Keywords

1 Introduction

The goal of the Next Generation Air Transportation (NextGen) system is to introduce new tools and concepts of operations that will accommodate the projected increase in air traffic in the National Air Space (NAS) [1]. To ensure safety in the current system, each airspace sector has a maximum number of aircraft that are allowed to enter the sector [2]. The reason for this limit is to ensure that cognitive resources of air traffic controllers (ATCos) are not exceeded, as this would produce an unacceptable amount of workload, and therefore compromise safety [2]. To accommodate the projected increase in traffic density, NextGen has proposed the introduction of new automation tools that will assist ATCos in handling more aircraft while keeping cognitive workload at an acceptable level.

Datalink or data communications is one NextGen tool that is designed to help ATCos manage more aircraft in their sector. Datalink allows both vertical and lateral conflict resolutions and trajectory changes to be communicated between pilots and air traffic controllers through non-verbal methods. As such, Datalink can decrease the amount of miscommunication on the party line because only the intended recipient will receive the message, and the message, being shown on a visual display, can be referenced at a later time. Datalink can also decrease the working memory load of pilots because the system can be integrated with the flight management system of the aircraft, and the pilot can simply execute the appropriate clearance. Datalink is also likely to be implemented with other automation tools designed to reduce ATCo workload. One tool is conflict detection, which alerts the ATCos when two Datalink equipped aircraft are in conflict prior to a loss of separation. Conflict detection will reduce the need for ATCos to scan the radar display for conflicts. Another tool is the conflict probe that would alert an ATCo if potential route changes using a third tool, the trial planner, would result in new conflicts [3].

Prevot et al. [4] conducted a study that examined whether ATCos can successfully employ Datalink for managing conflicts in their sector. Air traffic control participants were tested under three levels of simulated traffic density: 1X (current traffic density), 2X (twice the current traffic density), or 3X (three times the current traffic density). Prevot et al. found that ATCos were able to use the Datalink tools effectively, and that Datalink tools were most beneficial to the ATCos when the traffic density was 2X and 3X compared to current day traffic levels.

Although Datalink offers ATCos the benefits described earlier, it also has drawbacks. ATCos are typically slower at issuing Datalink clearances because they must navigate through computer menus to give a command rather than voicing the clearance [5]. The delays in Datalink communications may also not be acceptable when clearances need to be executed immediately. Additionally, although Datalink reduces party chatter, it also eliminates the immediate feedback of the pilot acknowledging the clearance. This may compel the ATCo to be more vigilant when monitoring the radar to make sure clearances were indeed executed appropriately. Because traditional voice communication between ATCo and pilot provides immediate feedback that the pilot received the clearance (correctly or incorrectly), it may be preferred in times of urgency.

In present study, we examined what communication method student controllers preferred when they were learning how to manage traffic. Data from 4 semesters of students participating in a radar internship at the Center for Human Factors in Advanced Aeronautics Technologies (CHAAT) were analyzed. We wanted to answer the following questions: In general, do students prefer to use Datalink or Voice to resolve conflicts? Does the preferred method change over a semester of training? Are there situations where Datalink is specifically helpful in assisting conflict resolution?

2 Methods

2.1 Participants

A total of 50 air traffic controller students’ data were included for analyses from four semesters of data collection over the period of Fall 2011 to Spring 2013. Demographics were available for 44 participants. There were 37 males and 7 females, and the mean age of the students was 24.75 yrs, with a standard deviation of 2.74 yrs.

2.2 Simulation Environment

Participants were tested and trained on scenarios using the Multi Aircraft Control System (MACS) software, a medium-fidelity simulator [6]. MACS simulated Indianapolis Center (ZID-91), which includes overflights as well as departures from, and arrivals to, Louisville International Airport. Aircraft in the sector were piloted by other students in the class during the semester who were trained to make flight changes using simplified menus provided by MACS. The NextGen equipped aircraft included the following tools: trial planner, conflict probe, and Datalink. The conflict probe uses algorithms to detect conflicts between pairs of Datalink equipped aircraft. Datalink is a digital communication tool that allows ATCos to digitally handoff, change frequency, and deliver various clearances to aircraft in a text-based format. The trial planner is a tool that allows ATCos to make changes in the aircraft’s route visually on the radar display by “clicking and dragging”. The route change can uploaded directly to the aircraft’s flight management system through Datalink.

2.3 Procedure

Each internship class consisted of 3.25 h of radar simulation training and 1.5 h of class lecture. A retired, radar-certified air traffic controller taught all components of the internship. In the first 8 weeks of the internship, students were instructed on basic air traffic management techniques, such as issuing speed, altitude, and heading clearances. Students were tested twice, once at the midterm and once at the end of the internship (i.e., the final test). For each test session, participants were tested on scenarios that consisted of 0 %, 50 %, and 100 % Datalink equipped aircraft. The data included in the present study is only from the 50 % equipage scenarios from the midterm and final exam because those scenarios were the only scenarios in which participants would issue both voice and Datalink clearances. In the 50 % scenario, there were 2 planned conflicts between a Datalink equipped and non-Datalink equipped aircraft. How the students resolved these planned conflicts were evaluated to answer some of our research questions.

