TABLE OF CONTENTS Calculating the number of ways maintenance events can occur is called combinatorial analysis. There are two ways of doing this. Combinations involve finding out how many ways an event can occur, ignoring any duplication of events. Permutations are similar, though only the arrangement of events is taken into account.
Examples:
A recent aircraft modification installed internal valving, which now allows a single point refueling system to fill two (2) tanks at a time, reducing the usual fuel servicing time and the impact on logistics resources.
| Sample Data | |
|---|---|
| A = | Right Wing Fuel Tank |
| B = | Left Wing Fuel Tank |
| C = | Fuselage Fuel Tank |
Find all of the combinations of tanks that can be filled two at a time. The number of n different items taken r at a time (ignoring multiple arrangements) is:
Solution:
| Fuel tanks: | AB | AC | BC |
Find all of the ways that fuel can migrate (flow) between two individual tanks during refueling. The number of n different items taken r at a time is:
Solution:
| Fuel tanks: | AB | BA | AC | CA | BC | CB |
The probability of failure or of having to perform maintenance can be determined using samples of data and a few known facts. It is used where large quantities of data do not exist. Like forecasting weather, the probability of occurrence can be predicted, but it doesn't necessarily mean that the event will or will not happen...
