Lowest level Pattern Identification
Lowest level patterns apply to individual aircraft; they address the maneuvers in horizontal,
vertical, and speed. Once these maneuvers are identified, it becomes possible to interpret them in the
context of the aircraft's intended route and to infer Air Traffic Controller's instructions
(Direct
to a given Waypoint, for instance).
Identification of horizontal and vertical maneuvers
The figure to the left illustrates the trajectory of a landing aircraft in horizontal (top figure) and in vertical (bottom figure). The data are obtained from air surveillance, and we see how maneuvers are determined in horizontal and vertical. Maneuvers (turn and vertical evolution) are in red, and straight portions (straight lines in horizontal, level off in vertical) are in green. The beginning and end of each maneuver are illustrated by small grey squares. The accuracy of our algorithms can be appreciated by .
Small maneuvers are well identified, both in horizontal and vertical.
Identification of speed maneuvers
Speed maneuvers are of two kinds: constant Mach above a certain altitude, and constant
Indicated Air Speed (IAS) below. The left part of the figure illustrates the identification
of
constant IAS maneuvers, based on positional air surveillance data. From positional data, we proceed
by
computing the ground speed (by derivation), and we approximate this ground speed with the air speed
(which adds a wind speed noise). This noise is visible on the raw positions in the figure.
The right part of the figure illustrates the identification of Mach maneuvers. MACH maneuvers are
expressed in percentage of MACH, so a value of 60 represents a Mach 0.6. Do you see how MACH and
IAS
maneuvers can be combined?
The first MACH maneuver (under the red ellipse, corresponding to Mach 0.8) is more explanatory than
the
corresponding IAS maneuvers, so we retain it. Then we switch to IAS maneuvers. See the next
paragraph
(speed schedule) for a more detailed presentation.
Identification of a speed schedule
We now explain how IAS and MACH maneuvers are combined. A first step is illustrated on the left, for
the
aircraft trajectory of the previous figure. Constant IAS maneuvers are
in
blue, constant MACH maneuvers are in green, and IAS evolution maneuvers are in red. We notice that the level off vertical maneuvers have also been
added
to the speed maneuvers, so as to distinguish whether the aircraft is steady or in vertical
evolution:
.
Then, we derive a speed schedule, which is a profile of the speed with regards to the
altitude:.
The speed schedule exhibits jumps, when the aircraft keeps vertically steady whereas the speed varies. Nevertheless, the speed schedule is a good way to model the speed profile of the aircraft when implementing other scenarios, as we will see later.
The next layer: identification of controller's instructions
We now detail the level "just above" the previous one. Once the maneuvers have been identified, it becomes possible to identify air traffic controllers' instructions. To do so, it is necessary to have as input the flight plan route followed by the aircraft. From this flight plan route together with the surveillance data, a preliminary work consists of identifying the procedures followed by the aircraft (SID, STAR, APCH). We do not detail this process here. Once the flight plan route together with the procedures are available, we can infer the air traffic controllers' instructions from the aircraft maneuvers.
Identification of horizontal Instructions (introduction)
We start with a simple introductory example which shows how to identify an instruction of the kind
"Direct towards a Waypoint". The figure to the left illustrates, in horizontal, the
trajectory
of an aircraft together with its flight plan route. When a turn is , we identify this turn as
resulting from an air traffic controller's instruction, namely a Direct toward this waypoint.
Identification of horizontal Instructions (general case)
In practice, we need to distinguish whether the aircraft follows its flight plan route (in which case, there is no point in interpreting the turns as resulting from controllers' instruction), or the turn occurs "sufficiently far" from the flight plan route (in which case, this turn does not result from the avionics and we can interpret it as resulting from a controller's instruction). The figure to the left illustrates the two cases: When the aircraft , we do not infer the turn as resulting from the air traffic control. However, if the turn occurs "not at a waypoint" and "aiming further than the next waypoint" then we identify this turn as , namely a Direct toward this waypoint.
Operational interpretation of horizontal Instructions
We have seen, in the previous examples, how to interpret a turn based on where the turn is
aiming
to (the red dashed line in the previous figures). If this red dashed line is heading
towards a
waypoint, then (as we have seen) the turn is interpreted as a Direct towards that Waypoint. There
are
actually other cases than this one, but the principle remains the same, as we now explain.
Actually, if the red dashed line (showing where the turns aim towards) does not aim at any
waypoint, then we interpret the turn as a Turn To Heading (e.g. Turn to Heading 240). It is
interesting to notice that "where the turn aims to" provides an insight into the outcome of
the
instruction, namely: did it shorten (or lengthen) the route? The figure to the left provides
an
example of the latter. We see that when
in the flight plan route, then the outcome of the instruction was to deviate from the route
(and lengthen it).
Similarly, we can also identify when the controller instructs the pilot to
.
As we can imagine, deviations from the intended route result from conflicts with surrounding
aircraft
(either in crossing or in sequencing), which forces the air traffic controller to deviate one
aircraft
from its route, with an additional length on the flight route. We will detail this in the higher level patterns.
Recognition and Operational Understanding of Additional Air Traffic Controller Actions
Similarly, vertical instructions can be identified. In this context, they possess an operational
interpretation
based on the aircraft's airspace design. As demonstrated in our introductory
example, the vertical profile of an aircraft is intricately connected to the vertical
constraints of
each Control Position that the aircraft encounters, leading to specific vertical instructions to adhere
to these
constraints.
This underscores the importance of identifying the entry and exit of the aircraft into the
successive Control Positions. This identification process is facilitated by geometric algorithms, with
each
Control Position being a compilation of specific air traffic sectors at a given time. While we won't
delve into
this level of detail, it's crucial to note that the air traffic control's identification of instructions
encompasses the transfer of control from one Control Position to the next. In essence, our
identification
of instructions enables us to monitor which controllers are overseeing which aircraft at
any
given moment.