Are all plans executed exactly as is?
Probably only very few plans are. In most cases the
actual execution is quite removed from the original
The most obvious cause for being unable to follow a plan/schedule is
Murphy. In other words, we have a lot
of uncertainty in our environment. Too many unexpected
events occur and disrupt the ability to execute
the planning as is. Those
disrupting events are not fully "unexpected." They usually do not
surprise us; it is just
that we could not know a priori, at the planning stage,
what would happen and
Are we troubled by our inability to follow the plan as
is? We certainly should be, because it creates a lot of
fires and eventually we don't perform as well as we might.
Moreover, the need to change the planning poses a problematic
Let's consider the following example.
Suppose you are the foreman responsible for a certain
stage in the production. A detailed finite capacity
schedule is generated every week, taking into account
the standing firm orders, the forecast, and the resource's
utilization. According to the schedule, you should now work on
Product A. However, you have just been notified
that a certain material is missing. How come? That's
a question that should be asked later. Right now, expediting
efforts are taken to bring in the missing materials
as soon as possible, with a good chance of it being
all ready tomorrow morning.
What do you do? There are several options:
• Wait until the materials arrive tomorrow.
Start to process the next instruction on the sched
ule, which would be Product B. However, the processing of that batch
is particularly long—a whole
Start processing Product B, but when the materials for
Product A arrive, change over to Product A, and when
you finish, set up the machine again for Product B.
Start processing the third instruction that still ap
pears on your list. This is Product C, which suppos
edly needs to be processed only sometime next week.
However, all the materials are available and process
ing Product C takes only two days.
Of course, setup considerations might have a significant
impact on the decision. But there is one more question
of method. Should we look for a decision that will
least affect the planning, or should we look for the overall