Apple today released EFI Firmware Update 2.7 for the mid–2013 MacBook Air, which comes with several Boot Camp-related bug fixes for the MacBook Airs that were released in June.
MacBook Air EFI Firmware Update 2.7
This update is recommended for MacBook Air (mid 2013) models.
This update addresses an issue which may cause a black screen to appear when installing Windows 7 or Windows 8 using Boot Camp Assistant if both an external optical drive and USB thumb drive are connected to the system. This update also ensures that the system will boot by default into OS X after installation of Windows 8.
The EFI update should be available in the Mac App Store for mid–2013 MacBook Airs and can also be downloaded from the Apple Support site.