Why would seamen be exempt and airmen be taxed?
Crew Members of Foreign Vessels Compensation for personal services paid to nonresident alien individuals who are temporarily present in the United States as regular crew members of a foreign vessel engaged in transportation between the United States and a foreign country, or a possession of the United States, shall not be subject to U.S. taxation.
https://www.irs.gov/individuals/inte...ns-from-income