Apple today released AirPort Extreme and AirPort Time Capsule Firmware Update 7.7.2 for AirPorts with 802.11ac.
The update includes several different bug fixes, repairing an issue preventing a USB hard drive connected to an AirPort Extreme from appearing as an available disk and fixing an issue that could cause an intermittent loss in WAN connectivity.
Article Link: Apple Releases AirPort Extreme and Time Capsule Firmware Update 7.7.2