Enhancing Safety Through the Use of Data Link

by Richard Sletten, Manager, ACC Operations, Edmonton, NAV CANADA

The Arctic High Specialty in the Edmonton area control centre (ACC), in some ways, represents the future of air traffic control (ATC) and management today. Data link, and its integration into controller decision-making tools, has been a big part of the automation to assist ATC in performing their daily tasks and in greatly reducing safety incidents (pilot and controller). Data link refers to controller–pilot data link communications (CPDLC) and automatic dependent surveillance —contract (ADS-C).

Controller–Pilot Data Link Communications—CPDLC

Controller–pilot data link communications is analogous to ‘texting’ between ATC and pilots, using equipment interfaces between the controller’s situational display and the flight management computer on the flight deck of an aircraft. In the Arctic High Specialty, all CPDLC clearances, whether pilot or controller initiated, are tested for air traffic conflicts prior to the clearance being uplinked to a flight deck. A Medium Term Conflict Detection is evaluated for surveillance separation; simultaneously, conflict prediction evaluates for procedural (non-surveillance separation), and the controller is alerted prior to the clearance being ‘uplinked’. The Edmonton Arctic High Specialty supports requests and clearances for altitude and route.

As illustrated in Figure 1, UAL803 is requesting Flight Level 360. When the controller actions the request and the requested altitude is selected, it is tested by default. The green ‘Submit’ button indicates the flight would not be in conflict if the clearance is issued.

If a conflict was detected, the Submit button would display yellow or red based on the time proximity of the conflict, and a graphical display would result, as indicated in the example involving QTR39A (Figure 2).

When a pilot makes a request and the requested ATC clearance is selected and actioned, using our respective interfaces, the minimal manual intervention greatly reduces the incidence of human error. Readback hearback errors are eliminated, and safety is greatly enhanced.

CPDLC Route Conformance Monitoring

CPDLC route conformance monitoring is also being used within the Edmonton Arctic High Specialty to alert ATC of a potential route deviation in advance of the deviation occurring.

When an aircraft comes into Edmonton airspace, an uplink message, ‘Confirm Assigned Route’, is sent using CPDLC. When the flight responds, the received route is compared to the route as filed. If the received route matches the filed route, no alert is provided to ATC, and no action is required. If the CPDLC received route is determined to not match the filed route, then an indication is presented to ATC on the flight data tag, and the non-conformant portion of the route is highlighted, as illustrated in the VIR20V example (Figure 3).

ATC can then intervene to ensure the route in the flight management computer matches that held by ATC, ensuring the Conflict Detection algorithms are being tested against an accurate flight profile.

Flights will not be queried on their route if within 30 minutes of top of descent and further modifications are ongoing to ensure this request occurs to reduce unnecessary request for routes that may be considered onerous by flight crews.

Automatic Dependent Surveillance—Contract–ADS-C

The Edmonton ACC will establish event and periodic ADS contracts with suitably equipped flights operating in ADS-C designated airspace.

Event contracts are received when a flight progresses to a waypoint or amends its route, while a periodic contract is to be received every 11 minutes.

The ATC system evaluates the current waypoint and next two successive waypoints, the reported altitude and the implied accuracy of the report. If the report is conformant, the report is sent to ‘History’, and no action is required by ATC. If the report is non-conformant, an alert is provided to ATC with the non-conformant information highlighted. The ADS-C times also will indicate a detected conflict, if coloured yellow or red.

ADS-C reports work to ensure that the flight profile in the flight management computer matches the profile held in the ATC system, as it is the profile that is evaluated in reporting traffic conflictions to ATC. Additionally, with GPS jamming becoming more of a worldwide concern, the figure of merit (FOM) is reported to assist ATC in increasing separation when the navigational capabilities of an aircraft have been compromised.

The use of data link capabilities has been essential in the Arctic High Specialty, promoting:

• user preferred flight trajectories;

• increased system efficiency; and

• increased safety by reducing potential safety incidents.

Data link assists ATC by integrating system conflict detection into ATC and by providing appropriate alerts at the appropriate time for ATC to react and investigate to ensure the overall safety of the air traffic management system.