CPM-200: Principles of Schedule
Management
Lesson B : Critical Path Scheduling Techniques
Instructor
L. Sue Cooper
562-797-4655
Leila.r.cooper@boeing.com
15th Annual International Integrated Program Management Conference
November 16-19, Tyson’s Corner Virginia
Professional Education Program (Training Track) presented by
PMI-College of Performance Management faculty
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Schedules Foundation of EVMS
SCOPE
( Technical )
SCHEDULE
( Time )
BUDGET / COST
( Resources )
$
$
$
$
$
$
$
The products/services the
contractor has agreed to
provide
Period of
Performance
$
The planned/actual
expenditure of
resources
Schedules must be interrelated with scope and cost. All three pieces must be accurate
to maintain an integrated baseline for successfully completing a given job.
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Objectives
 The objectives of this presentation are to discuss the
– Scheduling Process
• Understanding of the schedule development process and the
importance of a valid schedule
– Developing a Schedule Network
• How to construct a Precedence Diagramming Method (PDM) logic
network
• The different types of relationships between activities
– Network Calculations
•
•
•
•
Define the meaning of critical path
Identification of the schedule critical path
How to calculate total float and free float
The difference between total and free float
– Schedule Baseline
• Understand why a baseline is necessary
• Baseline change approvals
– Status Updates
• Accomplishment versus forecast
– Schedule Traceability
• Definitions
• Importance
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Schedule Topics
 Scheduling Process
 Developing a Schedule Network
 Network Calculations
– Critical Path
– Total Float
– Free Float
 Schedule Baseline
 Status Updates
 Schedule Traceability
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Planning/Scheduling
Planning (Think)
– Defines the activities involved in the
project, their logical sequence, and their
interrelationships
Scheduling (Do it)
– Places the project and each of its activities
in a workable timetable
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The Scheduling Process
 Define the objective – think
 Establish the organizational structure – think
 Establish the key milestones required to satisfy the
objective – think
 Put key milestones in order of occurrence – schedule
 Define the activities required to accomplish the work – think
 Establish the logical relationships of the activities
–
Calculate/analyze – schedule
 Estimate the duration of each activity – think
 Validate technical content, identify risks
– Make adjustments, as appropriate - think/schedule
 Commitment and approval
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Importance to Program Management
 Common tool for project communication
 Schedule baseline development
 Critical path identification/analysis
 A “snapshot” of program accomplishment to
date
 A look ahead at the forecast of completion
 Basis for EAC development
 Schedule risk analysis
 “What if” analysis tool
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Precedence Diagramming Method (PDM)
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Developing a Schedule Network
 A graphical representation of a project showing
interrelationships of activities
 When time estimates and computations are added
– become the project schedule
B
C
D
E
A
J
F
G
H
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Developing a Schedule Network
Engineering
WBS No. First Engineering task in the
schedule for WBS 1011 = 01
E 1011 01
5
Design Drawings
Logical link to
other tasks
P 1011 01
10
Planning
 Activities must be coded so they can be easily
identified and found in the schedule database
 Every activity must have
– Brief description
– Duration
– Relationship to other activities in the schedule
 Smart Codes add capability
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Developing a Schedule Network
IMP Event
Accomplishment
Criteria
Task Number
A 01
a
10
A01a 20
5
Complete Staffing
Logical link to
other tasks
10
Identify SPO Team
 IMP example
– Event A, Post Award Conference
– Accomplishment 01, IPTs staffed and chartered
– Criteria a, IPT Contractor/Govt Team Members
Identified
– Task No., Supporting Tasks
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Developing a Schedule Network
All tasks must have the Predecessor/Successors identified
Engineering Drawing
Release Complete
Design Drawings
Predecessor
ER
Planning
Tooling
Activity
Successor
– Predecessor Activity Code
– Successor Activity Code
– Relationship
Start-to-Start (SS)
Finish-to-Start (FS)
Finish-to-Finish (FF)
– Lag
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Developing a Schedule Network
Relationship types
Finish-to-Finish
* Finish-to-Start
A
B
A
B cannot start until A finishes
B
* Most commonly used.
80-85% of the relationships in
a network are FS
B cannot finish until A finishes
A
Start-to-Start
B
B cannot start until A starts
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Let’s Create a Network
Task A initiates the project
Task A precedes tasks B, C and D
 Tasks B and C precedes E
 Tasks C and D precede task F
 Tasks E and F precede task G
 Task G completes the project
Task A
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Let’s Build a Network
B
E
A
C
G
F
D
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Determine Durations
B
5
E
ATP
A
3
C
Contract
Complete
3
G
F
D
4
1
2
4
How long will each activity take to complete?
