FLIGHT ALLOCATION IN SHARED HUMAN-AUTOMATION
EN-ROUTE AIR TRAFFIC CONTROL
G. de Rooĳ, C. Borst, M.M. van Paassen, M. Mulder
Delft University of Technology
Delft, the Netherlands
Allocation is a challenge for higher levels of automation in air traﬃc control,
where ﬂights can be dynamically assigned to either a human or an automated
agent. Through an exploratory experiment with six professional air traﬃc
controllers, insight was gained into the possibilities and challenges of human-
automation teamwork in an en-route environment. Participants showed high levels
of automation trust, but mostly ignored automation-suggested allocations,
preferring a highly automated sector instead. Most ﬂights were delegated to
automation, after they were given a direct and conﬂict-free path. Flights handled
manually were those requiring level changes or non-standard routing. Future
research should focus on establishing speciﬁcally which ﬂights can be automated.
Air traﬃc controllers (ATCOs) work in a challenging and demanding environment. The
continuous quest for more eﬃcient and safer air travel, drives the development of more advanced
automation. Both Europe and the United States aim for higher levels of automation in the com-
ing decades with a more supervisory/strategic role for humans (Prevot, Homola, Martin, Mercer,
and Cabrall (2012); SESAR Joint Undertaking (2019)). In such an environment, less people can
handle more traﬃc in larger sectors. Despite high levels of automation, humans are expected to
play an important role in supervising these future systems and to intervene when automation falls
short (Metzger and Parasuraman (2005)); people will ultimately remain responsible.
To be able to intervene, it is essential that ATCOs maintain vigilance, situation awareness
and a suﬃcient skill level to perform tasks manually (Bainbridge (1983)). This could be achieved
by not making the human a supervising bystander, but have him/her work side-by-side with au-
tomation in a team, both able to perform and share tasks. This sparks the question of what such
co-operation should look like, and what impact it will have on human-automation performance.
Currently, airspace is divided into sectors, each under the responsibility of a diﬀerent
ATCO. This requires considerable coordination between adjacent sectors and may lead to an
imbalance in traﬃc load (and thus workload). To mitigate these issues, Birkmeier, Tittel, and
Korn (2016), among others, considered so-called ﬂight centric or sectorless operations. Instead of
coupling controllers to geographic areas, a single controller would be assigned to several ﬂights,
from departure to arrival, reducing the number of handoﬀs and possibly providing a better work-
load balance. This, however, also introduces new challenges. Consider, for example, when two
ﬂights under control by diﬀerent ATCOs are in conﬂict. Who should then solve the conﬂict?
What if that other controller is not another human, but an automated system? How are
ﬂights then assigned to either a controller or automation? Should all aircraft involved in a conﬂict
be controlled by either the ATCO or the automation, so as to mitigate additional workload related
to coordination? If not, who solves a conﬂict? In addition, with an automated agent, it becomes
possible to share (sub)tasks dynamically, back and forth, between human and automation. This
could establish true teamwork, but only if above-mentioned questions have been answered ﬁrst.
This paper discusses an exploratory experiment on the allocation of ﬂights in a shared
human-automation en-route airspace. Control over which ﬂights were automated was given to the
ATCOs themselves, although initial automation-based suggestions were given for each ﬂight.
Participants and Apparatus
Six professional ATCOs (age M = 38.3, SD = 10.0, years of experience M = 14.8,
SD = 8.7), from Maastricht Upper Area Control (MUAC) participated in a real-time simulator
experiment. A TU Delft-built Java-based simulator (Fig. 1) was designed to mimic the MUAC
interface, to ensure that participants could focus on working with the experimental automation.
A 1920 x 1920 pixels 27" display was used with a standard computer mouse for control inputs.
Figure 1. Simulator interface, with blue aircraft allocated to au-
tomation and green aircraft to the human ATCO. Background col-
ors have been inverted here for clarity.
Figure 2. Callsign menu,
as shown when clicking the
callsign in an aircraft label.
The ATCO could delegate
a ﬂight to automation by
pressing "ASSUME TO
AUTO". Once the ﬂight
was assumed, a "TRANS-
FER" button was added to
Airspace and Traﬃc Scenario
Participants were responsible for traﬃc above FL245 in the combined DELTA and
JEVER sectors, above the Netherlands and part of Germany. Each ATCO experienced the same
traﬃc scenario, resembling an average day in February 2020 (prior to the COVID-19 pandemic).
There were between 15 and 30 ﬂights in the sector at any time (M = 21, SD = 4). Flights followed
standard routing or directs to their designated exit points. Besides overﬂying traﬃc, arrivals and
departures to several airports, within or close to the sector, were included. There was no wind.
During the exercise, the ATCOs were accompanied by an automated “colleague". When
ﬂights entered their sector, the ATCOs had to decide whether to manually assume the ﬂight or
delegate it to automation (Fig. 2). This allocation remained ﬂexible, such that they could re-
assume manual control or delegate ﬂights to automation at any time, anywhere in the sector. All
ﬂights had to be manually transferred to the next sector, including those delegated to automation.
