DIRECT-TO TOOL FOR EN ROUTE CONTROLLERS

H. Erzberger, B. D. McNally, M. Foster, D. Chiu, and P. Stassart



Abstract

In recent years, advances in air traffic control have often been
evaluated by how effectively they further the goals of "free flight."
Although the notion of free flight is difficult to define precisely, any
method that reduces constraints and increases the freedom of airspace
users to operate aircraft in a manner they consider optimum is
considered to be a step toward free flight. Since the notion became
popular a number of years ago, numerous innovations, technologies and
automation methods have been investigated under the umbrella of free
flight. Some of these were recommended for national development by a
consensus of airspace users, operators and air traffic control experts [1]. 
In response to these recommendations, the Federal Aviation
Administration established the Free Flight Project Office to lead and
execute the deployment effort. That effort is now well under way for the
initial (Phase 1) free flight technologies.

This paper describes the design of a new automation tool for en route
controllers, called the Direct-To Tool, that advances the goals of free
flight in the climb-to-cruise and en route segments of flight. It also
provides a compatible extension of the Free Flight Phase 1 technologies.

The insight that led to the design of the Tool originated with
experience gained in evaluating the Conflict Probe/Trial Planner (CPTP)
built into the Center TRACON Automation Systems (CTAS). During the field
test of CPTP at the Denver Center in the Fall of 1997, controllers would
usually attempt to resolve conflicts predicted by the Probe by
trial-planning resolution trajectories that led from the conflict
aircraft's current position to a down-stream fix along the
aircraft's flight plan [2]. In about 20% of such attempts, they
succeeded in finding trajectories direct to a fix that resolved the
conflict. Thus, when this method was successful, the solution had the
additional advantage of reducing the path distance to fly to the
destination. It was a surprise finding that this strategy was so often
successful. In the Denver Center tests, only aircraft that were
"fortunate" to have been identified as being in conflict had the
potential to benefit from path shortening direct-to fix trajectories.
This finding suggested the following hypothesis: Since conflicts are
random events, there must exist a similar percentage of non-conflict
aircraft that could reduce their path distances by direct-to fix
trajectories. Armed with this knowledge, controllers at a follow-on test
of CPTP at the Fort Worth Center used the Trial Planner to manually
search for non-conflict aircraft that could benefit from direct-to fix
trajectories [3]. Through trial and error with CPTP they found many
aircraft, especially departures from DFW, that were eligible for path
shortening direct-to fix trajectories.

While effective for finding and resolving conflicts and conflict probing
direct routes for any aircraft selected by the controller, CPTP lacked
the ability to automatically identify all aircraft eligible for
direct-to routes and to determine and display the corresponding time
savings. To aircraft operators, time saving, which accounts for the
effect of winds, and not necessarily path length saving is the
appropriate measure of flight efficiency. The need to solve these
problems formed the nucleus for the requirement of the Direct-To Tool,
which is the subject of this paper.