"Airline service between Iran and the United States last operated in 1979, when the U.S. government imposed an embargo on flights following the Iran hostage crisis. Since then, travel and air cargo shipments between the two countries have been routed through third countries, and their extent has been limited by U.S. sanctions. The July 2015 agreement in which Iran accepted strict limits on its nuclear program in exchange for a broad lifting of U.S., European Union, and United Nations sanctions has raised the prospect that bilateral air service could resume. However, air travelers should not expect to catch direct flights between the United States and Iran any time soon. Generally speaking, airlines provide international services on the basis of bilateral or multilateral agreements among governments. The U.S. Department of Transportation (DOT) Office of the Assistant Secretary for Aviation and International Affairs, with assistance from the U.S. State Department, is responsible for negotiating air service agreements and awarding U.S. airlines the right to offer services provided for in those agreements."
CRS Insight, IN10399
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html