement.
THE SKILLFUL USE OF PROCEDURES AND TOOLS To deal with the complex and time-critical work of controlling, the controllers rely on an extensive amount of procedures and tools. Well-applied procedures reduce the amount of time that would otherwise be spent negotiating with adjacent sectors, pilots and other people. We have previously mentioned the division of airspace into sectors as a way of enabling a structured way of handing over aircraft between sectors, but there are many others. During the three years that the air traffic control students spend in school, a lot of their time is devoted to learning rules, and practicing the application of them on simulated air traffic. Between every sector there are agreements regarding standard hand over Flight Levels, standard entry way points, etc. In short, there are standard procedures for almost everything, and in the way they are used within air traffic control work they can in many cases be seen as silent coordination between controllers – they know what to expect, where to expect it, and how to handle it, thanks to procedures. However, procedures do not solve everything. To cope with the situation, and to allow less silent coordination between controllers, air traffic control work involves many different artifacts to enable communication and coordination between the involved parties. One of the controllers’ most important tools is the radio equipment. They use it to tell the pilots of the aircraft in their sector which course to follow, which flight level to use, to hand an aircraft over to the next sector (asking the pilots to change frequency to the next sector’s frequency), and many other things. Each sector has its own radio frequency. To know for whom the message is meant, a unique ‘call sign’ is called out before the message. A call sign consist of the abbreviation for the specific airline company, and a specific flight number, e.g. BAW123 (British Airways, or ‘Speedbird’ as the controllers call all British Airways aircraft, flight 123). Within each sector, all aircraft tuned in on the sectors frequency can listen in on the communication. One benefit from this ‘open frequency’ is that all aircraft can hear warnings about e.g. thunderclouds or turbulence coming from other pilots. There are however also problems with this overhearing. One problem can be exemplified with the
12 Johan Berndtsson & Maria Normark, Center for Tele-Information, Technical University of Denmark File: ATC-Copenhagen.doc, Saved: 98-12-03 13:22, Printed: 98-12-03 13:24 airline Scandinavian Airlines (SAS), which has many flights in the Copenhagen region. When calling for a SAS flight it quite often happen that the pilots doesn’t answer, and the controllers’ explanation to this is that there simply are so many SAS flights, that sometimes a pilot doesn’t notice that it’s actually her or him the controllers are calling. This has since long been, and still is, a source of irritation among the controllers. Another thing worth noting is that there never is more than one controller per sector communicating (speaking) on the sector’s radio frequency. When talking on the radio, the phraseology used by pilots and controllers is very strict. There must be little, or no, confusion about the meaning of the messages sent on the radio. All conversation takes place in English, but with a very distinct pronunciation of the letter ‘r’. The phrases used in this radio communication have, in a way, been specially designed to increase interpretability of the messages through sometimes-noisy radio channels. For example, words that can easily be confused with each other, such as five and nine, have been changed into five and niner, to minimize the risk for mistakes. Another tool the controllers use in their work is the telephone, in order to coordinate activities with other sectors. To reduce the time it takes to dial the numbers, the dial-panel has been accompanied with a speed-dial panel with one single button for all of the most common numbers the controllers’ needs to dial, such as buttons for the different en route sectors, the Towers (both in Copenhagen, Roskilde and Værløse), Malmö ACC etc. An interesting aspect when it comes to the telephone is that the controllers, according to the rules, have to make a phone call to all other people he talks to, even if they sit right next to her or him. The reason for this is that all phone calls and radio traffic are recorded, so that if something happens, one can see what actually happened. This rule is however not followed. Sometimes it’s just quicker, or easier, to say something face-to-face (or rather ‘cheek-to-cheek’ as the controllers seldom look at each other while they are talking, but rather keep their eyes on the radar), or to shout it, and one controller said that it would feel very strange to call someone who sits right next to you. It also seems much of what is being said is not formally necessary, but are simply things they tell each other to be helpful, and they are often told when the controller is not in the middle of something since the controller next to her or him can see when it’s appropriate to pass the message. Receiving a phone call however, often means that you have to interrupt your current work to answer the phone. An interesting issue regarding the radio, the telephone, and verbal communication face-to- face, is that according to the controllers, these forms of coordination are the most time consuming ones, and the largest source of misunderstandings. Therefore an important issue when it comes to technological support for coordination is that they have to convey, in an almost minimalist way, only the right information. Therefore, supporting coordination in time-critical work environments through ‘making all needed information available at any time’ is not a good strategy. The radar screen, or Plan View Display (PVD), is also an important tool in air traffic control work. To get an overview of the air space or sector in question, the controllers study a radar screen.
