Airport Extreme with External Drive - new mac air not finding

[selaing]

I have the older Airport Extreme with a Seagate external drive attached via USB wire.
I have it set up working as time machine backup for my MBP.

I would like to "attach" via wireless my new MBA.

What am I doing incorrect? Both laptops are using the same wireless network.

Am I doing something incorrect with the settings?

Help!!

 

[selaing]

update

I unplugged the external drive, took the MBA near the airport extreme and it found it.
all is well.