Automation was capable of performing the following tasks:
•Ensure suﬃcient separation between automated aircraft (5 NM, 1000 ft),
•Deliver aircraft at their exit point and transfer level, descending as late as possible, and
•Descend arrivals to FL260 to be transferred to lower area control.
When two automated aircraft encountered a conﬂict, it was always solved in the vertical
plane. Automation would never issue any heading commands or direct-to’s. In case of a human-
automation conﬂict, it was up to the ATCO to solve it, under the presumption that automation
would not know the ATCO’s intents. Apart from showing the clearances in the aircraft labels,
automation did not provide any feedback on its intentions.
After signing a consent form, each participant received a ten-minute training, during
which the automation was introduced and participants familiarized themselves with the interface.
Both a human-automation and automation-automation conﬂict were shown to demonstrate how
automation would handle both situations. The training was concluded with a short questionnaire.
Next, the measurement run started with a ﬁve-minute take-over period, during which no
commands could be issued, followed by 90 minutes of real-time simulation. Each ATCO was
subjected to one allocation suggestion scheme (Table 1), based on ﬂight type or entry sector. The
suggestions were shown by the label color upon sector entry (green = manual, blue = automated),
but the ATCOs were not told which scheme was applied to them. In all cases, they could ignore
the suggestions and re-allocate each ﬂight at any time, even after delegating it to automation.
Throughout the run, an observer asked the ATCOs to explain their actions and what they
were taking into consideration. Every three minutes, the ATCOs rated their instantaneous work-
load by clicking on an on-screen 0-100 scale. After the experiment, they completed an extensive
questionnaire, followed by a radar replay allowing speciﬁc situations to be reviewed.
Table 1. Suggested human-automation ﬂight allocation strategies.
ATCO Basic traﬃc Complex traﬃc DELTA JEVER
1 Human Automation - -
2 Automation Human - -
3 - - Human Automation
4 - - Automation Human
5 Human Human Human Human
6 Automation Automation Automation Automation
Note. Basic traﬃc has to descend/climb 2000ft or less in the sector. All other traﬃc is labelled as complex.
Results and Discussion
All ATCOs delegated at least 50% and up to 100% of traﬃc to automation, regardless of
the suggested allocation (Fig. 3). Whereas most ATCOs largely ignored the suggested allocation,
ATCO-3 tried to follow it when he realized that one of the sectors was completely handled by
automation. He even delegated/assumed ﬂights as they crossed the border between the two sec-
tors, commenting that solitary manual ﬂights in a predominantly automated area were diﬃcult to
handle. The big drop in automation observed for ATCO-4 around 50 minutes, was caused by him
purposely re-directing ﬂights manually to “test automation” with a more complex scenario. He
stated that he would have been okay with purely monitoring a completely automated scenario.
Figure 3. Time traces of the fraction of ﬂights allo-
cated to automation (red). The blue line shows the
fraction, if the ATCOs would have followed the sug-
gested allocation on airspace entry (see Table 1).
0.01 0.5 0.75 1
Min. fraction of ﬂight automated
Share of ﬂights
Threshold Basic Complex
Figure 4. Cumulative share of ﬂights
that was delegated to automation for a
minimum fraction of their duration, as
a function of level change threshold.
When asked about all allocation strategies from Table 1, the ATCOs unanimously agreed
that complex ﬂights, here deﬁned as requiring more than 2,000 ft level change, need to be han-
dled manually (potentially with support tools). They indicated a strong preference for delegating
basic ﬂights to automation, which is for most ATCOs also reﬂected in the time that they delegate
such ﬂights to automation (Fig. 4). Although some ATCOs said 5,000 ft would have been a more
appropriate choice of level change threshold, at which traﬃc was divided in basic and complex,
this is not directly reﬂected in the ﬁgure. All traﬃc that had to change levels has evoked more
manual control than overﬂights with zero level change and could thus be considered “complex”.
Apart from this division into basic and complex traﬃc, the questionnaire provided more
insight into how ATCOs determined whether ﬂights should be delegated or not (Fig. 5). Traﬃc
directly around the ﬂight was especially important when there were many manual ﬂights and del-
egating a single ﬂight to automation would have added (too) much uncertainty. The suggested
allocation was given low priority, or ignored by most ATCOs (except ATCO-3), as conﬁrmed by
Fig. 3. In general, ﬂights were assumed manually, sent on a direct to their exit point and only del-
egated to automation when clear of conﬂicts, irrespective of the suggested allocation. If automa-
tion would have been capable of giving directs, the ATCOs would have delegated more ﬂights.
Traﬃc directly around the aircraft
The type of ﬂight
Traﬃc along the route of the aircraft
Capabilities of automation
The suggested allocation
The route of the aircraft
Flight level of the aircraft
The distance of the aircraft to the next sector
Figure 5. Driving factors that made ATCOs decide to delegate ﬂights to automation, or not.