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Figure 6: A photo from a PVD in the Approach. In the boxes, representing the position of the aircraft, a letter is written, showing which sector that currently controls which aircraft. E.g. SAS206 is currently controlled by sector W (Approach W/N). The picture on the screen is based on two sources; the seven (soon to be eight) radar beacons in Denmark and the information in the database with the flight plans. Each aircraft has a transponder that answers to the signal sent from the radar. The transponder sends a four-digit number – a so-called transponder code, which each plane is allotted before take off. It also sends information about its current altitude. Since the transponder code is entered in the flight plan database, the information in the two sources are correlated and a label consisting of data from both sources, such as call sign and actual flight level, will be shown next to the little square indicating the aircraft on the screen. The little square indicating the aircraft on the screen contains a letter, which represents the sector currently in control of the aircraft. Yet another important tool that the controllers use to keep track of each flight and the information about it are the flight strips. The flight strips will be explained in more detail further on, but they are basically a printout, showing the information available on the flight stored in the database, e.g. call sign, type of aircraft, departure city and arrival city, route and so on. The flight strips are used very actively, although the way in which they are used is highly restricted. As they among other things are used as up-to-date 'note books' for each flight the information on the flight strips, and especially the hand-written information, is of great importance to the adjacent sectors – and available to them through the Closed Circuit Television system. The controllers also have access to different info-systems to get information about weather conditions and other information needed. These are both available in paper and on computer screens. Nevertheless, there is of course more to it than procedures and tools. Procedures need to be applied, and tools used, in an intelligible manner for the work to be performed efficiently. Without the skill of the controllers neither the procedures nor the tools would be of much use. The message "approach morning, scandinavian seven niner one, information romeo, DC niner, flight level one two zero" from a pilot entering the approach area at Copenhagen
14 Johan Berndtsson & Maria Normark, Center for Tele-Information, Technical University of Denmark File: ATC-Copenhagen.doc, Saved: 98-12-03 13:22, Printed: 98-12-03 13:24 airport, or a VA -mark on the flight progress strip, is hard to interpret for people unfamiliar with ATC work. The skills of the controllers also include handling situations that has not been foreseen by the designers of the procedures and artifacts, and that thus have to be dealt with outside the system, or by manipulating it to suite the needs arisen in the specific situation. An interesting issue regarding the skill of the air traffic controllers is that they often know things that it is impossible to learn by reading, things that has to be learnt by experience or through discussions with more experienced controllers. One example of such knowledge is which kind of service to provide to which airlines, and how to foresee the traffic not only looking at speed, route and aircraft type. Different airlines have different policies. Some airlines emphasize being fast and efficient, even if this means that the flight will be more expensive, while other airlines always choose economy before speed. During our studies several air traffic controllers have talked about the way in which these policies affects the pilots' 'flying style', and thus also the way in which they are best managed, or served, by the controllers. However trivial it may sound this knowledge is important to the controllers when they give instructions to the aircraft in the sky. While we were there they would sometimes make statements like, "Oh, that's an Aeroflot, so it will be late for that reporting point", pointing at the fact that Aeroflot is one of the companies that 'always' aims at flying as economic as possible. To summarize this section, to efficiently perform air traffic control work, extensive procedures and agreements must exist and be supported by artifacts. Some of these artifacts, such as the telephone, allowing any kind of verbal communication, must also support coordination when the use of the procedures breaks down. And finally, and perhaps most important, none of these tools or procedures would mean anything if they were not used and applied in an intelligible manner.
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II. THE FLIGHT STRIPS AND THE CLOSED CIRCUIT TV-SYSTEM As we have seen this far in the report, there is an extensive need for coordination, which is visible both in regulations and in the supportive attitude of the controllers. The controllers work most of the time with a pen in their hands, ready to make notes of changes, not only to support their own memory, but also in order to make the changes visible to the colleagues. Pen and paper are at first glance very simple tools in the end of the twentieth century, but their main feature is the possibility for fast and spontaneous use. Two problems with handwritten notes are firstly that the notes have to be interpretable and secondly that they might be of interest to other controllers than those in the immediate area. These problems are basically solved through the use of the flight strips as the central notepad combined with a regulated notation and a closed circuit TV-system that broadcasts a recording of the current flight strips between selected groups at Copenhagen Airport. In this chapter we will focus on the use of the flight progress strips and the use of them in combination with the closed circuit television (CCTV) system. We will begin this chapter by giving a basic description of the two artifacts and there use, thereafter we will continue with describing how they are used for coordination and how they benefit from the system. The chapter ends with a discussion about paper or electronic flight strips and a conclusion.
THE FLIGHT STRIPS A flight progress strip (also referred to as 'flight strip', or 'strip' throughout this report), is a rectangular strip of paper containing printed information about a flight. Each strip is mounted in a plastic holder and placed in a column on a flight progress strip board. There is a printer in each sector, which is either handled by assistant or by the controller. Each strip contains a large amount of information, e.g. estimated time of arrival to the next way point, flight level, call sign, speed, squawk code (transponder code) etc. The exact number of possible fields are 56 (see Appendix I for more details).
Flight Identi- Speed etc Notes Time Waypoint level fication
Figure 7: The basic structure of an ACC (En Route) flight strip in Copenhagen (there are several kinds of strips, structured in different ways).
Before an airline may commence a flight they have to submit a flight plan containing information about desired route, flight level, time of departure etc. to EUROCONTROL7 in Brussels for approval. When approved, the flight plan is entered into EUROCONTROL's
7 The European organization for air traffic control.
16 Johan Berndtsson & Maria Normark, Center for Tele-Information, Technical University of Denmark File: ATC-Copenhagen.doc, Saved: 98-12-03 13:22, Printed: 98-12-03 13:24 database system, containing flight plans for all flights in Europe. All flight plans, concerning the Copenhagen FIR (Flight Information Region, the Danish airspace), are then sent to Copenhagen airport and imported into the local flight plan database. The computer system at Copenhagen Airport (it will be described more in detail in a later chapter) calculates the route the aircraft will fly and it also calculates, based on aircraft type (weight, capacity and so on) when it will be at a certain geographical point, a so called way point. There is also an arrow, showing which way the aircraft flies. Based on earlier agreements there will be a prescribed flight level in which the aircraft is to be expected. The call sign is the identification of the aircraft, and it is based on the name of the Airway Company (e.g. SAS123). Scheduled flights have the same call sign each flight. Another important identification number is the transponder code. It is the code that is entered in the transponder in the aircraft in order to make it possible for the radar to distinguish and identify the aircraft. As well as a prescribed flight level, there is also a speed specification. The controller can alter both the prescribed flight level and the speed so that they fits the situation better according to surrounding traffic. This highly compressed information is printed on the flight strip. The basic function of the strip is to provide the controllers with representations of each flight. This enables the controllers to plan their work a few minutes before the aircraft has reached the point in question. The strip is divided into several fields where the controllers can find, and are allowed to write, different pieces of information. These regulations regarding what to write where, is necessary to provide for a high degree of understanding between the controllers, so that everyone easily can tell the difference between e.g. the speed of the aircraft and it's current flight level. There are also rules regarding what to write within each field, and how to write it, the only 'free' space is the field for notes. Thirty minutes before an aircraft enters a specific sector a first flight strip, a so-called warning strip, based on the data in the flight plan database, is printed in the sector. Subsequent strips for the same flight are then printed twelve minutes before the aircraft is going to enter the sector, and also each time the flight plan in the local database is changed. When a new flight strip is printed it is simply put on top of the other in the plastic holder.
Flight strips are tangible tools As mentioned above, the strips are organized on flight strip boards. In Copenhagen this organization is based on navigation beacons and estimated time of arrival.
