This one has bitten me every time I have installed either Ubuntu or Lubuntu on a Mac. This post is now the one I refer to each time should I forget the three steps it takes to resolve this problem. Depending on your situation, you may only need two terminal commands and a reboot.
So its for a very specific Macbook air? My 2015 Macbook Pro let me use wifi as soon as it was installed, Ubuntu and Linux Mint were the ones i tried
Mine is a Macbook Pro 2013 with a Broadcom wireless device.