This specific version (5.1.5621) is tailored for a precise set of hardware. If you have a newer model, you likely need version or the modern Boot Camp 6.x series. Supported Models: MacBook Air: 11-inch and 13-inch (Mid 2011 to Mid 2012).
If you are encountering missing drivers or hardware issues after installing Windows, this driver package is likely the solution. boot camp support software 515621
For most users, it is best to let the on your Mac automatically download the correct software. Only manually download 5.1.5621 if you are performing a manual installation on a machine specifically from 2010–2012. This specific version (5