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OPAS tracks departing aircraft through eight distinct operational segments, five defined by selection zones and three by time of exit and entrance to adjacent zones.

1. Understanding the On Stand segment

The On Stand segment marks the start of departure operations and represents the opposite of an arrival. OPAS detects this segment using a combination of a GIS polygon layer of the airport and allocated stand data from the flight plan.

To create the On Stand segment, OPAS follows this process:

1. Detect radar points within the stand area.
2. Identify when the aircraft exits the stand.
3. Create a start time five minutes before the segment ends (when the aircraft leaves the area).

Note: If accurate radar data cannot be collected, OPAS will refer to the On/Off blocks data in the flight plan.

2. Understanding the Taxi segment

The Taxi segment represents the time between exiting the On Stand segment and entering the Stop Bar to Runway segment. OPAS calculates this segment similarly to the Arrival Taxi segment, as it captures the transition between adjacent segments.

OPAS creates Taxi segments in this manner because there are too many variables in how an aircraft is directed through the airport to its designated runway entry point. Some Stationary segments may be created inside the Taxi phase for further analysis.

3. Understanding the Stationary segment

OPAS creates a Stationary operational segment whenever an aircraft radar track shows as stationary for more than a configurable number of seconds. This segment serves as an analytical tool to identify disruptions during the Taxi phase.

When the track shows movement again, the Stationary segment closes and Taxi resumes. Both segments run simultaneously, with Stationary segments used to analyse whether the Taxi phase was disrupted.

Note: Stationary segments can occur inside any segment where the aircraft must wait, meaning they will always be shorter than the total time spent in that segment.

4. Understanding the Dwell at Stop Bar segment

The Dwell at Stop Bar segment is a discrete segment of the taxi phase created to analyse potential congestion at the runway entrance. These segments appear in yellow in the image above, next to the red Stop Bar to Runway Entrance segments for visual reference.

Time spent in this segment contributes to both the Dwell at Stop Bar totals and the Taxi time. This can potentially lead to totals being added to three segments simultaneously: Taxi, Stationary and Dwell at Stop Bar.

5. Understanding the Stop Bar to Runway Entrance segment

The Stop Bar to Runway Entrance segment consists of selection zones covering every possible runway entrance point. These zones begin at the stop bars and end on the runway border.

When an aircraft enters this segment, it signifies the end of the Taxi segment. Operationally, this indicates the aircraft is using the runway and no other operation will use it until the aircraft has departed. Segment times are typically short as the aircraft rolls through to the runway.

6. Understanding the Runway Entrance to Line Up segment

This transitional segment captures runway entrance and occurs between the Stop Bar to Runway Entrance and Start of Roll to Wheels Up segments. OPAS expects one zone for every possible entry point on the runway.

Each small zone is partnered with a Stop Bar to Runway Entrance zone. Transit time in this segment is typically brief, as it represents the last segment before actual runway use.

7. Understanding the Dwell at Line-Up segment

These zones capture the moments immediately before Start of Roll, before throttle is applied. One zone is required for each runway entry point, as the aircraft may enter and pause at any point of the runway, departing in either direction.

8. Understanding the Start of Roll to Wheels Up segment

The Start of Roll to Wheels Up segment represents the full throttle takeoff phase. One zone should be defined for each runway entrance.

The Start of Roll zones start just in front of each lineup point for each runway entrance. To track this segment, OPAS follows this process:

1. Detect when the aircraft begins the roll and penetrates the zone.
2. Track the segment time until wheels up.

Note: Most zones are constructed with a relatively high ceiling to avoid anomalous points, but these zones are set at a ceiling of 50 feet to ensure the segment end time more accurately reflects wheels up.