4. Maintainability Function
M(t)
The maintainability of a unit can be evaluated as follows, using
Eq. (5.71):
and ’ and s_{t '} are given by Eq. (5.88) and (5.91),
respectively.
By means of the transformations
shown in Eqs. (5.90a) and (5.90b), the lognormal distribution of the pdf of
repair times, g(t), is transformed to the standard normal distribution
f(z) which
enables the use of standard normal distribution tables (Table 5.33).
The
maintainability function for the system, M(t), from (5.90)
is:
where:
From the data in Table
5.63 we previously calculated

' =
0.65879
s_{t '}
= 1.11435 

The quantified M(t) is shown
in Figure
5.65. The values were obtained by inserting values for t’ =
ln t into the expression,
solving for z(t’), and reading the value of M(t) directly from
the standard normal tables in Table
5.33.