Part Modeling > Edit Features > Trim > To Trim Using Silhouette Edges
  
To Trim Using Silhouette Edges
1. Select the curved surface to trim.
2. Click Model > Trim. The Trim tab opens.
3. Select any datum plane or planar surface to use as the trimming object.
 
* If you select a solid planar surface as the trimming object, is unavailable. The Silhouette trim method is automatically activated and cannot be deactivated.
4. Click . The silhouette of the curved surface appears.
5. To preview the trim geometry, click .
6. Click .