GATEX (Airport Gate Assigment Expert System)
GATEX (Airport Gate Assigment Expert System)
Customer Swissair
Objectives Build a decision support tool for people responsible of scheduling and rescheduling of airports by using knowledge based methodology and techniques.
Development Status Developed and delivered a prototype in KEE on a TI-Explorer, during 1988

Highlighted features

1. INTRODUCTION

The goal of GATEX-project was to build a decision support tool for people responsible of scheduling and rescheduling of airports by using knowledge based methodology and techniques.
The specifications for the system have been completed by Swissair and the prototype realised by Unisys within 6 weeks in November-December 1988.

2. PROBLEM DESCRIPTION

The experts receive a list of all flights arriving and/or departing the airport the previous day. They then have to schedule -assign a suitable stand- these flights during the night. This task is complex because of the many constraints to be considered and the increasing intensity of air-traffic.
During the day many changes disturb the normal operation of an airport and the experts have to keep operations running despite of difficult weather conditions, flight delays, early arrivals, etc. To all these changes the experts have to react on an on-line basis: all consequences of any change has to be well estimated in order to avoid additional difficulties.

3. PROTOTYPE DESCRIPTION

In the following the main functionalities of this system are described.

3.1 Making initial schedule

The system first assigns closed stands and then starts scheduling the flights in following order:

  • special flights; flights requiring fixed stand, or with special destination or carrier
  • flights without handlers
    • departing flights according to category -category 1, category 2, category 3, category 4 - and within category according flight type - turnaround, transit, outbound, inbound.
    • arriving flights accordingly 
  • finally flights with handlers accordingly.

While assigning flights to stands following priorities are applied:

  • flight restrictions: single/double, dock/remote
  • best-stand and 2nd best stands for aircraft type
  • carriers to same zone
    • dock stands
    • docks without blocking other docks
    • blocking docks
  • remote stands without blocking other stands
  • blocking stands.

The first available stand in this priority list is assigned to the flight.
If no stands are available the flight is put into a not-assigned list and scheduling is continued. Flights that have not been assigned an be displayed by clicking NOT ASSIGNED button in the MAIN-MENU and further processed.

After all flights are treated a bar chart is displayed with all flight assignments.

3.2. Verifying schedule

Gatex verifies the whole schedule by checking the time buffers between 2 flights, checking that only the allowed aircraft types are assigned to the gates and/or there are no unscheduled flights.
If any conflicts are found they are listed in a window and highlighted on the bar-chart.

3.3.Solving conflicts

First all the conflicts in the schedule are collected and then rescheduling started.
While rescheduling all actions are listed in a window and collected into a slot in the knowledge base for later display.
First user has an option to change the minimum time buffer to be used.
The conflicting flights are collected:

  • type conflict: if ft is not forced to the gate it will be collected
  • time buffer conflict: this involves 2 fts -> the lower priority ft is collected if it is not forced to that stand, otherwise the other one
  • all unscheduled fts are collected.

The collected conflict fts are prioritised according to same principles as applied in initial scheduling.
For each conflicting flight the allowed stands according to aircraft type are listed. Within this list rescheduling is done the following way:

  • If there are free stands user is asked to select one or more. When more than one is selected these are assigned separately in different KEE worlds to enable later evaluation.
  • If no free stand is available then lower priority flights are removed into unscheduled fts list and current ft assigned to stand / stands selected by user in different KEE worlds.
  • If there are no lower priority fts then current ft is put into not assigned list and a message is printed on message window.
  • When all fts are treated the final schedule is shown in the bar chart.

Rescheduling may be restarted with other parameters if so desired.

3.4.Other functionalities

The user can initiate reallocations based on changes in flight arrival/departure times, aircraft types or inmatriculation, open hours of stands aircraft types allowed on stands, etc.
The timeframe and stands to be displayed can be chosen by the user according to his needs. New flights can be added and old ones deleted. The current time is shown as a thick line across the display.
Various listings can be displayed:

  • flight priority list
  • explanations of actions during rescheduling
  • initial scheduling trace.

Sample screens

Fig. 1: Display of the original schedule obtained by GATEX
Fig. 1: Display of the original schedule obtained by GATEX

Fig. 2:  Summary of actions done during rescheduling
Fig. 2:  Summary of actions done during rescheduling

Fig. 3: Menu to choose a schedule for display
Fig. 3: Menu to choose a schedule for display



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