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Critical Path Method
Contract
Complete
ATP
Project
Duration
Early Dates
Late Dates
Total Float
Free Float
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Critical Path Method
 Critical Path Method (CPM)
– A scheduling technique that defines all project
activities and their interrelationships
 Critical Path (calculated)
– Longest path of logically related activities through
the network which has the “least” Total Float
– Defines project duration
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Calculating the Critical Path
6
5
B
4
E
C
ATP
Contract
Complete
4
3
D
A
H
6
6
F
7
G
Critical Path Duration = 25 Time Units
Path A-B-D-H
=
19 Time Units
Path A-F-G-H
=
22 Time Units
Critical Path
(25 Time Units)
Add up the durations along each path to Contract Complete
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Network Calculations
 Forward Pass
– Calculates the earliest an activity can be done based on the
logical relationships and durations
– Identifies the longest path through the network which is the
‘critical path’
– Every activity will have an Early Start (ES) and an Early Finish
(EF) when the forward pass is complete
 Backward Pass
– Calculates the latest a task can be done based on the logical
relationships and durations before affecting the end date
– Every activity will have a Late Start (LS) and a Late Finish (LF)
when the backward pass is complete
 To calculate the Total Float the Forward and Backward
pass must be complete
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Network Calculations–Forward Pass
Adding activity
duration to Early Start
gives Early Finish
ES + Duration -1 = EF
ES
EF
1
3
3
4
6
3
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Produces
• Early Start
• Early Finish
for each activity
21
Forward Pass
Start with day 1
1
5
6
A
9
F
C
0
Start
2
H
1
3
B
7
4
D
G
5
E
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Forward Pass
Day 1 plus 6, -1 = 6
ES
1
EF
6
6
Next activity starts on the next day
7
A
11
5
12
20
9
F
C
21
22
0
Start
2
3
1
4
10
3
B
11
14
7
H
4
D
G
4
8
5
E
Every activity has an Early Start and an Early Finish
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Network Calculations–Backward Pass
LS = LF - Duration + 1
15
2
4
Subtracting activity
duration to Late Finish
gives Late Start
Produces
10
13
14
15
LS
LF
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• Late Start
• Late Finish
for each activity
24
Network Calculations–Backward Pass
6
5
A
9
F
C
22
0
2
Start
H
3
B
7
4
G
D
22
Start with the latest
Early Finish (EF)
5
E
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Network Calculations–Total Float
7
6
1
11
6
20
9
5
A
1
12
F
C
6
7
11
12
20
21
22
The LF of the preceding activity is one day earlier
0
2
Start
1
3
3
4
11
9
10
16
4
17
H
14
4
G
D
B
7
10
7
21
22
Late Finish – duration + 1
20
8
5
E
12
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Network Calculations–Total Float
The amount of time an activity can be delayed or expanded before
it impacts the project end date.
Difference between Early Finish and Late Finish calculates Float.
EF
45
ES
15
30
15
15
30
60
LS
LF
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Network Calculations–Free Float
The amount of time an activity can be delayed or expanded before it
impacts the next activity.
Difference between the early start of the next activity minus the early
finish of the preceding activity (minus 1) defines free float.
4
10
7
D
FF = 0
4
EF = 8
5
E
FF = 2
ES = 11
EF = 14
4
F
FF = 0
15
25
10
G
Will occur only when multiple
activities constrain a single activity.
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Network Calculations –Total Float
7
6
1
11
5
6
A
12
F
C
1
6
7
20
9
11
12
20
21
22
0
2
Start
1
3
4
10
B
4
D
9
10
21
G
16
4
H
14
7
3
7
11
17
22
20
8
5
E
12
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Network Calculations - Total Float
TF = 0
1
TF = 0
TF = 0
6
11
6
5
A
12
20
9
F
C
TF = 0
1
6
7
11
12
20
21
22
0
Start
2
TF = 6
1
4
10
3
7
11
4
D
9
14
7
B
10
21
G
16
4
H
TF = 6
TF = 6
3
TF = 8
17
22
20
8
5
E
12
16
Is there any ‘Free Float’ in this network?
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Network Calculations – Free Float
TF = 0
TF = 0
1
11
6
5
A
1
TF = 0
6
12
9
F
C
6
7
20
TF = 0
11
12
20
21
22
0
Start
2
3
3
4
10
7
B
7
FF = 6
11 TF = 6 14
TF = 6
TF = 6
1
4
G
D
9
10
17
16
FF = 2
4 TF = 8
H
21
22
20
8
5
E
12
16
Is there any ‘Free Float’ in this network?
Look at E & G
Look
At G & H
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Network Calculations -Total Float
TF = 0
TF = 0
1
11
6
5
A
1
TF = 0
6
12
9
F
C
6
7
20
TF = 0
11
12
20
21
22
0
Start
2
1
3
3
4
10
11
4
G
D
9
10
17
16
4
TF = 8
H
14
7
B
7
TF = 6
TF = 6
TF = 6
21
22
20
8
5
E
12
16
Notice – The Critical Path is also the
path with the least amount of float
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Network Calculations – Calendar
Activity
Preceding
Activity
A
B
C
D
E
F
G
H
A
B
B
C
A
F
D, E, G
Succeeding
Activity
Activity
Duration
Start
Complete
B, F
3
Apr 1
Apr 5
C, D
E
H
H
G
H
5
6
4
4
6
6
7
Apr
Apr
Apr
Apr
Apr
Apr
Apr
Apr
Apr
Apr
Apr
Apr
Apr
Apr
6
11
11
17
6
12
21
10
16
14
20
11
17
27
Look at activity A – Duration of 3 with a
start of Apr 1 & complete Apr 5????
