Air Traffic and Navigation Services SOC Limited (ATNS) provides air traffic, navigation, training and associated services within South Africa and a large part of the Southern Indian and Atlantic Ocean, comprising approximately 10% of the world's airspace.

The 20th October was International day of the Air Traffic Controller; hopefully the pilots out there wished their ATC’s a good day.

The air traffic controller plays a central role in the safety of the air traffic system. Amongst other responsibilities, the controller reduces the pilot’s workload by taking over the role of detecting and resolving conflicts with other aircraft operating in the same or adjacent airspace, and by providing warnings and advice of known weather hazards and possible military airspace infringements. But in order to understand how miscommunications can occur between pilots and controllers, it is necessary to understand the differing perspectives they each have of the system.

The goal of the air traffic system is to accomplish “the safe, efficient conduct of aircraft flights” and “to maintain a safe, orderly and expeditious flow of air traffic” Air traffic controllers, with their common language, are the crucial link in international aviation. The seamless flight of air traffic across international borders and through jealously guarded sovereign airspace of, often, mutually antagonistic nations would not be possible without the co-ordination of controllers. Whether internationally or nationally, the joint goals of safety and efficiency are accomplished through an intricate series of procedures, judgments, plans, decisions, communications and co-ordinating activities. The public is familiar with the radio communications which occur between pilots and controllers but equally as critical are the co-ordinations within and between air traffic control facilities when controllers “hand-off” aircraft as they pass from one controller’s sector of responsibility to another. “The predominate factor of the ATC system”, is that it is centred on the controller with all the safety critical decisions emanating from that source”.

Air traffic control developed from its initial role of communicator and traffic advisor to separation estimator and flight path decision-maker. With the coming of radar, decision-making and judgement functions of ATC increased to the extent that today it has also taken on the role of traffic flow director. The nature of the job and the problems encountered differ with the services being provided by controllers at various control positions namely, Tower controllers, Area controllers, Radar controllers and Approach controllers.

Such job descriptions fail to convey the complexity of the four-dimensional (space and time) conundrum, air traffic control is complex, more so than it seems at first to an uninformed observer. Most of air traffic control is not inherently meaningful, and it has only become meaningful to the controller because of training. The controller’s job is a strange and specialised one—on one hand the controllers are expected to apply strictly defined procedures and abide by countless regulations, yet at the same time, they are confronted with new situations requiring substantial flexibility in their response.

The three-dimensional nature of aircraft trajectories can only be displayed on a two-dimensional radar screen or, more awkwardly, on a two-dimensional procedural display console. The controller must think in three-dimensions and predict a fourth.

Mastering the three-dimensional movement is further complicated by the speed at which it occurs. This reduces the time to recognise, evaluate and react to unexpected problems. It is a matter of reaching quick, workable decisions and not of looking for a perfect solution but finding it too late. Often heuristic thinking is required, not algorithmic.

There is little leeway for correction. Safety tolerances are usually large but the rapid sequence of events reduces the time remaining to register or correct errors. Controllers must be able to concentrate and react rapidly.

Minor errors or slips can cause serious accidents yet these are difficult to detect. Human error has been called “the relentless threat to aviation safety” (Maurino, Reason, Johnston and Lee, 1995).

The aviation system is in the vanguard of technical development. ATC procedures are in a state of virtually constant change which must be assimilated. Constant retraining, changes to procedures, equipment and aircraft types and performance characteristics require controllers to constantly adapt and be mentally flexible or be overtaken by change.

Although trained to deal with many potentialities, pilots in their normal work ideally should encounter no problems. But the routine work of a controller almost exclusively exists of problem solving, in trying to accommodate traffic safely, efficiently and in an orderly manner in the available airspace. Pilots and controllers have differing perspectives of the conflicting pressures of safety and efficiency. Firstly, a controller has several aircraft to deal with whereas a pilot is concerned with one. The pilot wants to fly the aircraft in the most efficient manner by choosing direct routes or those with the most favourable winds and optimal altitudes. This is not always compatible with the controller’s problem of safely managing numerous climbing, descending and crossing aircraft spread throughout a large airspace volume but converging and congregating at a few airports or navigation aids.

Secondly, the controller’s perspective of efficiency differs because his or her goal is to maintain an evenly spaced flow of all aircraft from airport to airport, even if this means slowing, holding or ‘track stretching’ aircraft to delay their arrival. The aircraft crew are under pressure to deliver their passengers on time and to ensure that the aircraft is available for its next scheduled flight. The controller tries to maintain sensitivity to the crew’s need to avoid excessive and abrupt manoeuvring (for passenger comfort) while achieving safe separation with other aircraft and efficient sequencing.

There are numerous causes for tension, such as the role of the controller as “traffic cop”, the propensity for pilots to bend the truth on time estimates and weather conditions to gain a higher priority and track shortening, and due to perceived status and salary differences. The relationship is unique, because it is not based on emotional attachments nor on political commitments nor organisational pressures. The pilots’ convictions of positive expectations are based upon repeated successes of consistent, successful and dependable performance. On any flight, a pilot deals with a dozen or more controllers, none of whom are known personally, and, similarly, a controller deals with dozens of pilots. In order for the system to work, exchanges must be calm and professional. Controllers supply the support that has enabled all skill levels of pilots flying all types of aircraft to safely complete all types of flight plans through airspace and to airports of all complexity levels in all types of weather. Pilots, because they have an incomplete knowledge of the air traffic situation, literally put their own lives and the lives of their passengers in the hands of controllers. They place a heavy reliance on the voices of the air traffic control system.

