Note: Descriptions are shown in the official language in which they were submitted.
256525A
SCHEDULE MANAGEMENT SYSTEM AND
METHOD FOR MANAGING AIR TRAFFIC
BACKGROUND OF THE INVENTION
[0002] The present invention generally relates to methods and systems for
managing
air traffic. More particularly, this invention relates to methods and systems
used to
optimize air traffic control operations and minimize losses in air traffic
efficiency, and
includes methods and systems for managing the time schedule for arriving
aircraft by
including early cruise descents as a means of absorbing time delays resulting
from one or
more aircraft missing its/their scheduled time of arrival (STA).
[0003] Managing the time schedule for aircraft approaching their arrival
airport is an
important air traffic management task performed by air traffic control. It is
important to
deliver an arriving aircraft to an arrival meter fix within an allowance
parameter around a
STA, despite interference from weather effects and other air traffic. In
modern air traffic,
a single airplane missing its STA will have downstream air traffic
consequences, possibly
including missing landing slots.
[0*04] An accurate four dimensional trajectory (4DT) in space (latitude,
longitude,
altitude) and time enables air traffic control to evaluate air traffic and the
future location
of an aircraft. These parameters can also be used by air traffic control for
schedule
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management purposes to absorb an air traffic delay and change the arrival time
of
downstream air traffic by longitudinal (speed changes), lateral (flight path
lengthening or
shortening), or vertical (lowering the cruise altitude to reduce speed)
alterations.
Currently, a combination of speed changes and lateral alterations in flight
paths is used to
absorb time delays.
100051 As used herein, trajectory is a time-ordered sequence of three-
dimensional
positions an aircraft follows from take-off to landing, and can be described
mathematically, in contrast, a flight plan is a series of documents that are
filed by pilots
or a flight dispatcher with a civil aviation authority that includes such
information, such
as departure and arrival locations and times, that can be used by air traffic
control (ATC)
to provide tracking and routing services. Trajectory is a means of fulfilling
an intended
flight plan, with uncertainties in time and position.
100061 Trajectory Based Operations (TBO) is an important component of
advanced
air traffic systems to be implemented sometime in the near future, including
the US Next
Generation Air Transport System (NextGen) and the European Single European Sky
ATM Research (SESAR). TBO concepts provide the basis for improved airspace
operation efficiency. Trajectory synchronization and negotiation implemented
in TBO
also enable airspace users (including flight operators, flight dispatchers,
flight deck
personnel, Unmanned Aerial Systems, and military users) to regularly fly
trajectories
closer to their preferred trajectories, enabling business objectives,
including fuel and time
efficiency, wind-optimal routing, and weather-related trajectory changes, to
be
incorporated into TBO concepts. As a result, significant research has gone
into
developing the system framework and technologies to enable TBO.
[0007] An overarching goal of TBO is to reduce uncertainty associated with
the
prediction of an aircraft's future location through the use of the
aforementioned 4DT in
space and time. The precise use of 4DT dramatically reduces uncertainty in
determining
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an aircraft's current and future position and trajectory relative to time, and
includes the
ability to predict when an aircraft will reach an arrival meter fix (a
geographic location
also referred to as a metering fix, arrival fix, or comerpost) as the aircraft
approaches its
arrival airport. Currently, air traffic control relies on "clearance-based
control" systems,
which depends on observations of an aircraft's current location, typically
without much
further knowledge of the aircraft's trajectory. Typically, this results in the
aircraft flying
a route that is determined by air traffic control and which is not the
aircraft's preferred
trajectory. Switching to TBO would allow an aircraft to fly along a user-
preferred
trajectory.
100081 In TBO,
user preferences determine the choices made in air traffic operations.
More specifically, aircraft trajectories and operational procedures are a
direct result of the
business objectives of the aircraft operator. A fundamental element of these
business
objectives is the Cost Index, (CI) which is the ratio of time costs (costs per
minute) to
fuel costs (cost per kg) of an aircraft in flight. The CI of an aircraft
determines its
optimal flight speed and trajectory, and is a function of atmospheric
conditions, aircraft
performance capabilities and trajectory, and as a result is nearly unique to
every flight. In
addition, factors such as speed and altitude do not necessarily increase
linearly with
increasing Cl. As such, the computation of Cl in ground simulation is
difficult.
