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Capacity Metric |
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In current ATM systems capacity is associated with air traffic controller’s workload.
A number of methods and techniques for assessing this workload have been developed and are used in real-time simulations to assess the effects on controller workload when new concepts or controller tools are being introduced. However limitations to this approach have been identified when considering simulations of advanced ATM systems. Such systems are those where degrees of automation are introduced, such as controller assistance tools, and elements of the control task are shared between the system “actors” (humans - Controllers, Pilots, etc. and machine processes). These limitations stem from the following:
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- It is no longer evident that controller workload will be the limiting factor when considering capacity - other system elements may limit performance of the system before the controller becomes overloaded
- Controller tasks and activities will be different and therefore workload assessments will be influenced by levels of training and/or trust in the system.
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The second element is especially important in the context of real time simulations as the nature of simulations is such that it will not be possible to train controllers to a sufficient degree to become fully confident with and trust a new system and therefore any workload assessment will be influenced by these factors.
INTEGRA has developed a capacity metric to accommodate these limitations. The metric assesses what load (termed Information Processing Load in INTEGRA) is required by each actor (Human or machine) and compares this load with the maximum load acceptable for that actor.
To evaluate the INTEGRA Capacity metric the concepts of Actors and "Information Processing Load" (IPL) have been introduced.
Actors can be any entity that performs an operation within the system, they can be human, systems or parts of systems. For example, a Tactical Controller, a Trajectory Predictor or a Conflict Probe.
The INTEGRA Capacity metric is based on the following premises:
- There are a number of actors identifiable that perform tasks in an ATM system e.g.:
Tactical Controller
Planning Controller
Conflict probe
etc.
- Information has to be processed to execute an ATM task e.g.:
Monitor traffic
Detect a conflict
Resolve a conflict
etc.
- Task execution is determined from events detected in the system and is allocated according to the determined “difficulty” of the task, e.g. the difficulty of the conflict resolution.
- Each actor will have a different maximum limit as to the amount of information that can be handled.
- Capacity of the system is reached when any one of the actors is overloaded.
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Principles of the Capacity Metric |
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The actors, both human and system, required for the Capacity metric are identified by examining the operational concept or operational procedures for the system.
The various activities that need to be carried out to meet the operational requirements are identified. These activities are then allocated to the actor responsible for carrying them out.
The simulation is run and the simulation events recorded.
The Capacity algorithm operates with simulation output data, such as trajectory data or recorded operator inputs, to identify an amount of Information Processing Load for each of the activities.
The IPL is calculated using the simulation output data and allocated to the responsible actor at the time an activity occurs. The IPL for each actor is summed and compared with a "threshold" to determine whether the actor was overloaded at any time. The threshold is determined by evaluating the IPL scores over several simulation exercises.
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| Click here to view the steps in applying the Capacity Metric |
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The INTEGRA Capacity Metric is documented in the following:
| Detailed Specification of Capacity Inputs - Processing - Outputs
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| Detailed Specification of Capacity Metric Analysis Software
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| Capacity Metric User Guide
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Last validation: 15/03/2007
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