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Aircraft Performance
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Read the following case to answer the following questions.
1. What is the scope of the project? What does it deliver?
2. Describe how the project tasks and work are organized.
3. What are the weak points with using bar charts for planning this project? What could cause this
project to fail?
4. What could cause this project to fail, its risks?
A Bar Chart Case Example: An Aircraft Component Project
L-F (Lock-Flouris) controls Inc. is a company that designs and manufactures small electronic
components, particularly for the aviation, defense, and space industries. It has received an order from
an aircraft manufacturer to design and supply electronic control units that will be mounted in or near
the engine bays of a new range of aircraft to be built in both civil and military versions. This small unit
will contain a small number of electronic components, assembled on a printed circuit board, which in
turn will be supported on an aluminum chassis. This assembly is to be encapsulated in epoxy resin to
protect the components from the harsh environmental conditions of the engine bay. A cable connector
and a pressure switch will also be mounted on the chassis, to protrude outside the encapsulated block.
The small project described here is for the design and environmental testing of a small prototype batch.
Our project ends with the issue of drawings for manufacture.
Figure 7.1 lists the main tasks for this project. The estimated duration, stated in days, has been
entered against each task. in each case this is the best estimate of how long each task will take (the
elapsed time), and it does not indicate the resources or work-hours required. The extreme right-hand
column lists, for each task, the immediately preceding tasks that must be completed before the new
task can start.
Figure 7.2 is the resulting bar chart. The planner has tried to observe the dependencies (logical
constraints) given in the final column of the task list. For example, no environmental testing can take
place before the ten prototype units have been made and functionally tested. However, the usual form
of bar chart, shown here, does not allow these logical constraints or links to be shown. These can be
dealt with mentally on this simple project, presenting no problem to a competent planning engineer.
But, with any project of greater size there would be a considerable risk of producing a bar chart
containing some logical impossibility. Also, there is a risk of introducing logical planning errors whenever
the chart has to be rescheduled.
Vertical link lines can be added to bar charts to indicate dependencies (logical constraints)
between two or more jobs. Figure 7.3 is a linked version of the bar chart of figure 7.2. This shows clearly,
for example, that the determination of environmental parameters and main design cannot start before
the customer has specified the project requirements. But some links, even for this tiny project, cannot
clearly be shown on this kind of chart. This applies, for example, to tasks which are dependent on
determining the environmental parameters. Most project management computer programs are capable
of plotting linked bar charts, but the results are usually cluttered and difficult to interpret except for very
tiny projects.
This project will be revisited later in this chapter to see how much more effective it would be for
the L-F controls company to plan its work with critical path networks.
Bar Charts As Progress Monitoring Aids
Because bar charts are drawn to scale, they can be used to indicate progress. For this purpose a date
cursor must be added, which is a vertical line placed on the chart at the review date (which is sometimes
called ‘time-now’). If the chart is drawn or printed on paper, the date cursor can be formed by placing a
straight edge or ruler vertically on the chart at the time-now date. Adjustable charts set up as wall charts
often use a scarlet elastic cord or ribbon for the cursor line. Progress assessment is simply a matter of
checking that all tasks (or portions of tasks) lying to the left of the date cursor have been completed.
Late jobs are highlighted clearly by this method.
Bar Chart Limitations
The inability of bar charts to depict clearly the dependencies between different tasks has been
demonstrated but bar charts have other limitations. Although it is possible to schedule more than 100
jobs using a proprietary adjustable wall chart, rescheduling is a different story. Setting up a complex plan
in the first place might take a few working days but adjusting it subsequently to keep in step with
changes might prove impossible. However, a project management computer system will solve this
inflexibility problem.
For those who prefer to see their project plans always presented as bar charts, all competent project
management software can convert plans using critical path networks into their equivalent bar charts,
either with or without the links shown.
The visual effectiveness of a chart is lost when too many color codes are introduced, or when
there are so many tasks shown in one view that it is difficult to trace their positions along the rows and
columns.
Critical Path Networks
The idea for critical path networks germinated in several places before the Second World War,
but it was in the US during the 1950s that they were fully exploited. They became more popular in the
1960s when suitable computer systems became available with which to remove the drudgery of
scheduling and (particularly) rescheduling.
Network diagrams show all the logical interdependencies between different jobs. The planner
can ensure, for example, that a set of tires is not scheduled for fitting before the wheels manufacture
has been completed and the tires have been purchased. Such logical inconsistencies are easily possible
with complex bar charts, where it is impossible to depict or see every logical constraint.
Another great strength of networks is that they allow priorities to be quantified, based on an
analysis of all the task duration estimates. Those tasks that cannot be delayed without endangering
project completion on time are identified as critical tasks, and all other tasks can be ranked according to
their degree of criticality.
Networks cannot be used by themselves for resource scheduling. in this respect bar charts are
superior and easier to understand, provided that the number of activities is very small. However, one
important value of networks is that they assign time-based priorities to tasks and highlight critical jobs.
That is a vital contribution to the resource scheduling process, and critical path network analysis is an
essential precursor to resource scheduling. Resource scheduling is described in Chapter 8. Most project
management software can schedule resources.
Even if no duration estimates are made and there is no time analysis, the benefits derived from
drawing a network can be worthwhile. Networking encourages logical thinking. A planning meeting can
be regarded as a productive form of brainstorming. it greatly helps to develop the project process. Not
only does the network notation allow expression of all inter-activity dependencies and relationships, but
there is also the important possibility that activities may be brought to light which might otherwise have
been forgotten, and thus excluded from schedules, estimates, cost budgets, and pricing.
Reference
Flouris, Triant; Lock, Dennis. Aviation Project Management.
Abingdon, Oxon, GBR: Ashgate Publishing Ltd, 2008.
ebrary collections. 18 Jun. 2014

Copyright © 2008. Ashgate Publishing Ltd. All rights reserved.
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