A2 Operations Management

Critical Path Analysis

How long will it take?

Walls have decided to launch a new Magnum ice cream. Machine delivery will take 9 weeks, installation takes 5 weeks, staff recruitment 4 weeks and training a further week. Suppliers need 2 weeks lead time and the trial production run will take 2 weeks.

How long until the new magnums will be in the retailers fridges?

Answers? 22 weeks? Longer? Shorter?

Prepare a grid.

Activity Preceded by Duration

A Delivery - 9

B Installation A 5

C Recruit - 4

D Train C 1

E Supply - 2

F Trial B,D,E 2

Answer

Critical Path Analysis

The process of planning the sequence of activities in a project in order to discover the most efficient and quickest way of completing it.

Widely used in industries such as construction where it is possible to operate a range of activities in parallel

By mapping out the network of different activities firms can see which activities can be run at the same time

It also allows firms to see which activities can not be delayed without holding up the overall project

Critical Path Analysis involves constructing a network diagram.

A node denotes the start and finish of an activity. It is split into 3 sections

An arrow represents an activity which is labelled and put above the arrow. Each activity has a duration which is put underneath the arrow.

Number of the node. Provides a unique identity 1

Earliest start time (EST) that an activity can commence and depends on the completion of the previous activity

A

5 days

Latest finishing time (LFT) of the previous activity without delaying the next activity

This diagram represents a project with four activities - A,B,C and D. D can not start until C has been completed.

A

B

C D1 2 3 4

Student activity

Draw a network using the following information: A,B and C begin together. D follows A, E follows B, F follows C and E.

Answer

A

B

C

D

E F

Constructing a critical path network

Prerequisite - the activity that must be completed before our selected activity can occur. E.g. digging foundations for a house before building the walls

Constructing a critical path network

Step 1: Draw a node to represent the start of the network. All networks

must start and end with a node. Do not draw a node at the end of an

activity line immediately, ensure it is right first. A node represents the

point at which a new activity can begin.

Step 2: Identify activities with no prerequisites. Draw lines from left to

right from node 1.

Step 3: Label activity lines with description and duration

Step 4: Move onto the first activity with a prerequisite. Place a node at

the end of the line and draw the next activity which is reliant on the

previous activity being completed.

Step 5: Repeat steps 3 and 4 until complete. Then calculate the ESTs

and LFTs. Then the critical path can be established.

Constructing the Critical Path Analysis

Earliest starting time (EST) - Move forward through the nodes

and always pick the largest of the options. Work right choosing

the highest option for each node.

Latest finishing time (LFT) - move back from the final node

and always pick the smallest of the options. Work left choosing

the lowest option for each node.

The Critical Path

The sequence of activities that cannot be delayed without delaying the overall completion of the project.

It is represented by activities that have identical LFTs and ESTs and it is the longest path between nodes.

Student activity - Complete the critical path analysis for the following project. Identify the critical path.

Activity Duration (days) Prerequisite(s)A 5 -B 3 -C 4 BD 2 C

Answer

The critical path is B, C, D

A

5

B

3

C

4

D

22 3 41

00 3

3 77 9

9C

4

B

3

D

2

Tips

Always ask your self the question: What activity can I do next?

A node is like a full stop. It must go at the end of an activity, it does not represent an activity

Critical path analysis - Lesson 2 - Recap

Critical path analysis is a way of showing how a lengthy and complex project (e.g. a building project, marketing campaign) can be completed in the shortest possible time.

It shows which of the activities are ‘critical’ - this means that if these activities are delayed, then the project will not be able to be completed on time.

Student Activity - Produce a critical path for the following project. Identify the critical path.

Activity Duration (days) Prerequisite(s)A 6 -B 7 AC 5 AD 3 CE 8 CF 4 B,DG 2 E,F

Answer Step 1 - Draw the activities and nodes in the correct order Step 2 calculate the ESTs and LFTs EST - Earliest the next activity can begin LFT - latest finishing time that the previous activity can finish without

delaying the next activity

BA

C D

E

F G1 2

3

4 5 6

LFT

EST

0

Node 1 always start with an EST of zero and should have an LFT of zero

0 6

6

EST = Previous EST plus activity length (between node 1 and 2: 0 + 6 = 6)

If you have a choice between two different EST values as at node 4 choose the biggest

11

11

19

19

21

21614

15

LFT = work backwards subtracting the activity from the previous LFT if there is an option choose the smallest value

24

3

8

5

7

Step 3 - Label the Critical Path

The critical path is the sequence of activities that cannot be delayed without delaying the overall project completion.

It is represented by the activities with identical ESTs and LFTs and the longest path between the nodes

The critical path for the previous example would be: Critical path A,C,E,G

On the diagram the critical path activities will be symbolised with two lines through the activity line

Float Times Float time - the amount of time that non-critical activities within

a project can be delayed without affecting the deadline for

completion of the whole project.

Total float for an activity- the amount of time an activity can be

delayed without delaying the whole project

Total Float for an activity= LFT -EST - duration of the

activity

E.g. Activity D = 15 - 11 - 3 = 1 day

Therefore the activity may be delayed by 1 day without affecting

the whole project

Critical Path Analysis

Produce a critical path network for the following Marketing campaign. Calculate the EST, LFT, critical path and total float for each activity

Activity Description of activity Duration PrerequisiteA Plan the advertising

campaign4 -

B Make a TV advert 6 AC Make a poster 7 AD Test market the TV video 8 BE Test suitability of the poster 10 CF Present the campaign to the

board9 D, E

G Communicate campaign towhole company

5 F

A

Calculating float timesB

321

00 3

3

Float for the activity = LFT – EST - Duration

Float for this activity = 3 – 3 - 0 = 0

D

853

1013 21

21

Float for this activity = 21 – 10 - 8 = 3

Float times for Marketing strategy activity

A = 4 - 0 - 4 = 0

B = 13 – 4 – 6 = 3

C = 11 – 7 – 4 = 0

D = 21 – 13 – 8 = 0

E = 21 – 11 – 10 = 0

F = 30 – 21 – 9 = 0

G = 35 – 30 – 5 = 0

Student Activity

Complete the exam question 2 a) for January 2005 Unit 4 exam paper

Answer January 2005 Question 2a)

Problems of using CPA

Can encourage rigidity

If every activity is strictly time-tabled a delay in a critical activity

may result in a greater overall delay

CPA focuses on speed of completion rather than quality

CPA relies on estimated completion times

Complex projects may be difficult to produce

Sub-contractors are outside of the firms control and may not

stick to deadlines

Supplies may be delayed

Business Implications of Critical Path Analysis

1. Read and highlight the information on the business implications of using CPA

2. Complete questions 1 and 2 on the information sheet

For both critical path questions calculate all ESTs, LFTs, the critical path and the float time of each activity