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Figure 8: A strip rack on ACC-East, sector B. The columns of the strip board are used to represent geographical separation within the sector, generally strips to the right are flights over the eastern part of the sector, and strips to the left over the western part. The darker (red or green) strips, visible in Figure 8, are so called designators. These containing information about navigation beacons, and aircraft closest to the specific beacon is placed in the bottom of the bay. In the figure you can see three designators in use (the rightmost bay is currently not in use), one in the left column, and two in the middle. The right column contains unused designators. The bottom designator in the middle column, CDA, represents 'Codan', one of the five inbound designators, airways used when approaching Copenhagen airport. In this case KLM1174 is closest to the inbound designator CDA, and DLH3092 is closest to the designator GES/CDA. Another reason for this way of organizing the strips is that there sometimes are several strips for each flight within the same sector. If the aircraft crosses more than one beacon, there will be one strip for each of them. This is the case with the flight OYBIL in the figure above (the third strip from the bottom of the left, and the fourth from the bottom of the middle column). Also, in the left column in Figure 8, one strip is placed above the designator. When there is something special with a flight, the controllers sometime place them in above the designators. In this case the strip is pink, which means that it's a flight strip for a military aircraft. Changes concerning the on-going flights are made visible in two ways. One way is to alter the flight plan database, which will generate a printing of a new flight strip in all the following sectors. Since there usually is no time for the quite complicated entering of new data in the database, changes are often, as we earlier mentioned, hand written directly on the strip. The old data is simply struck on the strip, and replaced with the new. Typical changes might be changes in flight level, due to surrounding traffic, changes in 'estimated time of arrival' (ETA), e.g. due to holding, in case there are too many incoming or leaving aircraft. Another way the controllers use to show that there is something special with a flight is to
18 Johan Berndtsson & Maria Normark, Center for Tele-Information, Technical University of Denmark File: ATC-Copenhagen.doc, Saved: 98-12-03 13:22, Printed: 98-12-03 13:24 slide the strip out of its normal place in the holder or to tilt the strip and the plastic holder so the strip 'disturbs' the normal pattern. There are no common rules for this kind of 'notification messages', but it is a commonly used method. It is usually mostly done for the controllers working in the sector. The flight strips keep the records, which are of great importance to the organization in case of an incident. Together with the closed circuit TV-system they enable air traffic controllers to cover different control positions to get quick information about the current situation in the other sectors, and what they might expect in the near future.
THE CLOSED CIRCUIT TV-SYSTEM The Closed Circuit TV-system consists of cameras linked with monitors, and the purpose of this system is to distribute the view of the flight strip rack between adjacent sectors, especially those that keep the responsibility of the aircraft for a short time, as Approach or Tower.
CAMERAS
MONITOR
FLIGHT STRIPS
Figure 9: Radar and Planner positions at sector B, ACC East. The cameras are shooting aircraft approaching Copenhagen from the South, the CDA inbound designator. The cameras together with two spotlights are, as you can see on the picture, placed right above the flight strip rack, were the current flight strips are placed. You can see the rack to the right of the controller’s shoulders. The reason for having two sets of cameras and spotlights here is that there on this position, sector B, are a lot of aircraft entering the approach area from the CDA entry point, and therefore a lot of strips in the rack. One camera is therefore aimed at the bottom of the rack, and the other at the top. This control position also has a TV-monitor were the controller can see strip racks from any other position, the default setting however is to watch the strips from the tower, to see what departing traffic to expect in the near future. The monochrome monitor is placed above the left radar to the right. The picture quality of the monitor is very good, so good that even the
19 Johan Berndtsson & Maria Normark, Center for Tele-Information, Technical University of Denmark File: ATC-Copenhagen.doc, Saved: 98-12-03 13:22, Printed: 98-12-03 13:24 smallest text is readable quite effortlessly. There are also a number of buttons beside the screen, which the controller uses to choose which strips of which sector s/he would like to see. What you see on the monitor is a square with the strips and nothing else (nothing outside the rack is filmed). The only time you see any movement on the monitor is thus when a controller makes notes on a strip or moves it (see Figure 10) in the strip rack. The movement from the controller's hand on the screen gives a hint to the watching controller that something is happening.
Figure 10: The CCTV-monitor (from the Approach W/N position) showing strips from the tower (aircraft departing from Copenhagen airport). Both photographs show the same monitor a few seconds apart from each other. Copenhagen can see Malmö ACC in Sweden, since one of the way points for Copenhagen is placed on the Swedish side of the border. Both Malmö ACC in Sweden and Copenhagen ACC provides the Approach in Copenhagen with information on the traffic around four of the five the inbound designators8. The Approach provides the Tower, the Apron Tower, and miscellaneous services, such as e.g. the Scandinavian Airlines (SAS) service center and Aero Cleaning, with pictures from the Final position, showing aircraft from approximately ten minutes before landing. The Tower then provides the Approach and the Danish ACC sectors with pictures showing the departures from Copenhagen. The Tower is also connected to the Apron Tower in that the Apron Tower provides a picture of which aircraft are about to roll out to the runways. As a technological system the CCTV-system is quite simple. Standard video cameras and monitors that are connected through a video network. However, when looking beyond the pure technology, the system, and the use of it, proves to be quite complex. Its video cameras and monitors practically interconnect all 'departments' working with, or in the immediate proximity of, Copenhagen Approach. The figure below shows a simplified map of the connected units. Even though all cameras can be viewed on all monitors the arrows indicate the default camera-to-monitor setting.
8 The reason for only covering four of the five inbound designators is that the system was built during the cold war while the amount of traffic back and forth to eastern Europe was still very low. However, with the fall of the Berlin wall the traffic over ALMA, which is the name of the designator, has increased considerably. There have been discussions about installing a fifth camera, but so far no decision has been made.
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Copenhagen Copenhagen Tower Apron Tower
Copenhagen Copenhagen Misc. services ACC Approach
Malmö ACC
Figure 11: A schematic figure showing the default connections established through the CCTV-system Originally, being located in different countries, buildings, rooms, or even parts of a room, made it impossible for the controllers to get that 'at a glance' information about what their colleagues were doing. Among other things this meant that a lot of coordination had to be done through the use of a telephone. The CCTV system was therefore introduced to reduce the amount of time consuming telephone calls between controllers at Copenhagen Airport. Instead of having to phone to coordinate e.g. flight levels and the order of the incoming aircraft on inbound estimates the controllers can use the CCTV-system instead.
