Temporary duty assignment

A temporary duty assignment (TDA), also known as "temporary duty travel" (TDT), "temporary additional duty" (TAD) in the Navy and Marine Corps (or TDI for "temporary duty under instruction," referring to training assignments), or "temporary duty" (TDY) in the Army and Air Force, refers to a United States Government employee travel assignment at a location other than the employee's permanent duty station. This type of secondment is usually of relatively short duration, typically from two days to 179 days in length. Not all agencies use this designation. Some government agencies including the Defense Department mandate they be less than six months in duration. Those agencies that do not mandate a six-month limit consider longer durations to be a Permanent Change of Station (PCS).