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S ystemsAnalysis LaboratoryHelsinki University of Technology

A Simulation Model for Aircraft Maintenance in an Uncertain Operational Environment

Ville Mattila, Kai Virtanen and Tuomas Raivio

Systems Analysis LaboratoryHelsinki University of Technology

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S ystemsAnalysis LaboratoryHelsinki University of Technology

Objective

• Simulation of flight and maintenance operations of the aircraft fleet of the Finnish Air Force (FiAF)

• Importance for maintenance designers– Predicting supportability requirements

– Evaluating performance of operating policies

• Special interest in operations of crisis situations– Uncertainty due to limited knowledge of such

circumstances

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S ystemsAnalysis LaboratoryHelsinki University of Technology

Flight and maintenance operations• A complex logistic system

– Overall performance greatly influences the fleet’s operational capability

Flight policy

Periodic maintenance

Failure and damagerepairs

Equipment reliability

Personnelresources

Supply of materials

Operatingconditions

Crisis situations

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S ystemsAnalysis LaboratoryHelsinki University of Technology

Operational environment

• The fleet operates under a threat of an enemy

– Limited knowledge of actual encounters

Uncertainty of operating conditions

Uncertainty of model parameters and model form

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S ystemsAnalysis LaboratoryHelsinki University of Technology

Flight operations in crisis situations

• Increased and uneven flight intensity– Reacting to enemy’s actions

• Engagements– Battle damages

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S ystemsAnalysis LaboratoryHelsinki University of Technology

Maintenance operations in crisis situations

• Changed maintenance requirements– Emphasis on battle damage repairs

– Varying intensity

• Decentralization of airbases– Maintenance facilities threatened by

the enemy

• Specialized maintenance personnel

• Uncertain supply of materials

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S ystemsAnalysis LaboratoryHelsinki University of Technology

Uncertainty in model construction

• Construction based on incomplete information

– Emphasis of expert knowledge

– Experience of normal operations

– Live exercises and contingency plans

• Ambiguity in defining the model

User is allowed the flexibility to describe a variety of operating policies and conditions

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S ystemsAnalysis LaboratoryHelsinki University of Technology

The simulation model

• Discrete-event approach

• Features– 3 squadrons operating

from own airbases

– Central depot-level maintenance facility

– Periodic maintenance, failure, and damage repairs

– Personnel and material resources

• Implemented with Arena-software

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S ystemsAnalysis LaboratoryHelsinki University of Technology

Structure of the model

Class I airbase

Class II airbases, up to 3

Mission

Failures

Damages

Need forperiodic

maintenance?

D-level maintenance Fuel and materials supply

Destroyedaircraft

3 Squadrons

Everyday maintenance

I- level maintenance

O-level maintenance Wait

Everyday maintenance

Damage repair

O-level maintenanceWait

Mission generation

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S ystemsAnalysis LaboratoryHelsinki University of Technology

Model validation

• Evaluation by subject matter experts– Assumptions, results

– Various groups of FiAF personnel

– In different phases of the modeling effort

• Comparison of results– To reference data from normal operations

– To results of an earlier tentative simulation study

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S ystemsAnalysis LaboratoryHelsinki University of Technology

Example analysis

• Changing maintenance policy during a crisis– Periodic maintenance is discarded to release

resources to other activities

– How does the change affect aircraft availability?

• A scenario with 4 phases1 Increased flight intensity

2 Further increase in the amount of flights, decentralization of airbases

3 Aerial battles

4 Decreased flight intensity due to losses

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S ystemsAnalysis LaboratoryHelsinki University of Technology

Results

• Change in policy is necessary to sustain operational capability

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0.2

0.4

0.6

0.8

1

0 50 100 150 200 250

Time (days)

Av

aila

bili

ty

In 1st phase In 2nd phase

In 3rd phase Not employedEmployment of new policy

1. 2. 3. 4.

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S ystemsAnalysis LaboratoryHelsinki University of Technology

Conclusions

• A model for fleet operations in an uncertain operational environment– Quantitative assessment of maintenance

policies in crisis situations

• Implementation with a graphical simulation software– Easily manageable simulation analyses for

maintenance designers

– A tool for training of maintenance personnel