Two simple scenarios To explain the architecture of the CCTV-system two simple scenarios will be presented; one for a departing flight DAL123, and one for an approaching flight SAS987. The connections shown in the scenarios are the ones that the controllers normally uses, the default setting so to say, even though they at any time can decide which camera view they would like presented on their respective monitors.
DAL123 departing from Copenhagen The Delta Airline aircraft with call sign DAL123 is departing from Copenhagen airport heading to Brussels, Belgium.
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APRON TOWER TOWER APPROACH EN ROUTE (ATWR) (TWR) (APP) (ACC)
SAS753 SAS753 SAS753 MSK996 MSK996 MSK996 DAL334 DAL334 DAL334 DAL762 SAS215 SAS713 SAS753 Sektor E Sektor D Sektor B MSK996 DAL334
DAL762 SAS753 SAS215 MSK996 SAS713 DAL334
Figure 12: Following a departure from Copenhagen airport through the CCTV-system. In the Apron Tower, the assistants are placing the strips in their strip rack in accordance with the filed flight plans. These strips are visible through the CCTV-system on a monitor in the tower. The departure controller in the tower has her or his own strips, which they place in their strip rack, which is visible to both the approach controllers (both Approach W/N and E/S), as well as the controllers on some sectors in Copenhagen ACC.
SAS987 approaching Copenhagen The Scandinavian Airlines (SAS) flight SAS987 is approaching Copenhagen coming from Stockholm, Sweden.
MALMÖ EN ROUTE APPROACH TOWER AIRLINE SAS SECTOR (APP) (TWR) (ACC)
DAL762 SAS987 SAS215 MSK996 SAS987 DAL334 SAS987 MSK996 DAL334
DAL762 SAS987 SAS215 MSK996 SAS987 DAL334
Figure 13: Following an approach to Copenhagen airport through the CCTV-system. Coming in from a Swedish sector in the Malmö FIR, the Swedish controller places the strip in the rack for flights entering the Copenhagen Approach area over the inbound designator SVEDA (close to Helsingborg, Sweden). The strip is thereby visible to the Approach W/N and the Final controller on their monitors in Copenhagen Approach. The Approach W/N controller directs the flight onto the downwind, hands it over to the Final controller who places the strip in a rack under a camera. By doing this, the strip now becomes visible to the tower controller handling arriving aircraft, but also to other interested parties such as the SAS personnel handling the gates.
COORDINATION THROUGH THE CCTV-SYSTEM To coordinate or harmonize the activities in air traffic control is crucial, since everybody basically works with the same sky but with different parts. Since the 'production' of air traffic
22 Johan Berndtsson & Maria Normark, Center for Tele-Information, Technical University of Denmark File: ATC-Copenhagen.doc, Saved: 98-12-03 13:22, Printed: 98-12-03 13:24 control also is a time critical activity, there is always a need for making the coordination activity as effective as possible. The controllers main task is to keep the aircraft separated and this is done through coordination with the pilots. In order to be able to focus on that, the other, although crucial, supporting tasks should be easy to manage. There is constantly work going on in order to develop better methods to support the work of the controllers. One such solution is the thirty-year old Closed Circuit Television System. The CCTV-system is designated to broadcast the information on the paper flight strips. It would be rather useless without the flight strips. On the other hand is the coordination work between sectors and departments largely dependent on handing over information in an as time effective way as possible. Thus is the work done on the flight strips sometimes meaningless if it does not reach other parts of the organization. In order to make this work an extensive set of prescribed signs and expressions have been developed. The flight strip has a strict order, each possible field (see Appendix I) has its own space. Since there are 56 possible fields in the database which can be printed on the flight strip, the information on the strip is very concentrated.
Figure 14: A flight strip used by the Approach This is a flight strip from the approach for the incoming flight SAS813, which is a Fokker 50 type medium coming in from the SVEDA way point. The 'I' hand written to the left indicates what weather information the pilot has gotten. Each time the weather report changes (each half an hour) the letter changes, so this information is used both to know that the pilot actually got the information and what information s/he got. The R means that it will be landing on the right runway, which is not standard. The notation in the middle is changes in flight level and the information hand written to the right are changes in speed. Also notice the stroke over the strip (before the 'R'). One could argue that the airport is not a part of the Civil Aviation Authority so therefore the Air Traffic Controller’s needn’t bother with the work of the Airport, however the satisfaction of the customers is just as important to CAA as to the Airport. Thus, in the new system, the possibility to keep the Airport informed of the current status, both in which order the aircraft are landing, and when they are handed to the Tower, should be included. One air traffic controller stated: "It (the CCTV-system) is very smart, you get rid of a lot of coordination, else you have to grab the phone and call each time, as they do in other places." Interview with Tower/Approach ATC Officer in Copenhagen, 1998- 06-17 There are situations where the controllers are solely dependent on the information presented through the CCTV system, e.g. the controllers in approach (West/North and East/South)
23 Johan Berndtsson & Maria Normark, Center for Tele-Information, Technical University of Denmark File: ATC-Copenhagen.doc, Saved: 98-12-03 13:22, Printed: 98-12-03 13:24 handling departures, and the controller handling arrivals in the tower. In these positions, the controllers do not receive any flight strips at all, they have to base their decisions on the strips they see on the CCTV-system. The reason for not having any strips on these positions claims to be because the aircraft are in these sectors during a very short period of time. Another reason seems to be that it is traditional, logically speaking, the aircraft are just as long in departure approach (no strips) as arrival approach (with strips). If the only source of information about incoming aircraft to the sector is through the CCTV- system, one can understand the importance of a correct and clear use of the flight strips in the system. An important issue in air traffic control seems to be the repetitive, somewhat strict behavior for smooth coordination in air traffic control. The tower is e.g. marking the strips with a letter, which is of importance for the approach: "It is a C here (pointing on the strip), it means that he has got a clearance, he has got a CHARLIE. CHARLIE is referring to the runway, which is runway 22. If it had been runway 04, he would have got an ALPHA clearance." Interview with Tower/Approach ATC Officer in Copenhagen They also put the strips in the order that the flights are coming, another important information to the approach: "They put the strips in order so we can see… were they are going and which way they are leaving… and what flight level they should have. A departure time is also written, the actual time is not so interesting, it only indicates that 'here it comes', kind of, it would be enough with a stroke. This is how one can plan were it should go, as to… make it possible to do some separation, when one now what to say to them." Interview with Tower/Approach ATC Officer in Copenhagen One function that the Flight Strip/CCTV-system serves is to inform the airport about when the flight is about to land. From the beginning the controllers in the approach control drew a stroke over a strip when they handed the aircraft over to the Tower, just for themselves as a reminder that it had been done. Then, some controllers stopped making that stroke, since they thought they didn’t need that reminder. This resulted in the airport calling the control center every time a stroke was not made, asking the controllers why they didn’t make the stroke, since they needed it to know when to prepare the arrival of each specific flight. "It's used by the airport. Copenhagen Airport says, 'they crossed the strip, so it's about to land', then they have to get all sorts of things out to the gate where where the aircraft is coming in. So if we don't draw a stroke, they call from the airport and say's 'it's not good enough, you have to make that stroke'. // Some people do it to remember that 'I have handed the aircraft over to him', but then the airport discovered this, and so… they have started to use it." (Interview with Approach Controller 980617)
