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 | This rule applies to structure positions where the quantity equals one. With this rule, the old part number may be reused as a replacement, but only in the same 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 reverted to the old part number. For example, part number A is the originally installed component in a specific structure position, and part B is a valid alternate. In this case, you may replace part A with part A, or replace part A with part B. However, once part B has been installed, you cannot change back to part A. |
| 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 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 in the same 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 reverted to the old part number. The behavior differs depending on whether the position is serialized. For serialized positions, the system cannot consistently enforce the interchangeability rule due to the many possible replacement combinations in such positions. A warning is displayed to guide the user that such reversals are not recommended. For non-serialized structure positions, where the entire quantity is replaced as a whole, an error is raised if the rule is not followed. Example: Serialized structure position 101 has quantity of 4, e.g., for fan blades. Part A and part B are set as Interchangeable as a Set.
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| 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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