Other than a passport, what types of documents are acceptable for air travel?

Individuals traveling by air within the Western Hemisphere are required to present a passport for admission to the U.S. with limited exceptions. This Final Rule outlines two additional documents that will be acceptable for air travel. The first is the Merchant Mariner Document (MMD) or “z card” issued by the U.S. Coast Guard that will be acceptable for use under WHTI by U.S. citizen merchant mariners traveling on official business. The other document is the NEXUS Air card, for which enrollment is limited to citizens of Canada and the United States, lawful permanent residents of the United States and permanent residents of Canada.