Green card holders who spend less than 6 months abroad can usually return to US with no further issues. If you spend more than 6 months but less than 1 year you may be subject to further questioning. if you spend more than 1 year you should have a re-entry permit which allows you to return after spending 1-2 years abroad.
AP is not the correct document for green card holders; it is only for those who are waiting for green cards.
... If you spend more than 6 months but less than 1 year you may be subject to further questioning.
And this questioning can take a long time, so it is normally done in a separate room called secondary inspection.The additional questioning is to establish to the satisfaction of immigration inspector that you have not abandoned US as your place of residence if you stay abroad more than 6 months.