The pilot’s task then, except in an emergency, is to receive advisory information, accept instructions, and to act upon them. The pilot must trust a controller’s commands because he or she is not, in general, in receipt of enough information regarding the traffic disposition to question them. The pilot provides an element of redundancy by reading back certain instructions, such as clearances, but otherwise provides little information unless first asked for it. But speech between controllers and pilots also fulfils several functions more related to the disciplines of social and personality psychology. As we shall see later, pilots and controllers make judgements about each other based on what is said and how it is spoken.

The teamwork reflected in communication between pilots and controllers is a critical component of the air traffic system because it provides the system’s flexibility. Most controllers are not pilots and most pilots are not controllers. Instead of just having impersonal radio contact, it has proved worthwhile for pilots and controllers to observe each other at work. The more they learn about each other, the easier it is to recognise and discuss common interests. Many problems of communications stem from the lack of knowledge the parties have about each other.

Situational awareness may be defined as “the perception of the elements in the environment within a volume of time and space, the comprehension of their meaning, and the projection of their status in the near future”. This obviously differs for pilots and controllers. Situational awareness for pilots refers more to the operation of the aircraft and controlling its flight path trajectory. But because they are required to maintain a ‘listening watch’ on the control frequency, pilots can build up a less-than-perfect idea of the activity occurring in the airspace sector depending upon factors such as traffic density, airspace size, their time on the frequency and their own workload. However, they often lack enough information with which to evaluate and question controller instructions, even if the instructions are wrong (unless they are obviously incorrect). It has been suggested that this places a heavy burden on the controller, who in this respect is unprotected by the redundancy so carefully designed into most aspects of the aviation system. But in some circumstances the pilots’ listening watch can detect controller errors. This was graphically illustrated by the potential mid-air collision near Mount Isa in 1991 which was averted by the situational awareness of one of the aircraft crews.

A controller taking over a sector from another will need to build a mental picture of the air traffic before accepting responsibility for the position. Controllers refer to situational awareness in terms of having (or losing) ‘the picture’ which includes knowledge of the past, present and future situation of not only the aircraft disposition, but also weather forecasts, military airspace status, runway and navigation aid availability, adjacent sectors, degraded modes of equipment, staffing, changes to traffic handling rules and procedures, and so on. The controller’s picture consists of all that is perceived and is meaningful, interpreted in the context of recalled events preceding the current situation, anticipated events predicted from the current situation, and professional knowledge and experience used to maintain control over the air traffic through sanctioned rules, practices, procedures and instructions.

Many ATC positions are staffed by two controllers, especially during peak traffic periods. They work together with one controller handling radar monitoring and communications and the other dealing with flight plan data and co-ordination. Thus a team manages the aircraft of the sector but a single controller usually communicates with the air traffic. This not only divides the task load but, to the extent that tasks overlap, it also provides redundancy in the form of additional eyes and ears to maintain situational awareness.

A significant number of speech transmissions by controllers are directed at maintaining situational awareness. It was one of a number of strategies used to monitor the workload and actively update the working memory. The process of issuing instructions and updating the flight strips (upon which are encoded the relevant details of, and subsequent instructions to, each flight), assists the controller in maintaining the picture. However, high levels of communications may not only increase controller workload but may also impact negatively on the controller’s ability to maintain situational awareness. When controllers spend more than half their time communicating with pilots, they report that their traffic awareness becomes disturbed. When this occurs, the effect of any normally small impact task may affect mental work load and performance. Controllers may use their communications in an attempt to control their workload; slowing down their rate of speech and not condensing their messages may provide them some residual control over their workload, allowing time to keep their flight strips up-to-date and to plan.

Controllers and team leaders may infer another’s planned course of action by overhearing communications directed to others. This pattern of indirect communications and inference is contingent upon controllers developing a “shared mental model” and allows teams to co-ordinate their behaviour even when task load makes personal communications impossible. As a flight passes from one sector to another, the controller may need to pass on aspects of his or her situational awareness to the next controller. Prior to Avianca Flight 052’s crash near New York in 1990 which killed 73 people, important information about the aircraft’s fuel status was passed by the crew to controllers in one facility but this information was lost at the point of hand-off to another. The approach controllers then treated the flight like any other when they could have expedited the aircraft’s approach.

A mismatch of situational awareness between controllers and aircraft crews is a source of miscommunication. An example is the breakdown of separation between two Boeing 737’s in the Cullerin holding pattern (near Sydney) in 1994 where, following control instructions, pilot and controller expectations of aircraft actions differed, exposing a critical gap in procedures and a subsequent refinement of ATC phraseologies. Another is the 1972 crash of Eastern Airlines Lockheed Tristar into the Everglades near Miami which killed 103 people. The controller, watching the aircraft slowly descending, knew that the crew was engaged in determining the status of their nose landing gear, but like the crew, he did not know that the auto pilot had been inadvertently disengaged. He simply asked, “How are things coming along out there?” an insufficiently precise question to bring the crew out of their mental state. They remained preoccupied with the nose gear indicator and the aircraft descended into the swamp.

The successful and safe outcome of the “Alliance” is fully dependent on trust and mutual respect from both parties involved.