A taxable extended TDY assignment is a TDY assignment that continues for so long that, under the IRC the employee is no longer considered temporarily away from home during any period of employment if such period exceeds 1 year. You are no longer temporarily away from home as of the date that you and/or your agency recognize that your assignment will exceed one year. That is, as soon as you recognize that your assignment will exceed one year, you must notify your agency of that fact, and they must change your status immediately. Similarly, as soon as your agency recognizes that your assignment will exceed one year, your agency must notify you of that fact and change your status. The effective date of this status change is the date on which it was recognized that you are no longer temporarily away from home as defined in the IRC.
41 C.F.R. §301-11.601