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The handwritten information on the strips is the first the controllers look at, according to one of them. They are, when shown through the CCTV-system, a message from one controller to the other, which makes the latter coordinate his/hers actions in order to fit in with the incoming plane in the sector. By monitoring the flight strip rack, the controllers can also see when a change is made, because they can see the moving hand over the flight strip (see Figure 10). This is a reminder of the activities in the adjacent sector, which the controllers claim is very important. The coordination is based on agreements and rules, without which it would be impossible to coordinate the information like this. The coordination is somewhat symbolic in that the controllers do not explicitly communicate, but rather adjust their work in order to make it run smoothly.
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AFFORDANCES OF THE MEDIA
"It's very convenient since I make my notes on the strips anyway… if someone else can use them, that’s great." Interview with a Swedish ATC Officer from Malmö Airport There are several benefits from this system, some of them are already mentioned. By discussing what we have noticed as affordances in the current system, we would like to point to other needs than those that just meet the eye. The most obvious from the point of view of the controllers, seems to be the quality of saving time, or using time to what is more important. For example, there is a camera shooting a strip rack in Malmö (southern Sweden), showing the strips of flights coming in over the north east entry point (inbound way point, SVEDA) to the approach area. Before the system was implemented every hand over between Malmö and Copenhagen Approach had to be coordinated through the telephone, but with the CCTV-system the controllers in Copenhagen just look at the screen to know which aircraft are approaching, and in what order. The value of the system increased even further since a few years back when they introduced the Sequencing and Metering system, which automatically provides Malmö with timeslots, i.e. times when Copenhagen can accept an aircraft from the specific entry point. We will discuss this in a later chapter. The unobtrusive character of the system is beneficial for the controllers. Unobtrusive, since the actors themselves can choose when to check it, although not completely so since the movement of a hand or a pencil attracts attention from the controllers watching. This seems to be an issue that is of great importance to the controllers, because the uneven flow of work. When the workload is high, every obtrusive activity, not involved in the primary task to separate the flights, is a disturbance to the controllers. It is making it easier for the controllers to follow the flow of flights through the monitor and thus in the air. The order in which the strips are placed, shows the order in which the aircraft are coming. Another sign to the fellow controllers is the stroke across the flight strip, which is put there when the aircraft is handed over to the next sector. When the aircraft is handed over, the flight strip can be removed. When there is a rush hour, there is a rule that the controllers must remove the flight strips five minutes after the aircraft has been handed over. In this way, the changing, semi-persistent, content in the flight rack stipulate the work in the next sector. Drawing on the work of Schutz (Schutz, 1962; Schutz, 1964; Schutz, 1967) on actors lack of interest in the details of their colleagues work unless its affects their own work Schmidt concludes: “An actor will thus routinely expect not to be exposed to the myriad detailed activities by means of which his or her colleagues deal with the contingencies they are facing so as to ensure that their individual contributions are seamlessly articulated with the other contributions. Conversely, an actor will routinely avoid to publicize those contingent practices which colleagues do not ‘need to know’, not
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only in order to appear competent in the eyes of colleagues and managers, but also and more importantly in order to not to add to the complexity of the work of his or her colleagues.” (p. 2, (Schmidt, Forthcoming-a)) The possibility of articulating or draw attention to work that the controllers find important is an affordance in the current system. It is easy for the controllers to tamper with the strips in their plastic holders by cocking them out or make a circle or an exclamation mark by information they want to emphasize or warn about. The tower e.g. has a strip, which says "Vehicle on the runway" which they put in the flight strip rack in order to spread the information. Another example is the strip in Approach which says "Long break" in order to inform the tower that there will be slow, very few incoming aircraft, for a while. The flight strips and the closed circuit television system could be said to act as an awareness mediator in ATC-work at Copenhagen Airport. The Lancaster group has described awareness in ATC work using the term 'at a glance' observation. They have also emphasized the importance of a common notation for all people working with the strips. "Much of the work requires 'at a glance' observations of strips and flight progress boards. This can only be effective if all controllers can rapidly assimilate flight strip information and this rapid assimilation is hindered if even slight differences in strip representations are supported." (Bentley et al., 1992) Thus, there can be very few differences between what the different controllers write on the strips. The paper flight strips are tangible, movable and easy to manipulate. The handling of them does not take time; the controllers just reach for a pen and change what they want to change. Especially if the controller is assisted by an assistant, who prepares the strips and the included information as far as possible. The controllers have a good overview of the current aircraft in the sectors by looking at the strip rack. The notion of 'at a glance' is highly applicable, concerning the strips: ”Their ’at a glance’ visibility, and this is a quality we shall be emphasising, to those ’in the know’ and, perhaps more important, to those who ’need to know’ as a relevant matter for their work, such as chiefs, wingmen, shift changeovers, etc., as to what they signify about the ’state of the sector’ gives to strips their key role in air traffic management.” (p. 8, (Harper et al., 1989a)) The flight strips are, according to a statement from one of the controllers at Copenhagen Airport, also a backup system in case the radar would brake down, and used mostly for planning. The possibility to plan ahead enables the controller to foresee and solve conflicts before they arise. From the time when the first strip is printed, as early as half an hour in advance, the controller or the assistant can plan the organization of aircraft in the sector. It is
27 Johan Berndtsson & Maria Normark, Center for Tele-Information, Technical University of Denmark File: ATC-Copenhagen.doc, Saved: 98-12-03 13:22, Printed: 98-12-03 13:24 also possible for the controller to call the aircraft's current sector and negotiate about the option of changing e.g. flight level if the pre-planned level causes conflicts with other flights. Since timesaving seems to be the main reason for replacing a telephone call (or telephone coordination) with more unobtrusive solutions as the CCTV-system, we think that the affordances described in this section, match the criteria very well. Nor is the handling of the physical strips in our opinion very time consuming. Instead the tangible strips seem to solve the primary problem in a good and effective way. As we see it, there is a need for a new system that further solves and fulfils the problems of the old system, rather than replacing an analog system with a digital.
