This is a problem. A Lawful Permanent Residency is for someone that intends to permanently reside in the U.S. and is actually doing so. Not for someone that is just coming to the U.S. to visit from time to time.
Anyone that is a Lawful Permanent Resident (LPR) and is outside of the U.S. for 180 days or more within any 12 month period (not necessarily calendar year) creates a rebuttable presumption of abandonment of residency. That presumption can be rebutted by evidence to the contrary such as filing U.S. taxes, maintaining a home in the U.S. and paying that mortgage or rent, maintaining a U.S. drivers license, U.S. bank accounts with significant movement, etc.
Someone that has been outside of the U.S. for more than 1 year without first having an approved re-entry permit has abandoned their residency and only in very few exceptions (such as serious illness) can they get it back.
So if he has made a short trip back to the U.S. every 6 months, he can TRY to renew it, but he has to submit evidence of the things I listed above because to me it looks like he abandoned his Residency status. They call it Residency because he is supposed to be residing in the U.S.
Here is an official link:
The way to renew it would be an I-90, but he should be living in the U.S., not living and working outside of the U.S.
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