100091 Currently,
air traffic controllers maintain traffic patterns with the first concern
being safety and separation between aircrafts. Such patterns are made with no
concern
for preferred aircraft trajectories, and as such no efforts are made by air
traffic controllers
to conserve costs for the aircraft operators. It has been observed that in
instances such as
this, other viable trajectory changes may be made which are much more cost
effective.
The optimization and computation required to determine a preferable trajectory
would
most likely not be possible by a human operator or traffic controller, and
would need to
be provided by a computer system. In such a case, a computer would provide
preferable
trajectory options to a human operator, who would then choose from a series of
possible
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trajectories.
100101 For TBO to function effectively, it requires accumulation and
compilation of
trajectory data from all relevant aircraft. User-preferred trajectories, those
which are
most desirable by the aircraft operators, may often conflict with one another,
especially in
air traffic systems which are no longer-clearance based. Although TBO will
improve
efficiency, it must deal with trajectory and traffic conflicts. Trajectory
negotiation
determines the trajectory requirements or intentions of a variety of aircraft,
and attempts
to form a solution which meets as many user preferences as possible and make
the best
use of available airspace. Such a trajectory negotiation relies on aircraft
trajectory data as
well as human decision-making and trajectory preferences.
100111 Currently, lateral changes to a flight path, as well as speed
changes, are used
to absorb air traffic flight delays. However, it would be desirable if early-
descent
trajectory changes could be used to absorb flight delays in air traffic. The
National
Aeronautics and Space Administration's (NASA) Ames Research Center has
researched
the feasibility of using altitude change (descent) advisory capability in
NASA's En-Route
Descent Advisor (EDA) by conducting human-in-the-loop simulation experiments
with
experienced Air Route Traffic Control Center (ARTCC) sector controllers, as
reported in
a paper published at the AIAA Guidance, Navigation, and Control Conference,
entitled
"Impacts on Intermediate Cruise-Altitude Advisory for Conflict-Free Continuous-
Descent Arrival," August 8-11, 2011, Portland, Oregon USA.
100121 In a continuous-descent or early-descent trajectory, an aircraft
begins
descending at an idle or near-idle thrust setting much earlier than in a
standard trajectory.
By beginning a slow descent much earlier in a flight path, a time delay may be
absorbed,
and less fuel may be exhausted. The basic outline of an early-descent
trajectory is shown
in FM. 1. An aircraft following an early-descent trajectory may either
continuously
descend to an appointed meter-fix location, or descend to an intermediate
lower altitude,
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allowing it to fly at a slower speed to absorb a flight delay and potentially
consume less
fuel.
100131 When a time delay in air traffic must be absorbed, early-descent
maneuvers
may provide a distinct cost advantage over lateral or speed changes to an
aircraft's
trajectory. However, determining preferable trajectories that meet air traffic
safety
constraints, absorb proper delay and conserve filet is most likely beyond the
computational capabilities of human controllers, especially if the human
controllers are
preoccupied with preventing air traffic conflicts. Therefore, a system must be
in place
which is capable of determining a preferable trajectory, or several preferable
trajectories,
which may include an early-descent maneuver, and then capable of providing
these
trajectories to a human controller who can relay the command on to the
aircraft pilots. In
the event that an air traffic conflict necessitates an aircraft maneuver to
absorb a time
delay, this system would provide trajectory options preferable to a simple
lateral or
longitudinal change in aircraft trajectory, while still being conscious of the
air traffic
safety and operational constraints due to surrounding traffic.
(0014I U.S. Patent Application Publication No. 2009S0157288 attempts to
solve a
similar problem, but limits the actors in the solution to individual aircraft.
An aircraft
receives only a time delay factor from air traffic control and, in isolation
from any
additional information from ground systems, determines the best trajectory
modification
to meet this time delay.
[0015] While information and decision-making can be left entirely to either
an
aircraft or ground systems, there are limitations to the accuracy and
availability of
information in either of these approaches. Typically, such calculations are
contingent on
the entirety of air traffic conditions in the vicinity of the aircraft, and
therefore the results
of such decision making are not isolated to the aircraft.
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BRIEF DESCRIPTION OF THE INVENTION
[00161 The present invention provides methods and systems for managing the
time
schedule for arriving aircraft approaching their arrival airport. The
invention provides
means for altering aircraft flight trajectories including, but not limited to,
early cruise
descents, in order to compensate for air traffic scheduling changes including,
but not
limited to, time delays resulting from one or more aircrafts missing its/their
STA
(scheduled time of arrival).