PAPERBASED OR ELECTRONIC FLIGHT STRIPS? If the CCTV-system solves the problem of time-consuming telephone calls, the computerized flight strip system solves the problem of recording the data. Today, every single flight strip has to be saved for a certain amount of days in order to be able to recover occurrences in case it is needed. The computerized system will mean something of a paradigm shift in air traffic control work, and is a often discussed topic of research. Among others, a group at Lancaster University has presented several reports and papers on their studies, in which the Flight Strips are presented as being of central importance in air traffic control work (Hughes et al., 1988; Harper et al., 1989a)9. In their study, where they discuss why and how the controllers use flight strips, they point out that the physical properties (as their tangibility and the possibility to write directly on them) of the strips also play a major part in air traffic control work. "For, in terms of the kind of features we have identified as involved in 'working the strips' and the place they occupy in the social organisation of controlling work, many of these are related to, if not precisely dependent upon, the physical character of the strips themselves." (p. 21 (Harper et al., 1989a)) Making notes and writing signs on strips, 'cocking' them out to make point out a possible conflict, showing them to each other etc. are all of them actions that are supported by physical strips (p. 29-31, (Harper et al., 1989a)). Hopkin, who in several papers has pointed out the flexible character of paper flight strips, also supports these findings (Hopkin, 1991; Hopkin, 1995). Hopkin summarizes the use of flight strips in air traffic control in his 1995 book: "The paper flight progress strips exemplifies some of the attributes of air traffic control itself. It is incomprehensible to the layman for it contains no obvious information about what it is for, or how it is used. Initial impressions of it can be deceptively simple. It does not look complex, but seems to contain quite a small amount of information, all of which could be quantified and presented
9 See also (Harper et al., 1989b; Bentley et al., 1992; Hughes et al., 1992; Sommerville et al., 1992; Harper and Hughes, 1993; Hughes et al., 1993; Harper et al., 1994; Hughes et al., 1994; Shapiro et al., 1994; Sommerville et al., 1994)
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electronically. In fact, the paper flight progress strips has evolved into a complex and subtle tool." (p. 25, (Hopkin, 1995)) But while Hopkin's conclusions are very similar to those of the Lancaster group, there are other researchers who have come to very different conclusions. A group at the University of Oklahoma, USA, have been doing extensive research on among other things the use of paper flight strips and in several papers claimed that they in fact are not very useful at all. In a paper from 1995 they state that the controllers "feel that the only tool necessary for air traffic control is the radar, and that any time spent away from the radar is time spent away from their primary task" (p. 2 (Edwards et al., 1995)), and in another paper that: "The pattern of findings implies that board management was affected by the complexity of the of the scenario. In the more complex scenarios, the controller was forced to find time to keep the board configured and updated, and he or she did this in concentrated time segments. During these times, controllers may feel that they have 'been taken away' from the plan-view display and the traffic situation." (pp. 341-342, (Vortac et al., 1993)) Their conclusions are obviously almost contradictory to what has been presented by the Lancaster group and by Hopkin. To conclude this brief comparison between the results of the studies from Hopkin, the Lancaster, and the Oklahoma group, it has to be said that the studies were made using very different methods. The Lancaster group used a sociological approach and ethnographic field studies to collect data, while both Hopkin and the Oklahoma group draws upon the tradition of Human Factors, and to a large extent rely on structured interviewing and surveys. Another, and perhaps more important difference, is that both the Lancaster group and Hopkin have been studying ATC work in the UK, while the Oklahoma group have performed their studies in the US. It may thus be that the strips have a greater importance in work arrangements similar to those in the UK, than in those in the US. An interesting aspect in this discussion about the existence or non-existence of paper flight strips, is that we have found references supporting the Oklahoma group's claims regarding the opinions of the controllers, both in discussions with controllers at Copenhagen airport, and in the attitude of parts of the air traffic control industry. In a substantial number of our interviews, when asking the controllers which their most important tool is, they replied that the radar is the most important one. Also, several air traffic controllers have in interviews stated that the current way of working with paper flight strips takes too much effort and time: "In some sectors we have up to three strips for the same flight, and there simply isn't enough time to handle them all " Controller from Copenhagen ACC West, Interviewed 980714 in EUROCONTROL's test center in Bretigny, France Today the air traffic control organizations are looking into the possibilities of the computer and to develop a 'strip-less' computerized system. According to EUROCONTROL, this issue has been addressed for a long time, and there does not seem to be any alternatives with strips.