2.4 Data Coding

To answer the question of which method ATCo students used to resolve conflicts, we recorded whether the ATCo student moved the Datalink equipped or unequipped aircraft to solve the conflict. If the students moved the Datalink equipped aircraft, this would indicate that they preferred to resolve the conflict using Datalink. Conversely, if the students moved the unequipped aircraft, this would indicate that they preferred voice.

Students were also asked about their preference for using Datalink versus voice in a debriefing session that occurred after the final exam. In particular, there were two questions concerning preference between voice and Datalink that were analyzed through content analysis. The first question was “Which method did you prefer to solve conflicts?” The second was, “Are there tasks that are specifically difficult to perform without Datalink?” To assess inter-rater reliability, two researchers categorized the answers independently. The agreement rate was 98 %. For the 3 discrepancies out of the total 150 questions, a third rater resolved the discrepancy.

3 Results

As with any study examining data collected in courses over multiple semesters, slight differences in the instruction and testing were evident across the semesters. Due to this, we set our alpha level at .10 for a more liberal criterion. However, all students included in this analysis were trained on air traffic management with both Datalink and voice over a course of 16 weeks.

3.1 Which Communication Method Do Student ATCos Use More Often to Solve Conflicts?

To assess which method ATCo students use more often to solve conflicts, and if this changes over time, a Chi-square contingency test found that preference for moving aircraft with voice or Datalink changed between the midterm and final exam, χ 2 = (1, N = 95) = 2.879, p = .090. Participants moved more aircraft using Datalink than voice at the midterm, but at the final, the number of voice and Datalink clearances was roughly equal, as shown in Table 1.

Table 1. Number of Datalink and Voice Aircraft Moved to Resolve Conflicts at the Midterm and Final.
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3.2 Which Communication Method Do Student ATCos Prefer to Use to Solve Conflicts?

As shown in Fig. 1, more students preferred to solve conflicts using voice (52 %) compared to Datalink (20 %). For the participants who indicated, “It depends” (12 %), they stated preferring using Datalink for conflicts that were further out and voice when the conflict was perceived as closer.

Fig. 1.
figure 1

Proportion of responses for preferred method of conflict resolution

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3.3 Are There Tasks that Are Specifically Difficult to Perform Without Datalink?

As shown in Fig. 2, 54 % of the student ATCos indicated that vectoring was more difficult to perform without Datalink. Because conflict detection was only available between two Datalink equipped aircraft, 16 % of the students also indicated that detecting conflicts was more challenging without Datalink.

Fig. 2.
figure 2

Proportion of responses for tasks that are difficult to perform without Datalink

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4 Discussion

The main goal of our study was to examine student ATCos’ preferences between traditional voice-based communication and Datalink, which method they use more often to solve conflicts, and if this changes over a semester of training. In terms of performance, we found that students were more likely to use Datalink during their midterm (after 8 weeks of training), but at the final, they used Datalink and voice equally often. The early preference for Datalink observed during the mid-term may be a result of the students relying on advanced tools to help them with air traffic management while becoming proficient with voice communications.

When students were directly asked which method they preferred during the debriefing session, more students indicated that they prefer voice over Datalink. The preference for voice over Datalink may be due to the fact that once phraseology is mastered, voice communications can be faster than Datalink [5]. Some students responded that “it depends”. For these students, they indicated favoring Datalink when the conflict was farther out and voice if the conflict was closer, again suggesting that the main benefit of voice was that it was a more efficient method of managing traffic. As mentioned earlier, sending a Datalink message typically entails a longer waiting period for the ATCo to know that the pilot acknowledged the clearance, which may compel ATCos to use voice based communications in times of urgency.

We also wanted to determine if there were any situations where Datalink might be favored. In the debriefing, the majority of ATCo students indicated that vectoring was more difficult to do without Datalink. When an ATCo gives a vector by voice, it can involve multiple calls to the pilot, giving them heading vectors and then putting them back on their original flight plan. This process can be taxing for the ATCos. Moreover, many ATCos indicated that vectoring is much easier to do with Datalink because they can visualize the route when using the trial planner that was implemented in the studies we analyzed.

In summary, we found that students were more likely to use Datalink to solve a conflict during their midterm than at their final exam. At the final, though, no performance difference was found. The majority of students reported favoring voice over Datalink to solve conflicts. However, even among students who preferred voice, many ATCo students saw the benefit of using Datalink to give trajectory changes to aircraft. It is important to note that the data from our study is from ATCo students, and that preferences for ATCos who have been working in the field may be different.