Use this tab to define interchangeability codes. These codes are used when defining position alternates and templates alternates against the serial structure templates. Each interchangeability code requires a rule to describe what it is allowed to do. The following table shows the valid 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 an old part number is removed, it must be replaced with the same part number. When a new part number is removed, it must be replaced with a 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 nothing else. |
| Interchangeable as a Set | Replacing the entire quantity used in one installation. This rule only applies to structure positions where the quantity is higher than 1, and it defines interchangeability for the entire quantity. |
| 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. |