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An aspect which has to be remembered is that the flight progress strips actually are outputs from a computerized system - the flight plan database. And the reason for having them printed is that the technology wasn't good enough to enable the controllers to handle the flight strip information in a satisfactory manner, behind a screen, when the database handling of flight strips first was implemented. In a way the attempts to find strip less ways of controlling may therefore be regarded as a test, to see if the technology is ready to provide the controllers with the support they need, without 'resorting' to using paper. Both the Lancaster group and Hopkin conclude that, "the paper flight strips has evolved into a complex and subtle tool" (p. 25, (Hopkin, 1995)), and with this we fully agree. The paper flight strips are not in any way irreplaceable as a tool for the air traffic controllers, but they do fulfill several essential functions that have to be fulfilled regardless of what the system might look like in the future. As pointed out by Hopkin, the failure of early "attempts to replace paper flight strips with electronic ones emphasized their attributes instead of their functions". Furthermore, "the strips contain no functional information about their purposes, their uses, or the meaning of their contents" (p. 62, (Hopkin, 1991)). Thus, just copying the attributes would not provide solutions to the many functions that the paper flight strips fulfil. "In conclusion, whatever form electronic flight strips take, it is essential to define beforehand all the functions of paper flight strips, in order to discard any unneeded functions deliberately and inadvertently, to confirm that familiar essential functions can still be fulfilled electronically, and to appreciate the functional and cognitive complexity of paper flight strips." (p. 64, (Hopkin, 1991)) While we do agree with the essence of Hopkin's statement, we also believe that there has to be enough 'room' to solve unforeseen problems outside of the system, when they occur - because they will. It is impossible to foresee all possible situation in any complex work domain such as that of air traffic control. This also introduces the question of how to find these coordinative functions that the strips, and in the Copenhagen case, the CCTV-system, fulfill.
CONCLUSION There are several benefits and problems in the current system that we have picked up and we are finishing this chapter trying to sketch the current situation. The problems first: The system is old, and there are problems with the traffic load. The database cannot store more than a certain flight plans at once and when it is full, the rest will not be in it, and all the consequences that might result in… Another problem is the workload in relation with the amount of controllers. If you split up the sectors (and thus split the workload), there will be a large numbers of hand overs, which are a time consuming activity as well as a source of possible errors. Splitting the sector is thus not an option. One consequence of the workload is that the controllers don't have time to update the database with new information, since they have to feed the information into the computer by hand, and thus is the database inconsistent and not up to date. A consistent database is very useful to the organization as such, since all data has to be saved in case of an accident.
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It is likely that the system as such could be successfully replaced, but, as we have tried to point out, the system serves several purposes, not all of which were originally intended, that need to be taken into consideration in the design of the new system. It is the use of the artifacts that is the important aspect. What do we learn from the study of the flight strips and the closed circuit TV system? One of the most important aspects of the air traffic control work is that everything has to be externalized, recorded and saved in case of an accident or, more often occurring, to enable the overtaking by another controller. No information can be ‘kept in the head’ until there is more time to print it down. From what we have seen and heard from the controllers, the most important aspect in developing strategies for the work, seems to be to reduce any costs of time. This means that every recording of actions has to be able to execute very quickly. There seems to be a need to be able to alter the artifact (in this case the flight strip) in an almost casual way, a quick note or a quick tilt, just as a remainder. The hand moving and altering the strip is obvious enough to be noted on the screen, although the controller is focusing on something else. The CCTV-screen seems to be large and with a suitable brilliance or contrast to easily give the controller to note the information almost by glancing. The flight strips are not in themselves irreplaceable as tools in Air Traffic Control. The important thing is to understand exactly what they do in ATC-work before trying to replace them. In a discussion with a controller from Malmö, Sweden about the flight strips and the CCTV-system, she said that she thought that they would do fine without strips, but that they could never remove the CCTV-system. Of course the CCTV-system would be useless without the strips, but the point that she was trying to make was that the system, the way it works today, fulfils a function that has to be kept intact. It is not the actual artifact, but merely what it does and how it works that is important. We hope that it is a point taken by the developers of the new systems.
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III. FUTURE WORK At the moment we are continuing our field studies and writing on this report simultaneously. For us there are three other coordinative artifacts, aside from the Flight Strips and the CCTV- system that we are currently looking at – the database system for flight plans, the electronic hand over system, and the Sequencing and Metering system.
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REFERENCES Bentley, R., J. A. Hughes, D. Randall, T. Rodden, P. Sawyer, D. Shapiro, and I. Sommerville (1992): Ethnographically-informed systems design for air traffic control. In J. Turner and R. Kraut (eds.): CSCW ’92. Proceedings of the Conference on Computer-Supported Cooperative Work, Toronto, Canada, 31 October—4 November, 1992. New York: ACM Press, pp. 123-129. Edwards, M. B., D. K. Fuller, and O. U. Vortac (1995): The Role of Flight Progress Strips in En Route Air Traffic Control: A time-series analysis. International Journal of Human-Computer Studies, vol. 43, no. 11995, pp. 1-13. Eurocontrol (1998): http://www.eurocontrol.be/. . Halverson, C. (1994a): Distributed Cognition as a Theoretical Framework for HCI: Don't Throw the Baby Out With the Bathwater - The Importance of the Cursor in Air Traffic Control. Department of Cognitive Science, University of California, 1994a. Halverson, C. (1994b): Traffic Management in Air Control: Collaborative Management in Real Time. SIGOIS Bulletin, vol. 15, no. 21994b, pp. 7-10. Halverson, Christine A. (1995): Inside the Cognitive Workplace: New Technology and Air Traffic Control. Ph. D., University of California, San Diego, San Diego, 1995. Halverson, C. A., K. Harwood, T. J. Davis, and C. R. Brinton (1992): A systems approach to design: Developing a usable automation tool for air traffic control. Proceedings of the Eleventh Digital Avionics System Conference, Seattle, WA. IEEE, pp. 167-173. Harper, Richard, John A. Hughes, Dan Shapiro, and Wes Sharrock (1994): Ordering the Skies: The Sociology of Coordination Work. London: Routledge. - [Forthcoming]. Harper, Richard H. R. and John A. Hughes (1993): What a f—ing system! Send ’em all to the same place and then expect us to stop ’em hitting. Managing technology work in air traffic control. In G. Button (ed.): Technology in Working Order. Studies of work, interaction, and technology. London and New York: Routledge, pp. 127-144. Harper, Richard R., John A. Hughes, and Dan Z. Shapiro (1989a): The Functionality of Flight Strips in ATC Work. The report for the Civil Aviation Authority. Lancaster Sociotechnics Group, Department of Sociology, Lancaster University, January, 1989a. Harper, R. R., J. A. Hughes, and D. Z. Shapiro (1989b): Working in harmony: An examination of computer technology in air traffic control. EC-CSCW ’89. Proceedings of the First European Conference on Computer Supported Cooperative Work, Gatwick, London, 13-15 September, 1989, pp. 73-86. Hopkin, D. (1991): Automated Flight Strip Usage: Lessons from the functions of paper strips. Proceedings on AIAA/NASA/FAA/HFS symposium on challenges in aviation human factors: the national plan, pp. 62-64. Hopkin, D. (1995): Human Factors in Air Traffic Control. London, UK: Taylor & Francis Ltd. Hughes, J. A., V. King, T. Rodden, and H. Andersen (1994): Moving Out from the Control Room: Ethnography in System Design. In R. Furuta and C. Neuwirth (eds.): Proceedings on the Conference on Computer Supported Cooperative Work, CSCW'94. ACM Press.
