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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. The closure of many
regional control towers, flight service units and briefing offices during the past two
decades has markedly reduced the face-to-face contact between pilots and air traffic
service personnel.
2.3 Situational Awareness
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” (Endsley, 1995). 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). Billings and Cheaney (1981:90) suggest 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 (see appendix 1).
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. Hopkin (1995:58) writes that
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
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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.
Redding (1992) discovered that 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 (Endsley and Smolensky, 1998).
Jorna (1991, cited by National Research Council, 1997) found that 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
　
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