MacBook Air unable to write to external Harddisk
MacOS does not natively write to NTFS. Although it has write drivers installed, which can be activated via the command line following this set of instructions, this is complicated. Most users install a third-party driver such as OSX Fuse or Tuxera to write to NTFS. The only file systems that natively support read and write on MacOS, Windows, and Linux are ExFAT and FAT32.