MAA recommends to enable Flashback Database on the primary prior to FailOver:
Enable Flashback Database to reinstate failed production databases after a
failover operation has completed. Flashback Database provides a second
very significant function, enabling fast point in time recovery if needed.
See: MAA_WP_10gR2_SwitchoverFailoverBestPractices.pdf
Enabling Flashback Database involves setting up flash recovery area and setting a flashback retention target which [...]