Jordan Porter, 38, faces forgery, identity-theft and other counts and has raised national-security concerns among investigators, CNN reported Sunday.
"We don't really know who he is," a prosecutor said at Saturday's bail hearing in Miami. "When you are refusing to identify yourself to the FBI and you're working in an airline, that's a concern."
WFOR-TV, Miami, said Porter refused to reveal his true name to the FBI and was called a flight risk by prosecutors.
Porter is employed by American Eagle Airlines and was allegedly carrying a falsified passport and driver's license when he was questioned by the FBI. He was identified only as a native of Guyana, CNN said.
Details as to why Porter came under FBI scrutiny were not immediately released.