As mentioned in the article of Rolling-Wave Planning, the cost estimate at this stage will be a class 5 estimate as defined by the AACE Recommended Practice 104R-19. This estimate usually has an accuracy range of minus 50% to plus 100%. The schedule duration calculated for the project will follow the same steps. The definition of the project duration at this stage is based most of the time on benchmarking. However, unlike the cost estimate, it is not the best way to calculate the total cycle time or the execution duration of the project. Project drivers, execution constraints, and project risks are better in making a duration prediction. The planner/schedule will put these factors together on a simple one-page Gantt chart to study their impact on each other and develop a Level-1 schedule that corresponds to Class 5 estimate. These factors will be covered in the following paragraphs then examples of Level 1 schedules will be shown.

Project Drivers

Project drivers are those factors that motivate and guide the development of a project during its lifetime. They can be internal, such as financial constraints, deadlines, customer and supplier expectations, or external, like market trends, legal and regulatory requirements, labor and materials costs etc. These drivers are combined to define the scope of the project. Industrial projects have many drivers mainly defined by the market, the maintainability of the plant, and the protection of the environment. The latter is mostly defined by governmental regulations or the desire of the owner company to contribute positively to the quality of the environment.

High-level scope-breakdown (WBS)

A Work Breakdown Structure (WBS) is an approach used to divide an industrial project into smaller, more manageable components. It is typically hierarchical in nature, showing the overall project at the top level, with subsequent levels representing further divisions of the project. The WBS helps identify all of the individual components and tasks that need to be completed for the successful completion of the project. When reaching to the smallest manageable component, it is possible to start adding tasks that reflect the execution strategy of those components. Each component is assigned a unique identifier to aid in planning tasks and resources, and to ensure that all tasks have been considered in the planning phase. A WBS is also used to assign responsibility and accountability, plan project duration and schedule, and to estimate project costs.

During the early planning phase, namely the first stage of front end planning (FEP-1), the high level WBS only is needed. Below, there is an example for high level WBS for an industrial boiler used for power generation.

The Conceptual Schedule

The plan or the schedule will be built as follows:

• The total duration of the project will be calculated in a similar manner like the estimate based on benchmarking the project to completed projects with similar production capacity. The execution duration will be also calculated the same way.

• The schedule of the FEP-1 Phase which is usually a few procedural steps to complete FEP-1 will be a detailed Level 3 schedule. This schedule usually fits in one or two pages.

• The schedule for FEP-2 will be a top-down Level 2 schedule to show some details of the work to be performed during the FEP-2 Phase.

• The schedule for FEP-3, Execution, and Startup Phases will be a Level 1 schedules to show the main milestones, key scope breakdown areas,

• Project constraints can be shown in a separate section or made clear in their subsequent area. Examples of project constraints are the permits, availability of resources, equipment tie-ins, very long lead items, etc.

This schedule is not a detailed critical path schedule. It should be treated as a planning tool to indicate the initial criticality of major construction areas, the impact of potential risks that might happen during the project execution, and how to react to project constraints. The figure below shows the one-pager schedule for the boiler project. The schedule is grouped by the WBS mentioned above. The general area contains milestones, FEP-2, FEP-3, and the clearly defined constrains. The rest of the schedule is displaying the engineering, procurement, and fabrication (or construction) of each of the scope areas.

Looking at this schedule, it can be found that the "Environmental Permit" is not the only constraint. Yes, it represents a constrain on the startup of the boiler especially with the unknowns associated with it. However, the "Furnaces" area requires longer engineering and longer construction than other areas. Also, the "Control Room" procurement is very long with risks of delivery on time. This very long lead item represents another constraint on the project.

The project management team (PMT) should work on understanding the factors impacting the date of boiler startup and work on minimizing the risk of overruns. For example, the "Control Room" procurement can be placed and awarded to the selected vendor during the FEP-3 stage. Another example is accelerating the engineering required to order the "Environmental Permit". For the "Furnace" area, it needs to have a very high priority by the engineering and fabrication teams. Engineering and construction can be carefully overlapped for this area to minimize the risks of extending its duration which would impact the mechanical completion date.

In conclusion, the initial or conceptual schedule needs to describe the:

• Scope

• Constraints

• Execution Strategy

The benefit of the conceptual schedule is to plan the timing and priorities for the execution phase. It is not a real critical path schedule. It is a planning tool that reflects the reality of the project. The promise date produced by this conceptual schedule is more realistic than a date driven by benchmarking only. This approach incapsulates the reality of the project, its drivers, and constraints into the calculation of the promise date. Benchmarking is needed to start but it is not enough to conclude a completion date of a project.