Trust in Automation
At the start of the experiment, all ATCOs reported to have a high level of trust in automa-
tion in general (Fig. 6). Nonetheless, they were suspicious of the experimental automation after
the (short) training. Throughout the 90-minute run their trust increased considerably, according
to the ATCOs mainly due to seeing the automation perform well. The rule-based form of au-
tomation (programmed to be “perfect”), clear separation of responsibilities and absence of un-
certainties, such as wind and pilot behaviour, further contributed to this. ATCOs did, however,
not like the lack of feedback, a common pitfall in automation design hindering the establishment
of human-automation teamwork (Norman (1990)). As automation did not indicate where or when
it would descend aircraft, ATCOs sometimes assumed aircraft manually, solely to prevent them
from descending unexpectedly. All ATCOs would have liked automation to at least show its in-
tentions about where on the trajectory it would start and end a climb or descent.
I trust automation (pre-experiment)
I trust the automation (post-training)
I trusted the automation (post-experiment)
Neither disagree nor agree
Figure 6. Trust in automation as reported by the ATCOs.
While this experiment focused on aircraft allocation, a human-automation team may also
be created by sharing tasks. Four out of six ATCOs included the capabilities of automation in
their allocation strategy (Fig. 5). We replicated part of the study from Prevot et al. (2012), to
see what kind of tasks the ATCOs would like to do themselves, share with automation or com-
pletely delegate to automation. In line with the ﬁndings of Prevet et al., the ATCOs indicated
that a considerable number of tasks can be either shared with or completely delegated to automa-
tion (Fig. 7). Transfer of control can be automated as a ﬁrst step towards more automation, but
ATCOs should be able to reject auto-transfers as well as to initiate early transfers. The ATCOs
prefer to keep short-term, tactical actions manual, while more strategic long-term planning and
routine tasks can be (partially) delegated to automation. Presumably this is because automation
can introduce too much uncertainty in critical short-term situations.
Changing display range (zoom)
Approving weather reroutes
Solving short-term conﬂicts
Issuing climbs and descends
Coordinating with neighbouring controllers
Solving medium-term conﬂicts
Detecting short-term conﬂicts
Transfers of control
Detecting medium-term conﬂicts
Moving labels (decluttering)
Figure 7. Allocation of tasks between human and automation as desired by the ATCOs.
All ATCOs classiﬁed their situation awareness as “okay”, the middle score on a ﬁve-point
Likert scale from “poor” to “very good”. Several mentioned that they paid less attention to the
blue automated aircraft, akin to transferred ﬂights, even though they were still responsible for
these ﬂights. At the only (not explicitly programmed) occurrence of a human-automation con-
ﬂict in the experiment, the involved ATCO was surprised by the short-term collision alert and ex-
plained that he had not seen the automated aircraft as it was emerging from, in his words, “a sea
of blue aircraft”. Future experiments with eye trackers could give insight in changing scanning
patterns when aircraft are delegated.
This exploratory study gained useful insights into human-automation teaming in a real-
istic ATC setting. We showed that professional en-route ATCOs are not averse to sharing their
work in a sector with automation. In a simpliﬁed situation, lacking uncertainties by wind, emer-
gencies and pilot requests, a high level of delegation to automation was reached, under the con-
dition that ﬂights were on direct routes and free of conﬂicts. ATCOs generally ignored the sug-
gested allocation, suggesting a need for a diﬀerent allocation scheme that may be more accepted.
Future research should take a closer look at determining speciﬁcally which ﬂights should
be considered “basic” or “complex”, such that a ﬁtting allocation scheme can be applied. Addi-
tionally, the inﬂuence of environmental uncertainty (e.g., wind and pilot delays) and automation
capabilities should be researched. Together with empirical studies on the various forms of task
sharing and distribution, this can help establish human-automation teamwork in a shared ATC
The authors would like to express their gratitude to all participating ATCOs, as well as to
MUAC for facilitating an experiment in these challenging times of COVID-19.
Bainbridge, L. (1983). Ironies of Automation. Automatica,19(6), 775–779. doi: 10.1016/0005-1098(83)90046-8
Birkmeier, B., Tittel, S., & Korn, B. (2016). Controller Team Possibilities for Sectorless Air Traﬃc Management. In
ICNS 2016: Securing an Integrated CNS System to Meet Future Challenges (pp. 3–1). Herndon, VA, USA:
IEEE. doi: 10.1109/ICNSURV.2016.7486362
Metzger, U., & Parasuraman, R. (2005). Automation in Future Air Traﬃc Management: Eﬀects of Decision
Aid Reliability on Controller Performance and Mental Workload. Human Factors,47(1), 35–49. doi:
Norman, D. A. (1990). The ’Problem’ with Automation: Inappropriate Feedback and Interaction, not ’Over-
Automation’. Philosophical transactions of the Royal Society of London. Series B, Biological sciences,
327(1241), 585–593. doi: 10.1098/rstb.1990.0101
Prevot, T., Homola, J. R., Martin, L. H., Mercer, J. S., & Cabrall, C. D. (2012, 2). Toward Automated Air Traﬃc
Control-Investigating a Fundamental Paradigm Shift in Human/Systems Interaction. International Journal of
Human-Computer Interaction,28(2), 77–98. doi: 10.1080/10447318.2012.634756
SESAR Joint Undertaking. (2019). European ATM Master Plan - Digitalising Europe’s aviation Infrastructure. doi: