Data Analysis for Fleet Analysis

Once the accumulated timeline has been generated, it is then converted into grouped data. To accomplish this, a group interval is required. The group interval length should be chosen so that it is representative of the data. (Note: In RGA 6, the interval length is statistically determined using a proprietary algorithm. The analyst should verify that the recommended interval is valid from a practical perspective and alter it if necessary.)

Also note that the intervals do not have to be of equal length. Once the data points have been grouped, the parameters can be obtained using MLE as described in the Grouped Data Analysis subsection of the Duane chapter of this on-line reference. The data in Table 10.2 can be grouped into 5 hr intervals. This interval length is sufficiently large to insure that there are failures within each interval. The grouped data set is given in Table 10.3.

Table 10.3 - Grouped data

The Crow-AMSAA model for Grouped Failure Times is used for the data in Table 10.3 and the parameters of the model are solved by satisfying the following ML equations (Duane chapter).

(22)

(23)

Fielded Systems Example 4

Table 10.4 presents data for a fleet of 27 systems. A cycle is a complete history from overhaul to overhaul. The failure history for the last completed cycle for each system is recorded. This is the random sample of data from the fleet. These systems are in the order they were selected. Suppose the intervals to group the current data are 10000, 20000, 30000, 40000 and the final interval is defined by the termination time. Conduct the fleet analysis.

Table 10.4 - Sample fleet data

Solution to Fielded Systems Example 4

For the system data in Table 10.4, the data can be grouped into 10000, 20000, 30000, 4000 and 52110 time intervals. The grouped data is given in Table 10.5.

Table 10.5 - Grouped data

The ML estimates of and for this data set based on the above time intervals are then given by:

Figure 10.7 shows the System Operation plot.

Figure 10.7: System Operation plot for fleet data

See Also:
Fielded Systems

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