First go on a mission with an anti air wraith on.

Next jump on the wraith were the driver sits then meele the hood until it falls off.

After that meele the drivers head until his helmet falls of (normaly one hit shall do it), then get in a position where it does NOT say "board enemy wraith" (normally crouching down makes it work).

Hold down RB and shoot his head (battle rifles only need one shot to the head infact no other weapon works) then when he dies you will be siting in an anti air wraith.