If you hold a green card and know in advance that you must be outside the United States for more than one year, it’s worth applying to USCIS for a reentry permit. This lets you to stay away for up to two years.
You should send in your application before leaving. Your reentry permit will serve as an entry document when you are ready to return. Reentry permits cannot be renewed and can be applied for only inside the United States. If you want to stay away for more than two years, you must return briefly and apply for another reentry permit.
The Nebraska Service Center (NSC) of the U.S. Citizenship and Immigration Services (USCIS) issued an advisement in June 2009 regarding a change in procedures related to requests for rescheduling biometrics (fingerprinting) appointments for applications for reentry permits. The NSC has advised that all applications for reentry permits will be denied if the fingerprinting is not completed within 120 days of filing. The procedures for requesting expedited fingerprinting have not changed. I assume this is due to fact that many Green Card holders living abroad were trying to apply for the permit from overseas. In order to stp the practice, USCIS is trying to impose the strict biometrics schedule to make sure applicants apply form inside the US.
Applicants either have to appear at their scheduled appointments or request to be rescheduled. This request must occur before the appointment date. A request for rescheduling must be accompanied by a reasonable excuse for the inability to appear for the scheduled appointment. Rescheduled appointments are set within a maximum 30-day timeframe. Applicants should plan their travel accordingly, as the announcement is absolute with respect to the 30-day timeframe.
Here is a good tip to avoid one’s green card being considered automatically abandoned under law, it is important to return within one year, at the latest.