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Hughes, J. A., D. Randall, and D. Shapiro (1992): Faltering from ethnography to design. In J. Turner and R. Kraut (eds.): CSCW ’92. Proceedings of the Conference on Computer-Supported Cooperative Work, Toronto, Canada, 31 October—4 November, 1992. New York: ACM Press, pp. 115-122. Hughes, J. A., D. Randall, and D. Shapiro (1993): From ethnographic record to system design: Some experiences from the field. Computer Supported Cooperative Work (CSCW). An International Journal, vol. 1, no. 31993, pp. 123-141. Hughes, John A., Dan Z. Shapiro, Wes W. Sharrock, and Robert Anderson (1988): The Automation of Air Traffic Control. Lancaster Sociotechnics Group, Department of Sociology, Lancaster University, October, 1988. Schmidt, K. (Forthcoming-a): The critical role of workplace studies in CSCW. In C. Heath, J. Hindmarsh, and P. Luff (eds.): Workplace Studies: Recovering Work Practice and Informing Deign. Schmidt, K. (Forthcoming-b): The Discipline of Steel: Coordinating distributed activities in time-critical production.Forthcoming-b. Schutz, Alfred (1962): Commonsense and scientific interpretations of human action. (1962). In A. Schutz: Collected Papers, vol. 1. The Hague: Martinus Nijhoff, 1962, pp. 3-47. Schutz, Alfred (1964): The problem of rationality in the social world. (1964). In A. Schutz: Collected Papers, vol. 2. The Hague: Martinus Nijhoff, 1962, pp. 64-90. Schutz, Alfred (1967): The Phenomenology of the Social World. Translated by G. Walsh and F. Lehnert. Evanston, Ill.: Northwestern University Press (Originally published 1932). Shapiro, Dan Z., John A. Hughes, David Randall, and Richard Harper (1994): Visual re- representation of database information: The flight strip in air traffic control. In M. J. Tauber, D. Mahling, and F. Arefi (eds.): Cognitive Aspects of Visual Languages and Visual Interfaces. Amsterdam: Elsevier. - [Forthcoming]. Sommerville, I., R. Bentley, T. Rodden, and P. Sawyer (1994): Cooperative Systems Design. The Computer Journal, vol. 37, no. 51994, pp. 357-366. Sommerville, Ian, Tom Rodden, Richard Bentley, and Pete Sawyer (1992): Sociologists can be surprisingly useful in interactive systems design. In A. Monk, D. Diaper, and M. Harrison (eds.): Proceedings of HCI’92, York University, September 1992, vol. VII, pp. 341-354. Vortac, O. U., M. B. Edwards, and J. P. Jones (1993): En Route Air Traffic Controllers' Use of Flight Progress Strips: A Graph-Theoretic Analysis. The International Journal of Aviation Psychology, vol. 3, no. 41993, pp. 327-343.
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APPENDIX I: FIELDS ON THE FLIGHT STRIP A strip format is made of several fields that are automatically extracted from the flight plan for the strip printing. These fields are:
1. ADEP departure airport 2. ADES destination airport 3. AH actual time departure (hour) 4. AM actual time departure (minutes) 5. ASTERISK asterisk 6. ATD actual time departure 7. CLS aircraft call sign 8. CN arrow before NFL 9. CS arrow before SFL or SFLX 10. CX arrow before XFL (exit flight level) 11. DESIG designator 12. DIR arrow calculated from DIRFROM 13. DIRFRO direction from 14. DIRNEXTdirection next 15. EET estimated elapsed time 16. EH estimated off block time (hour) 17. EM estimated off block time (minutes) 18. ENDU endurance 19. EOBT estimated off block time 20. ETO estimated time of overflow on designator 21. ETO1 estimated time of overflow of reference point 1 22. ETO2 estimated time of overflow of reference point 2 23. INTERN international flight 24. NAV navigation field 25. NB number of aircraft 26. NEXT next reporting point 27. NCROS entry crossing level 28. NFL entry flight level
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29. OH estimated time of overflow on designator (hour) 30. OM estimated time of overflow on designator (minutes) 31. PEND pend indicator 32. PREVI previous reporting point 33. REF1 reference point 1 34. REF2 reference point 2 35. REMARKS remarks 36. REPL replacement sign 37. RFL requested flight level 38. ROAD1 char 1 - 5 of the route from the SPC sheet 39. ROAD2 char 6 - 10 of the route from the SPC sheet 40. ROAD3 char 11 - 15 of the route from the SPC sheet 41. ROU1 char 1 - 4 of the route from the SPC sheet 42. ROU2 char 6 - 9 of the route from the SPC sheet 43. ROU3 char 11 - 14 of the route from the SPC sheet 44. ROUTE route from the SPC sheet 45. RWY runway 46. SFL standard flight level 47. SID standard instrumental departure 48. SSRA SSR code A 49. SSRB SSR code B 50. TAS true air speed 51. TRANSIT transit sign 52. TYPE_W type and WTC of aircraft 53. WARNING warning strip indication 54. XCROS exit crossing level 55. XFL exit flight level 56. XSFL exit flight level or standard level
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