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Network Calculations–Calendar
1
1
Thu
Activity starts on
the first instant
of Day 1
Activity A
2
2
Fri
3
Sat
4
Sun
3
5
Mon
Non work
days
Duration
3
Start
Apr 1
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Tue
Next activity starts
on the first instant of
next day
Complete
Apr 5
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Time Phased Bar Chart
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Critical Path Definitions
 Critical Path is the longest path
 The path that defines minimum project time
– The path with the least amount of float
– The path on which any activity expansion/delay
lengthens the duration of the project
 Total Float
– The amount of time an activity can move with
out impacting the end date
 Free Float
– The amount of time an activity can move with
out impacting another activity
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Schedule Baseline
 A coordinated and approved schedule/plan.
 Used to measure status against.
 When integrated with cost the result is the
Performance Measurement Baseline (PMB)
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Schedule Baseline
 Schedule Baseline can change as a result of:
–
–
–
–
Contract Change Orders
Customer Redirection
Internal Replanning
Formal Reprogramming
 Baseline changes require formal authorization
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Status Updates
 Identify completed tasks
 Identify and status activities in process
(remaining duration)
 Identify estimated start dates for tasks which
were scheduled to have started prior to report
date but have not
 Check for activities worked out of sequence
Status updates do not require formal approval
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Status Updates
STEP 1. HOW MUCH WORK WAS ACCOMPLISHED?
Time Now
(Accomplishment)
STEP 2. WHEN WILL THE WORK COMPLETE?
Time Now
(Forecast Completion Date)
Measured against the approved baseline schedule
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Status Updates
What do I need to know to ‘status’ the schedule?
 Time now
 Actual dates:
– Start date
– Finish date
 Accomplishment
 Remaining duration
(how long it will take to finish)
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Status Updates
 Determine a “forecast” start or finish
– For activities started but not finished:
• Remaining duration, how much longer will it take to
complete the work
– For activities scheduled to finish but are behind
schedule:
• Remaining duration
• Assess the impact to succeeding activities in the network
– For activities not started:
• Impact of preceding activities
• Assess the impact to succeeding activities in the network
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Recovery Plan
A recovery plan does not replace the baseline schedule.
Tasks may be re-sequenced, resources realigned, or effort redirected to reduce
the current behind schedule conditions to the maximum extent possible.
 Requires program coordination between IPTs and Scheduler
 Forecast dates on the schedule must be consistent with time
phased “Estimate To Complete” (ETC)
 Status continues against the baseline schedule
Time Now
Currently behind schedule but the baseline
completion date will be met.
Baseline completion date will not be met.
The ETC phasing should be consistent with
the schedule forecast dates
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Status Updates
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Schedule Traceability
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Schedule Traceability
 The ability to readily track schedule dates,
durations, status and revisions at all levels of
schedule detail and between schedules at the
same level of detail
– Horizontal Traceability
– Vertical Traceability
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Schedule Traceability
 Horizontal Traceability
– A schedule dependency between performing
organization
– Hand-offs between organizations, teammates,
subcontractors
– Activities are dependent upon a preceding
activity
• Predecessors have been identified
• Successors have been identified
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Horizontal Traceability
Tooling
What does it look like?
Planning
Fab
Assembly
Procurement
Delivery
Section
Release
ATP
Eng
Release
Manufacturing
Design
Start
Engineering
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Vertical Traceability
 A relationship between different levels of
schedule detail
– All milestones that appear on a higher level schedule
must be supported by the lower level schedules
– Higher level schedules typically constrain lower level
schedules
– Different levels schedules must be linked by reference
– All levels of schedules must be integrated
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Vertical Traceability
What does it look like?
2.1
WBS
Level 2
2.1.3
Ctr Bod y
Str
2.1.5
Engine
System
2.1.6
Avionics
System
2.1.2
Tank Assy
WBS
Level 3
Common Booster Core
2.1.4
Thrust
Structure
2.1.7
Propulsion
System
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2.1.8
Thermal
System
2.1.9
Mech
System
Intermediate
Schedule
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Schedule Traceability
 Hand offs between organizations not properly
coordinated or formalized (horizontal)
 Level of detail schedules are not consistent
 No top down schedule direction
 No formalized process for linkage or roll-up
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Schedule Traceability
 To achieve schedule traceability a formalized scheduling
process must be in place for all ‘players’
– Common use of data fields by all participants
– Utilization of same processing cycle
– Disciplined status collection
– Disciplined Baseline change control
 Strong interdivisional/functional coordination
 Strong management support
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