Maintenance Forecasting and Capacity Planning Maintenance forecasting and capacity planning are two important functions for the design of an effective maintenance system.

Maintenance Forecasting It comprises the estimation and predication of the maintenance load. This maintenance load represents the driving force of the whole maintenance system.

Maintenance Load Planned maintenance works which involves all the works that are characterized by their ability to be planned and scheduled. Unplanned maintenance works which involves all works that are very difficult to be planned and scheduled. (These works depend primarily on the failure pattern and they are a major source of uncertainty in the planning process.)

The sum of maintenance load in these two category is a random variable and it’s the major factor in determining the maintenance capacity.

Capacity Planning Involves the determination of the maintenance resources that are needed to meet the maintenance load in order to achieve the organizational objectives such as: 1. Availability. 2. Reliability. 3. Quality rates. 4. Delivery dates.

The Essential Element of the Capacity Planning is the determination of : Skills of craftsmen. The exact number of various type of craftsmen. Types of maintenance equipment and tools The exact number of maintenance equipment and tools. Spare parts and materials. The right level of backlog. Overtime capacity. Contract maintenance.

Forecasting Model The considerations used to select the forecasting technique are: The purpose of the forecast. The time horizon for the forecast The availability of the data needed for particular technique.

Forecasting Model The model is judged by the following criteria: Accuracy which is measured by how accurately the model predicts future values, and is judged by the difference between the model forecasts and the actual observed values. Simplicity of calculation, data needed, and storage requirements. Flexibility which is the ability to adjust to changes in conditions.

Qualitative Forecasting Techniques These techniques are used when these is no historical data available. The way to forecast the value of an item is through relying on the estimates of experts and their judgment.

Qualitative Forecasting Techniques The role of the analyst is to : Systematically extract information from the expert by using questionnaire and interviews. Help the expert to quantify his knowledge. Identify which variables influence the forecast and the impact of each one. Reach an agreement on the magnitude of the variables by taking (the best case, expected case, and the worst case scenarios) and use them to estimate the magnitude of the variables that affect the forecast.

Quantitative Forecasting Techniques These techniques are used when the historical data is available. The models uses these techniques assume either: Future values follow historical trends. A predictor (independent) variable exists that can provide a functional relationship that predicts (dependent) the characteristic under study.

Types of Quantitative Forecasting Techniques Simple Moving Average Weighted Moving Average Regression Analysis Exponential Smoothing Seasonal Forecasting

MAINTENANCE CAPACITY PLANNING It is performed to determine the optimal level of resources required to meet the forecasted maintenance load.

Maintenance Capacity planning procedures Determine the total maintenance load. Estimate the required spare parts and material to meet the load. Determine the equipment and tools necessary for all types of maintenance work. Determine the skills and the number of workers for each skill. Provide special plans for highly computerized equipment.

Sources of Craftsmen Regular workers. Overtime in-house workers. Contract maintenance workers. The best mix is determined by using cost and availability measures.

Capacity Planning Techniques Deterministic models Stochastic models

Stochastic models Assumes the following are random variables with certain probability distributions: Forecasted maintenance load. Standard times. Other variables.

Types of stochastic techniques Queuing models. Stochastic discrete event simulation.

Deterministic models Assumes the following are fixed constants: Forecasted maintenance load. Standard times. Other variables.

Types of deterministic techniques Heuristic tableau method. Linear programming.

Heuristic Tableau Method Principles and guidelines: Maintenance work load is classified into grades according to the skill the work requires and the priority of the work. All priority work is performed by regular in-house workers as much as possible. If it is not possible to satisfy grade 1 work by regular in-house workers, use overtime.

Heuristic Tableau Method No backlog is allowed for grade 1 work. The staffing level must be determined based on the average maintenance load with a healthy backlog from grade 2 work carried out into the system. The grade 2 work can be met with overtime or contract maintenance.

Heuristic Tableau Method The overtime capacity is at most 25% of the regular in-house capacity. The maximum for backlog is 100 man-hours. If the backlog exceeds this limit, subcontracting is utilized and it is assumed that subcontracting can provide as much capacity as needed.

Heuristic Tableau Method The way to carry out The Heuristic Tableau Method: FMt = Total forecasted mechanical load. Bt-1 = Mechanical workload backlog from period t-1 TMt = Total mechanical workload for period t; TMt = FMt + Bt-1 TM i,t = Total mechanical workload of grade i in period t, i=1,2

Heuristic Tableau Method The way to carry out The Heuristic Tableau Method: RM i,t = Regular in-house capacity for mechanical workload of grade i in period t OM i,t = Overtime capacity for mechanical workload of grade i in period t CM i,t = Contract capacity for mechanical work of grade i in period t

Heuristic Tableau Method The way to carry out The Heuristic Tableau Method: Cr = Hourly cost of mechanical trade on regular time Co = Hourly cost of mechanical trade on overtime Cs = Hourly cost of subcontracting Bt = Backlog in man-hours at the beginning of period t

Heuristic Tableau Method The way to carry out The Heuristic Tableau Method: CRt = Capacity of in-house regular time in period t COt = Capacity of in-house overtime in period t CSt = Capacity of subcontracting in period t FMt = Forecasted maintenance load in period t