Is Azan compulsory for offering Sunnah prayers? For Fard prayers it is necessary but can Sunnah prayers be offered before the Azan is called?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions. It is not permissible to perform the Rawatib Sunnah (the Sunnah prayers that have a specific order, number and so on) before the entering of the time of the obligatory prayer by which they are related and are performed before or after those obligatory prayers. Because the Rawatib that are limited to a given time they should be performed only during that time. Therefore, if the Muezzin observes the correct times and does not call unless the actual time of the prayer begins then you are not allowed to perform the Rawatib before Azan. However, if the time has entered and yet the Azan is not called, in this case you may perform the Rawatib Sunan because the criterion is the starting of the specific time not the calling of the Azan itself. However, general voluntary prayers may be performed at any time except the times in which performing prayers is forbidden. For more details in this concern, please read the Fatwa:82719 and 84719. Allah knows best.