(0017) According to a first aspect of the invention, a schedule management
system is
provided for managing air traffic comprising multiple aircraft that are within
a defined
airspace and approaching an arrival airport, with each of the multiple
aircraft having
existing trajectory parameters comprising three-dimensional position and
velocity. The
schedule management system includes on-aircraft flight management systems
(FMSs)
individually associated with the multiple aircraft and adapted to determine
aircraft
trajectory and flight-specific cost data of the aircraft associated therewith,
and an air
traffic control system that is adapted to monitor the multiple aircraft but is
not located on
any of the multiple aircraft. The air traffic control system has a decision
support tool and
is operable to acquire the aircraft trajectory and the flight-specific cost
data from the FMS
and generate a STA for each of the multiple aircraft for at least one location
(for example,
a meter fix point) along an approach to the arrival airport. If any of the
multiple aircraft
miss the STA thereof at the location and thereby delays a second of the
multiple aircraft
flying towards the location to impose a later STA for the second aircraft, the
air traffic
control system is operable to transmit the aircraft trajectory and the flight-
specific cost
data to the decision support tool, utilize the decision support tool to
determine if a
particular trajectory alteration is more cost-efficient for the second
aircraft to absorb the
delay associated with the later STA, and then transmit instructions to the
second aircraft
based on a human decision facilitated by the decision support tool.
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100181 According to a second aspect of the invention, a method is provided
for
managing air traffic comprising multiple aircraft that are within a defined
airspace and
approaching an arrival airport, with each of the multiple aircraft having
existing
trajectory parameters comprising three-dimensional position and velocity. The
method
includes determining aircraft trajectory and flight-specific cost data of each
of the
multiple aircraft with on-aircraft FMS individually associated with the
multiple aircraft,
monitoring the multiple aircraft with an air traffic control system that is
not located on
any of the multiple aircraft, and then generating with the air traffic control
system a STA
for each of the multiple aircraft for at least one location (for example, a
meter fix point)
along an approach to the arrival airport. If any of the multiple aircraft miss
the STA
thereof at the location and thereby delays a second of the multiple aircraft
flying towards
the location to impose a later STA for the second aircraft, then the method
further
comprises transmitting the aircraft trajectory and the flight-specific cost
data acquired
from the FMSs to a decision support tool of the air traffic control system,
utilizing the
decision support tool to determine if a particular trajectory alteration is
more cost-
efficient for the second aircraft to absorb the delay associated with the
later STA, and
then transmitting instructions to the second aircraft based on a human
decision facilitated
by the decision support tool.
[00191 A technical effect of the invention is that, while prior approaches
to managing
time schedules for arriving aircraft have relied on information and decision-
making that
are left entirely to either the individual aircraft or a ground system, the
present invention
seeks to provide an accurate and comprehensive schedule management system that
uses
aircraft and flight data received from aircraft within the sphere of influence
of a ground-
based air traffic control system, for example, an air traffic control center,
and then uses
decision support tools (DST) of the ground system to compute the estimated
time of
arrival (ETA) for each aircraft being managed and determine whether there is a
requirement to absorb a time delay or temporally advance an aircraft.
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[00201 Other aspects and advantages of this invention will be better
appreciated from
the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
100211 FIG. 1 schematically represents a basic outline of early-descent
trajectories
that can be implemented by embodiments of the present invention.
100221 FIG. 2 is a block diagram of a schedule management method and system
for
managing air traffic approaching an arrival airport on the basis of the
trajectories and
flight-specific cost data of the individual aircraft.
100231 FIG. 3 is a graph that represents a relationship between a given
time delay and
altitude changes that can be employed to absorb the time delay from a certain
distance to
a meter-fix point in an early-descent maneuver.
[00241 FIG. 4 represents that potential cost advantages may be achieved
when
absorbing a time delay in air traffic through the implementation of early-
descent
maneuvers to an aircraft's trajectory as compared to conventional lateral or
speed
changes.
