Our Macbook Air is running Mavericks. Disk Utility does not see the drive either.
Have tried installing Installer 1.3.6 but this doesn’t see the drive either. 
The drive works fine on my old Mac running OS 10.6.8
If your disk drive is not password-protected, then it is possible the Apple MacBook Air is not providing enough power to feed your WD Passport. I would recommend using a USB Power Booster Cable, which can be identified as USB cable shaped as the letter “Y”.
We’re using the cable which came supplied with the drive. I’ve just found the cost of the cable is way too expensive so I’ll have to send the drive back for a refund.
