Is it possible to jailbreak the 64 bit iPad Air 2 with 8.1.3?
Not currently. You can read about how 8.1.3 has patched the loopholes required to jailbreak 8.1.2 and 8.1.1 on jailbreak nation's web site:
- Version 8.1.3 patches the exploits used in TaiG and PP Ghost causing a permanent loss in jailbreaking until another exploit is found (which can easily take months).
I'm sure someone will update things if another exploit is possible, but unless you can revert to 8.1.2 you might be out of luck indefinitely.