A Chelsea man pleaded guilty Tuesday in federal court in Boston to charges of impersonating a federal air marshal. Abdirahman Y. Hassan, who is in his early 30s, is scheduled to be sentenced in the same court Feb. 11, records show. According to an affidavit filed in the case, Hassan repeatedly told an investigator from his auto insurer in early 2011 that he was a marshal. The investigator was looking into a possible fraudulent claim for vehicle damage Hassan had filed, the affidavit said.Travis Andersen can be reached at email@example.com. Follow him on Twitter @TAGlobe.