DETAILED DESCRIPTION OF THE INVENTION
100251 The present invention provides a schedule management system and
method
for managing air traffic approaching an arrival airport. According to a
preferred aspect of
the invention, aircraft within the airspace are equipped with on-aircraft
flight
management systems (FMSs) that determine aircraft trajectory and flight-
specific cost
data of the individual aircraft on which they are installed. The schedule
management
system receives the aircraft trajectory and flight-specific cost data from the
FMSs of the
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aircraft within the sphere of influence of an air traffic control (ATC) center
whose ground
system is equipped with a decision support tool (DST). The air traffic control
system
determines the scheduled time-of-arrival (STA) for the aircraft at one or more
meter fix
points along one or more approaches to the arrival airport and, if any
aircraft misses its
STA and thereby imposes a time delay on one or more other aircraft flying
towards the
meter fix point, the DST utilizes the aircraft trajectory and flight-specific
cost data of the
other (delayed) aircraft to determine if aircraft trajectories changes would
be
advantageous in absorbing the time delay(s). If appropriate, such a
determination can be
transmitted to the delayed aircraft by air traffic control personnel.
(00261 According to a preferred aspect of the invention, flight-specific
cost
information is generated by aircraft and provided to the DST for analysis.
Based on
existing computational capabilities, the DST is preferably part of a ground-
based
computer system and not on an aircraft. This provides larger data storage and
processing
capabilities, given that the DST can be of a much larger size, designed to fit
in a room or
building and not in an aircraft cabin. The ground-based DST also provides a
better
medium for compiling incoming data from multiple aircraft under the control of
an air
traffic control system. It should be noted that this embodiment of the
invention offers the
capability of facilitating advances in air traffic control, in particular, to
accommodate
advanced air traffic systems such as l'rajectory Based Operations (TBO) to be
implemented in the future, including the NextGen and SESAR evolutions. As
such, the
DST is designed to work not just with one aircraft, but with a large number of
different
aircraft, trajectories, positions, and time constraints.
100271 An arrival manager (AMAN) is commonly used in congested airspace to
compute an arrival schedule for aircraft at a particular airport. The computer
system of
the schedule management system can use aircraft surveillance data and/or a
predicted
trajectory from the aircraft to construct a schedule for aircraft arriving at
a point, typically
a metering fix located at the terminal airspace boundary. Today, this function
is
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performed by the FAA's Traffic Management Advisor (TMA) in the USA, while
other
AMANs are used internationally. In general, this invention can make use of an
arrival
scheduler tool that monitors the aircraft based on aircraft data and computes
the
sequences and STAs of arriving aircraft to the metering fix. Although most
current
schedulers compute STAs using a first-come first-served algorithm, there are
many
different alternative schedule means, including a best-equipped best-served
type of
schedule. On the other hand, the DST is an advisory tool used to generate the
alternative
trajectories that will enable a later-arriving aircraft to accurately perform
an early-descent
trajectory (which may result in reduced speed) that will deliver the aircraft
to the
metering fix according to the delayed STA computed by the computer system for
the
later-arriving aircraft.
100281 As a
nonlimiting example of an implementation and operation of a schedule
management system of this invention, FIG. 2 represents an air traffic conflict
that has
arisen in the vicinity of an airport, in which two aircraft will reach the
traffic pattern of
the airport at the same time. In the scenario to be described in reference to
FIG. 2, one
aircraft (depicted in FIG. 2) must be delayed so that the other aircraft (not
shown) can
enter the traffic pattern first and an adequate amount of space will be
provided between
the aircraft. Though an air traffic controller could simply request that the
delayed aircraft
reduce its cruise speed or make another simple trajectory change, doing so may
not be the
most cost-effective or desirable solution for the aircraft operator. Within
the schedule
management system, the air traffic control system is provided with a ground-
based
computer system that monitors the 4D (altitude, lateral route, and time)
trajectory (4DT)
of each aircraft as it enters the airspace being monitored by the air traffic
control system.
The aircraft, appropriately equipped with an on-board FMS (or, for example, a
Data
Communication (DataComm) system) are capable of providing this information
directly
to the computer system. In particular, many advanced FMSs are able to
accurately
compute 4DT data, which can be exchanged with the computer system using CPDLC,
ADS-C, or another data communications mechanism between the aircraft and air
traffic
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control system, or another digital exchange from a flight dispatcher.
