Theme 3 - 3.3.4 - Critical Path Analysis

Question 1

What is CPA ?

Answer 1

CPA is a management tool which helps a business to identify how long a project will take and what the critical tasks in that project are

The diagrams are called network diagrams - as they show a network of tasks in a project

Question 2

What are the uses of CPA ?

Answer 2

CPA can be used to schedule a building project, for example the roof is not the first thing to go on a house and the site may not have enough space to hold all of the roof tiles at the start

A building business would therefore schedule the tiles to be delivered on like the 3rd week when they are needed - the critical task is the roof and the time its needed to be delivered - how long its going to take before we need it — how long it’s going to take to build the roof etc

CPA can also be used to:
- Launch a new product onto a market
- A photo shoot for the new product would not happen on day 1 so a schedule would be useful so bookings can be made
- Installation of new technology in a business

Question 3

What are the benefits to a business of using CPA ?

Answer 3

• Stakeholders will be able you see the total time frame for the project to be completed - this it’s important because usually the longer it takes to complete a project the more money it takes so its important for stakeholders to use CPA
• Parallel activities can be scheduled for example electricity as can work on the lighting in the kitchen while the plasterers put plaster on the upstairs walls - this will save time on the project and make sure everything is going smoothly
• this is very useful for businesses in the FMCG markets where speed is important
• useful to know when to deliver resources or arrange for labour to arrive - as you cant place down carpet while the painters are still working

Question 4

How does a CPA diagram work ?

Answer 4

• A CPA network diagram starts with a list of tasks
• It will show how long each task will take ( duration )
• It will also show what order they should be carried out in - for example to first insulate the walls before you put any thing on the external wall.

The start of the diagram is the first day of the project ( day zero ) and is shown by a circular node - the 1 on the left side of the circle indicates the node number - NOT the day

The node shows 3 things:
- on the left it shows the node number
- the top right shows the earliest day the task can start
- the bottom right shows the latest finish time that the task can end

The lines between the nodes ( circles ) , show long each task takes to be carried out - so if it says 3 then that ,means it will take 3 days

The // on a line means that is it a critical task and without it the project will fail

To find the top right figure of the node ( the earliest time that it takes to complete the task )
You just do what’s on the first line so like 3 days and then add the next line along to get the EST

Question 5

How to calculate the LFT ?

Answer 5

The LFT is the bottom right of a node and it shows the longest time that the task should take

LFT works backwards - so you take the EST and then minus the line on the left of it to find the LFT

Question 6

How can you indentify the critical path ?

Answer 6

Th longest activities are critical because those must be completed on time for the project to full complete on time - these are indicated with //

Look for the duration times and mark them on the diagram

Question 7

How to calculate the float time ?

Answer 7

When nodes are the same at the top and the bottom - there is no spare time so these tasks are critical

If these tanks are delayed they will delay the whole project a s they have to be done first and they will stop some stuff from getting done as the critical tasks hasn’t been done

So we need to know where there is some free time or ‘float’

Float = LFT - duration - EST
So the bottom right minus the middle ( line ) then minus the top right but on the other node

Question 8

What are the limitations of CPA ?

Answer 8

• All the data in the network diagram is based on estimates and can quickly become inaccurate e.g. if the weather turns bad on a building project or suppliers fail to turn up with a delivery

• The drawing up on a diagram is time consuming it may be quicker to get on with the project

• The project may be simple and not require a diagram

• They could be external factors that effect the time it takes to complete some tasks like weather on a building site