“Don’t
talk to him too much”, the captain advised the first officer of the air
traffic controller. “He’s trying to get us to admit we made a big mistake
coming through here”.
—cockpit
voice recorder transcript,
Lockheed 188A Electra crash near Dawson, Texas, 1968.
(Gero, 1996)
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 Air Traffic Control 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 nationally or internationally, 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, Terminal area controllers, Enroute controllers,
Flow controllers, and Flight service officers.
Such job
descriptions fail to convey the complexity of the four-dimensional (space
and time) conundrum. Hopkin (1995:153) writes that “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”. Muller (1996)
describes the controller’s job as 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.
There are
several distinguishing features to air traffic control:
-
Three-dimensional nature of movement: 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.
-
Speed and
stress: 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.
-
Limited
correction possibilities: 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.
-
Great
significance of small errors: 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).
-
Constant
changes: 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.
The “Awkward Alliance”
Ruitenberg
(1995) has contrasted the work of pilots and controllers. 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
maneuvering (for passenger comfort) while achieving safe separation with
other aircraft and efficient sequencing.
Besco (1997)
has labeled the controller/pilot relationship the “awkward alliance”.
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, he states, 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 role of the
pilot in the exchange of verbal information differs from that of the
controller and is succinctly established in the Air services Australia
Civil Aviation Regulation (CAR) 100:
(1) An aircraft
shall comply with air traffic control instructions.
(2) The pilot
in command of an aircraft is responsible for compliance with air traffic
control clearances and air traffic control instructions. (Civil Aviation
Safety Authority, 1998)
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. 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.
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
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 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 (Hopkin, 1995).
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 (Bowers, Blickensderfer and
Morgan, 1998). 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 terminal
area controllers then treated the flight like any other when they could
have expedited the aircraft’s approach (Roske-Hofstrand and Murphy, 1998).
A mismatch of
situational awareness between controllers and aircraft crews is a source
of miscommunication. An example is the break down 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 (BASI, 1997b), 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 comin’ 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 (Gero,
1996).