In traditional assignment techniques of mechanics to machines, the driving indicator has
been machine coverage (Knapp and Mahajan 1998). For instance, a typical policy is to
determine how many mechanics are required such that machines are either running, or are
down but being serviced – the goal is to eliminate a down machine not being serviced by a
mechanic. Given the importance of machines running or capable of running to meeting
production quotas, management policies regarding the assignment of maintenance
mechanics to machines are often conservative and risk-averse. As a consequence, there
is usually an excess of maintenance personnel and thus, the utilisation of the mechanics is
low and having idle mechanics is typical (Hartman 1987). Also in traditional maintenance
systems, mechanics are assigned exclusively to a specific number of machines according to
their skill levels and the machines’ maintenance complexity (Dietz 1997). Therefore, a
mechanic is idle when his set of designated machines does not require any service. On the
other hand, if a fellow mechanic requires assistance because more than one of his
designated machines is down, the idle mechanic still may not assist him as those machines
do not belong to his own assigned list or work zone. Under this type of scenario, it is not
rare to find machines waiting to be serviced, while other mechanics are idle, creating a
variety of issues such as unnecessary non-productive time, additional labour costs,
imbalance of workloads, poor morality and motivation, etc. Even though it may seem
that, as long as there are ‘plenty’ of mechanics, the availability of the machines will be
high. This traditional system of corrective maintenance may hinder the mechanics from
servicing machines out of his assignment or work zone and consequently lowers personnel
utilisation and efficiency (Hartman, 1987). The realised availability of machines is actually
lower due to the inefficiency and rigidity of the static assignment policy.