I'm going from memory here... Aux1 is Flap. So talking about Aux1 is also referring to Flap. They can't be separated. If you have set your wing to dual servo, then the Aux1/Flap channel is reserved for the second aileron servo. Check the wing config is set for single servo, that will make the Flap/Aux1 channel available. Also, you can't choose a switch for Flap/Aux1 if that switch is set for one of the other channels (Aux2, 3, or 4). You can safely "INH" them (inhibit) for Aux2, 3, and 4. This should give you access to choose any available switch you want under the Flap channel. I love JR radio's but their menus drove me nuts, so I migrated to Spektrum. Their newer stuff is much better though.
Since the 9503 is only a DSM2 radio, you must use a receiver that can do DSM2. I'm pretty sure most Spektrum DSMX receivers are backward compatible. If it will bind, then you're good to go.
Good luck!
Last edited by BluMiniMe; 01-26-2019 at 08:42 AM.