Approving the TNA does not approve the course, it only approves the TNA and prevents any further editing. Any data the TNA shares with the TMD will no longer be updated when the data in the TMD changes.
When you save the change in Status of the TNA to Approved, the required Business Rules will run to check whether any fields are missing information. Any identified issues are listed on the Business Rules Results screen. In order to save the change in status, the following TMD fields require some data to be entered:
•Foreword
•Purpose of Initiative
Note: You cannot unapprove a TNA, so only set the Status to Approved if required. Once you have approved the TNA, you can create a Modification TNA, which will create a new TNA with the current data of the TMD for you to modify.
Lock - the Alternative to Approving the TNA
If you want to prevent changes to the TNA, but still want the ability to update the TNA later, you can Lock 
the TNA. The Locked Status means that the TNA is complete and has been reviewed. No one can edit the TNA and any related content without having the Unlock privilege to allow them to unlock the TNA.
Note: Locking the TNA will split it off from the TMD, so any changes made in the TMD will NOT be reflected in the TNA. If you want to resync the TNA data with the TMD data at any point, Lock both of them separately, then Unlock 
the TNA. That will ask you whether you want to delete the TNA data and resync with the TMD data. Click OK and the TNA data will resync with the TMD data, while keeping any TNA specific data intact.