Hi @qzliu 

Modifications are used in MRO and Fleet operations module and for example, modifications in aviation refer to the changes, alterations, or upgrades made to an aircraft's structure, systems, components, or interior. Here you can maintain the updates on serial structures or documents as well (e.g., user manuals for serial parts). For modifications with the Documentation assignment type, only the Definition and Structure Impacts tabs will be applicable.

Modification requirement can be based on a service bulletin, airworthiness directive etc.

For more details, please refer the help documentation which might help you.

http://clouddocs/ifsdoc/Greenhouse/Documentation/en//default.htm?searchpage=page/DefineModification/Form

Best Regards,

Thilini