IIRC, Aperture used to do this -- simultaneously save tethered images to the camera card -- but it was a few versions back. At some point Aperture stopped doing it. Unfortunate IMO since it provided a built-in backup of the tethered images.
If anyone has found a way to restore this functionality, I'd like to hear about it.
If you are concerned about backing up the images on your Macbook Air out in the field, you could do an automator folder action that would copy the images from your import folder to an external hard disk or USB stick as they are imported.
Of course you can import the images from your Air to your Pro when you are done, but it's obviously not as easy as inserting a card.