100291 For each aircraft within the monitored airspace, the computer system
associated with the air traffic control system computes an estimated time of
arrival (ETA)
for at least one metering fix associated with the arrival (destination)
airport shared by the
aircraft. ETAs for multiple aircraft are stored in a queue that is part of a
data storage unit
that can be accessed by the computer system and its DST. In the scenario
described in
reference to FIG. 2 in which a first aircraft (not shown) enters the traffic
pattern first
resulting in the delay of another aircraft (depicted in FIG. 2), the computer
system
performs a computation to determine, based on information inferred or
downlinked from
the aircraft, the ETA of the first aircraft and an appropriate delay time for
the delayed
aircraft.
100301 With the use of the 4DT, flight-specific cost data, and optionally
preferences
based on business objectives of the aircraft operator acquired from the
delayed aircraft,
the computer system utilizes the DST to compute several possible alternative
trajectories
which would adequately delay the delayed aircraft and resolve the traffic
conflict while
also conserving aircraft operating costs by potentially initiating an early
descent. In this
case, through the use of an appropriate ATCo interface (such as a graphic/user
interface),
an air traffic controller can choose one of the possible trajectories,
potentially including
an early descent, recommended by the DST and relay this request to the delayed
aircraft.
As such, a human can still make the decision to change the trajectory of the
aircraft, but
the DST facilitates better operational efficiency by computing and
recommending more
cost-effective solutions that may include one or more early-descent
trajectories. Once the
descent trajectory request has been noted ("Pilot Check") and implemented
("4DT") by
the delayed aircraft, the air traffic control system can continue to monitor
the trajectory of
the aircraft for conformance to the request. If necessary and possible, the
air traffic
control system may update the ETAs to the meter fix for each aircraft stored
in the queue
of the data storage.
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100311 As indicated in FIG. 2, the schedule management system can be
implemented
to work in reference to initial and final scheduling horizons. The initial
scheduling
horizon is a spatial horizon, which is the position at which each aircraft
enters the given
airspace, for example, the airspace within about 200 nautical miles (370.4 km)
of the
arrival airport. The ATM system monitors the positions of aircraft and is
triggered once
an aircraft enters the initial scheduling horizon. The final scheduling
horizon, also
referred to as the STA freeze horizon, is defined by a specific time-to-
arriving metering
fix. The STA freeze horizon may be defined as an aircraft's metering fix ETA
of less
than or equal to, for example, twenty minutes in the future. Once an aircraft
has
penetrated the STA freeze horizon, its STA remains unchanged, the schedule
management system is triggered, and any meet-time maneuver is uplinked to the
aircraft
to carry out one of the alternative trajectories devised by the DST of the
schedule
management system.
100321 The basic outline of an early-descent trajectory for the delayed
aircraft is
schematically represented in FIG. I, which evidences that the aircraft begins
descending
(for example, at an idle or near-idle thrust setting) much earlier than in a
standard
trajectory. By beginning a slow descent much earlier in a flight path, a time
delay is
absorbed and, in preferred embodiments, less fuel is exhausted. The aircraft
may either
continuously descend to an appointed meter-fix location or descend to an
intermediate
lower altitude, allowing it to fly at a slower speed to absorb a flight delay
and consume
less fuel.
100331 When a time delay in air traffic must be absorbed, early-descent
maneuvers of
the type represented in FIG. I and made possible by the schedule management
system of
FIG. 2 can provide a distinct cost advantage over lateral or speed changes to
an aircraft's
trajectory. Experimental evaluations leading up to the present invention
included
simulations of multiple Boeing 737 model aircraft types, wind profiles, and
meet-time
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256525A
goals, including simulations that generated the time-delay data graphed in
FIG. 3 as well
as predicted fuel cost plotted in FIG. 4. The graph in FIG. 3 represents a
relationship
between how much altitude change was required to absorb a certain time delay
given a
certain distance from a meter-fix point in an early-descent maneuver. While
fuel use is
generally higher for early cruise descents than for corresponding path
stretches in
constant wind conditions, the presence of non-constant wind fields was viewed
as
potentially providing significant fuel savings compared to a path stretch at a
higher
altitude. Also developed was a cost coefficients-based framework that can
support a
ground-based computation of an optimal meet-time schedule management maneuver.
A
discussion of such a framework is discussed in Torres et al., "Trajectory
Management
Driven by User Preferences," 30th Digital Avionics Systems Conference (October
16-20,
2011).
