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particular location at a particular time
and, in return, the services and resources
needed by the airspace user will be
available” on an “on time, first served”
priority basis. The airspace user
guarantees the promised performance,
even if, for example, the winds are slightly
different to those predicted.
IFATCA says the trajectory contract
“also allows more strategic conflict
management, so that inefficient tactical
solutions do not suddenly occur”. The
trajectory contract is modified during
flight – both at the request of the airspace
user and the service provider. The number
of modifications requested would be an
indication both of the predictability of the
system and its flexibility.
In the SESAR model, most times
indicated in an operational trajectory
(commonly referred to as the Reference
Business Trajectory (RBT)) are estimates.
Some may be target times to facilitate
planning and some may be constraints to
assist, for example, queue management.
The RBT evolves during the flight and
is modified either when an automatic
The trajectory
contract is modified
during flight – both
at the request of the
airspace user and
the service provider
EUROCONTROL / IFATCA 2008: a collaborative approach to the future > Operating the network
Despite a degree of inherent scepticism, there is also guarded acceptance of the
positive potential of trajectory management – if a number of issues can be ironed out.
Anne Paylor looks at the challenges facing its introduction
Trajectory management
▼
few contract positions are required.
Whereas, in reality there may have to be
multiple trajectory points in order to
manage multiple trajectories.
Beadle also stresses that trust in the
system and confidence in the tools
provided is fundamental to controller
acceptance of trajectory management, and
he concedes this is something that will
only happen in time, through increasing
familiarity and experience.
Ultimately, though, IFATCA believes
that “the best way to address the problems
being experienced in ATM is by all
members of the ATM community
cooperating. The cooperation needed is a
serious collaboration requiring pragmatism
and compromise by all involved. It also
needs commitment to change and a will to
act at all levels including at state level.” In
essence, IFATCA believes that cooperation
and commitment to act “is more
important than the final technology or
procedures that will be implemented”.
stresses that as far as controllers are
concerned, several major issues remain to
be addressed. For example, advances in
aircraft systems have been predominantly
focused on optimising aircraft
performance on an individual flight basis.
Advances are now needed in the handling
of the interaction between the flight
trajectories of several aircraft
simultaneously. Additionally, systems still
rely too much on prediction of aircraft
position and, therefore, are affected
significantly by factors such as differences
between forecast winds and actual winds.
This can rapidly lead to uncertainty about
exactly when contracting aircraft will
arrive at specific locations, owing to the
fact that the ATM network is not a closed
system and so is subject to uncontrollable
and unpredictable events. To counteract
this, the ability of the ATM system to
respond to and mitigate uncontrollable/
unpredictable events using 4D trajectories
needs to be clearly specified in any ATM
system design.
Furthermore, the mix of 4D aircraft and
non-4D aircraft requires much more
definition within the ATM system design
rather than a simplistic expectation that
the controller will be able to resolve any
problems in a reactionary manner. Finally,
there is often a simplistic view that only a
update is triggered by specific events or
when the predicted trajectory differs from
the RBT. In either case, the amended RBT
becomes the new common reference, and
is subsequently analysed from a conflict
management and network viewpoint by
the ANSP, who will take any actions
necessary to deconflict. IFATCA is
concerned this approach does not allow
sufficient predictability or stability, leaving
the controller playing a reactionary role,
much as at present.
“There are too many variables for
prediction to be completely accurate,” says
Beadle. “We need to get away from the
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