AAWSAP DIRD, Cognitive Limits on Simultaneous Control of Multiple Unmanned Spacecraft, December 2010

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Chapter 3: Studies in Cognitive Workload for Air Traffic
Controllers
There are a few areas of research applicable as analogues to the piloting of several
aircraft. The largest of these areas analyzes the supervisory functions of air traffic
controllers (ATC). In a typical ATC duty environment, a single operator is responsible
for many fully-autonomous aircraft. ATC is either airport-based or en-route. Airport­
based facilities include ground control, local control for active runways (Tower control),
and approach control, which in the US is called Terminal Radar Approach Control, or
TRACON. A zone of air-controlled space assigned to a specific control center is that
center's sector; similarly, a given controller is responsible for a sector of airspace.
Between airport-controlled sectors, aircraft are monitored by an en-route facility.
TRACON is the most cognitively demanding function in this chain. Terminal controllers,
as ATCs are called at TRACON facilities, are responsible for departures after take-off,
and approaches and flyovers within about a SO-mile radius of the airport.9 Approaching
aircraft need to be vectored by the controller into an appropriate flight path for landing,
avoiding all other aircraft in the air or soon to be in the air, and then handed off to the
Tower controller for landing and ground instruction. Departing flights and flyover traffic
mainly need to be monitored for conflicts. Approaching aircraft are by far the most
cognitively challenging in the ATC task. Images of air traffic controller environment and
displays are shown in Figure 3.h
Errors in flight control are called anomalies in the industry. The most common aircraft
anomaly is deviation from flightpath in en-route sectors. This anomaly is corrected by
pilots themselves or after instruction from the appropriate ATC. The most common ATC
error is miscommunication between controllers in an aircraft handoff between sectors. 19
A study in 1997 by the National Academies showed that ATC errors occurred in both
high and low workload conditions, as predicted by overload and disengagement. 20
In looking at the cognitive limits in ATC, we should seek where typical controllers enter
the B region of workload. Traffic load defined as simply the number of aircraft does not
by itself show the complete picture of ATC workload. In a study of professional
controllers in 2006, Boag recorded subjective measures of workload and reaction time
when static air traffic displays were presented. Displays included air traffic conflicts of
differing complexity that required resolution. Complexity in the display was objectively
ranked using the Method of Analysis of Relational Complexity (MARC). 21 Results showed
that a relatively small number of aircraft can greatly increase the perceived workload.
Boag concludes that perceived complexity is the number one factor in determining
workload, and that although conflicts are the major source of complexity in the ATC
task, and these can be modeled somewhat using a combination of aircraft separation
and transition1 variables, individual differences still have significant impact on when a
controller may reach overload. 22
9 Each facility will vary in TRACON sector radius. For smaller airports, TRACON functions may be performed by a
nearby en-route facility.
h Of historical note in the US Air traffic Control industry was the industry-wide strike begun on August 3, 1981, by
the nearly 13,000 ATC specialists. Only 1300 obeyed a Presidential order to return to work under the "peril to
national safety" provision of the 1947 Taft-Hartley Act. On August 5, 1981 the remaining 11,345 controllers were
fired and banned for life from federal service. The FAA rebuilt the force to pre-strike levels during the rest of the
1980s. This event resulted in a dearth of research during the 1980s on air traffic control professionals.
1 An aircraft transition is an event such as landing, hand-off to another controller, or entering/leaving a sector,
where a sector is defined as a controller's airspace of responsibility.
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