[0034] The cost of operating a flight may be decomposed into the cost of
fuel and
other direct and time related costs, including, but not limited to, crew pay,
aircraft
maintenance, passenger and cargo logistics, and equipment devaluation.
Preferred
embodiments of the invention involve the extraction of the effective operating
cost from
the on-board FMSs of aircraft. A suitable mechanism for calculating and
evaluating
operating cost may include the Cost Index, as discussed above and in Torres.
Such
calculations and evaluations for a specific aircraft would likely be located
on the aircraft
itself since the hardware requirements necessary for data storage and
processing would be
far less than required for the DST of the ground-based system. The information
to be
processed would be contingent on or directly relevant to a specific aircraft
as opposed to
generally pertaining to all aircraft within the air traffic being monitored by
a given air
traffic control center. The mechanism would then make that information
available
(down-linked) to the air traffic control system and its DST.
[0035] As noted above, Torres contains a discussion of a cost coefficients-
based
framework that can support a ground-based computation of an optimal meet-time
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schedule management maneuver, by which a new cost-optimized STA for an
aircraft can
be determined in response to an earlier aircraft missing its STA. Generally,
such a
framework involves an aircraft computing the cost (either relative to the
current planned
trajectory or an absolute cost) for various types of changes to its current
planned
trajectory, in terms of speed, lateral path change (increase in path length),
or a change in
cruise altitude. The cruise altitude change would most likely be a decrease in
cruise
altitude to reduce speed, though potentially an increase in cruise altitude
may be
appropriate, for example, if a stronger headwind at a higher altitude may
result in an
overall time delay capable of meeting a later STA for the aircraft
necessitated by an
earlier aircraft missing its STA. This cost information is transmitted to a
DST on the
ground (potentially as a set of cost coefficients from the aircraft).
(00361 In view of the above, the cost information can be used to determine
if a
particular course alteration would be a more efficient method of meeting a
time schedule
than, for example, a path stretch or another maneuver. A nonlimiting example
of such a
course alteration would be an early-descent trajectory that is optimal for
meeting a new
STA for an aircraft, a particular example being a later STA necessitated by an
earlier
aircraft missing its STA. The DST would compile available information provided
by the
aircraft into a more useful tool. If part of TBO described earlier, the DST
generates and
compiles the information by which trajectory negotiation can take place, and
from which
the DST preferably generates several possible alternative trajectories, one or
more of
which may be preferred by the aircraft operator and/or fit into the
constraints of the
existing air traffic environment. The intention is that the DST is able to
facilitate better
use of airspace and meet aircraft user-preferred trajectories by providing all
the available
flight data, as well as preferred trajectories, to one or more human users
through an
appropriate interface that allows the users to make decisions based on the
trajectories and
potentially additional information.
[00361 With access to the STA of the aircraft being managed, the DST can
compute,
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based on the predicted aircraft trajectory, the ETA for the aircraft. If the
ETA of the
aircraft is sooner than its STA, there is a requirement to absorb time delay.
Conversely, if
the ETA of the aircraft is later than its STA, there is a need to temporally
advance the
aircraft. The ground-based DST may consider various combinations of speed
changes
(either a single speed instruction or as a time constraint, such as a Required
Time of
Arrival (RTA)), lateral path stretch or shortcut, and/or cruise altitude
change. The cost
surfaces constructed from the down-linked cost coefficients are utilized to
evaluate and
select a meet-time maneuver for the aircraft, and more preferably the best
meet-time
maneuver that appears to be most advantageous for the aircraft while meeting
the STA at
the arrival meter fix.
100371 In view of
the above, the present invention enables an early cruise descent as
part of the feasible options set available to an air traffic controller,
broadening the options
set for meet-time schedule management. This increases the available degrees of
freedom
as well beyond speed changes and path stretches, allowing better
identification of
conflict-free trajectories that meet timing requirements in congested
airspaces. With a
broader options set, and a means to compute costs associated with each option,
aircraft
business objectives may be considered and satisfied.
[0038j While the
invention has been described in terms of certain embodiments, it is
apparent that other forms could be adopted by one skilled in the art.
Accordingly, it
should be understood that the invention is not limited to the specific
embodiments
described herein. Therefore, the scope of the invention is to be limited only
by the
following claims.
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