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.
You can get the update from the link below or by selecting Software Update from the Apple menu at the top left of your screen.