Description

Track label filtering is an ATS system feature that (temporarily) hides the labels of tracks that are considered to be unconcerned to the controller. Note that while labels can be hidden (filtered), the track symbols themselves must be presented at all times as stipulated in ICAO Doc 4444. Also, as emergency transponder codes (7500/7600/7700) must be presented to the controller, the labels of these aircraft are not suppressed.

The goal of track label filtering is to achieve optimal balance between hiding unimportant data and presenting what the controller needs to see on the situation display.

As with any other system feature, unexpected operation or inappropriate setting of the filter does not release the controller from their responsibility to provide safe ATS.

Use Cases

The following is a (non-exhaustive) list of situations where it is considered appropriate to filter out the labels of some tracks that are:

• above or below the area of responsibility. This is applicable for vertically split area control sectors (e.g. upper and lower) as well as for approach control units (which can be treated as lower sectors in this context).
• representing specific flights (e.g. military aircraft participating in an exercise in an SUA)
• correlated but unconcerned (i.e. are not expected to enter or to fly in close proximity to the sector)
• uncorrelated. Normally these are associated with flights that are not expected to enter the sector.

Benefits

Generally, filtering the unconcerned labels allows the controller to focus on the important aircraft, i.e. those that are in, are about to enter, or have just left their area of responsibility. Associated benefits include:

• reduced clutter. Less data on the situation display means that there are fewer distractions on the screen. See pictures below as an example.
• reduced workload due to reduced need to move track labels. Part of the routine tasks of a controller is to make sure the track labels are not overlapping. Since aircraft move, the associated labels also move so controllers need to constantly adjust the labels in a way that there is no overlap.
• ability to use a larger range setting. This applies mostly to situations with multiple vertically split sectors. Generally, using a larger range setting increases the controller's situational awareness as they can see the traffic well in advance and plan accordingly. However, if the display becomes too saturated due to multiple labels associated with aircraft in upper or lower sector(s), controllers may be forced to reduce the visible range so that they can arrange the labels without overlapping. Filtering the unconcerned labels out is an option to provide more free space on the screen.

Risks

Notwithstanding the benefits associated with label filtering, there are some inherent risks to be considered by system designers and air traffic controllers. Those include:

• reduced situational awareness due to the reduced amount of information on the screen. While sometimes less data is beneficial (fewer distractions as mentioned above) in other circumstances it could turn out that some important detail is not visible on the screen. This could happen for variety of reasons, e.g. sub-optimal design of the function that failed to consider certain scenarios, controllers not adjusting the flight trajectory in time or a controller's rushed response to a pilot request without considering that the clearance involves another sector. While the scenarios involving controller behaviour pose a risk regardless of the use of label filtering (due to the unconcerned colours used), this effect can be further aggravated by hiding the label information.
• reduced time for situation assessment. Sometimes an unconcerned traffic turns into one that affects the sector. Using a filter could delay the discovery of such a situation and reduce the available time for handling.
• increased risk of missing a conflict. This could happen as a consequence of reduced situational awareness and reduced time for reaction described above. Normally the risk is mitigated by carefully desinging the operation of the filter function and by designing appropriate operating procedures for air traffic controllers. See pictute below as an example.
• coordination difficulties. If the controller receives a coordination phone call about an aircraft that is currently filtered out, it will be more difficult to find it and consequently, the coordination will be prolonged. This can happen with both inter-unit and intra-unit coordinations.
• sometimes it is difficult to find the aircraft that just called on the frequency. Normally, all aircraft that are within or are about to enter the controller's area of responsibility are not subject to label filtering. However, an aircraft that is not about to enter the sector may contact the controller due to e.g. a mishandled frequency change. While this is a challenging scenario in general, using a filter would aggravate the situation as the controller would need to put extra effort in identifying the aircraft.

Defences

Defences against the risks associated with the use of label filtering fall into two broad categories:

• System design
  • Easy and intuitive way to switch the filter off. This allows the controller with a way to quickly get access to all available information.
  • Easy and intuitive way to show a hidden label (e.g. temporary displaying it when the mouse cursor hovers over the track). See picture below as an example.
  • Filtering not available for certain flights (e.g those that are scheduled to enter the sector, regardless of their current level).
  • Appropriate options for adjustment. For example, the vertical filter setting may be implemented in a way that prevents the controller from accidentally filtering out traffic at neighbouring levels (e.g. within 2000 ft above or below their area of responsibility).
  • Filter inhibition, i.e. overriding the filter settings and displaying the label in some situations such as aircraft being physically in the controller's area of responsibility (regardless of label colour), aircraft squawking an emergency code, etc. See picture below as an example.
• Controller behaviour
  • Adjust the filter in accordance with local procedures.
  • Be aware of the risks and limitations associated with the use of filtering.
  • Before initiating a coordination, take a moment to assess what picture is presented to the other controller. Sometimes there is an option to highlight the flight that is subject to coordination, e.g. via a dedicated feature (for intra-unit coordination) or by manually sending an OLDI message (when coordinating with a neighbouring ATS unit).
  • Updating the aircraft trajectory (e.g. in case of a direct routing clearance, vectoring or weather avoidance) so that the sector sequence is properly updated and the labels are represented in appropriate colours to the affected sectors. This may also exclude a label from the applied filter in a neighbouring sector, if the aircraft is no longer considered "unconcerned".
  • During the handover-takeover process, inform the relieving controller that a filter is being applied in case this is not a standard practice.