This activity is used to define interchangeability codes which are used when defining position alternates and template alternates against the template structures. For each interchangeability code, a rule must be selected in order to define what is to be performed. Interchangeability rules are used when a part or a serial is installed in a serial structure.There are five predefined interchangeability rules.
| Interchangeability Rule | Description |
| One Way Interchangeable | The old part number may be used as the replacement, but only where the old part number was installed. A new part number is an acceptable replacement for either an old or new part number. Example: Part number A is the prime installed part of a certain position in the structure, and part B is a valid alternative. With this rule you can replace part A with part A, and you can replace part A with part B, but you cannot change back to part A from part B. |
| Two Way Interchangeable | An old or new part number may replace either an old or new part number when one of the
parts is removed. Example: Part number A is the prime installed part of a certain position in the structure, and part B is a valid alternative. With this rule you can replace part A with part A, you can replace part A with part B, and you can change back to part A from part B. You can also replace part B with part B. |
| Not Interchangeable | When a part number is removed, it cannot be replaced with the part number defined as
not interchangeable. Example: Part number A is the prime installed part of a certain position in the structure and part B is defined as not interchangeable. With this rule you cannot replace part A with part B. |
| Interchangeable as a Set | This rule is identical to the One Way Interchangeable rule but applies only to
structure positions with a quantity greater than one. It defines interchangeability for the entire quantity
as a group. Under this rule, the old part number may only be used to replace a position where it was
originally installed. The new part number is fully interchangeable and can replace either the old or new part
number, regardless of what was previously installed. However, once a position has been updated with the new
part number, it cannot be changed back to the old part number. Example: Part number A is the originally installed (prime) part in a structure, and part number B is a valid alternate. With this rule, you can replace A with A. You can replace A with B but you cannot replace B with A once B is installed. |
| Qualified Interchangeable | To be used when the other four rules do not apply. This rule will be handled in the same way as the interchangeability rule Two Way Interchangeability, but each replacement will require an approval before the installed alternate is considered usable. |
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