1963-77 6c, 8c, 13c, 15c, and 25c

  1963 United Nations Airmail Stamps

These U.N. stamps show the influence of flight.  The 6¢ shows a scene from outer space, the 13¢ is a bird formed from laurel leaves, and the 25¢ cent has an aircraft and an airmail envelope with the U.N. emblem. 

The U.S. Post Office gave up operating its own planes in 1926, after 31 airmail pilots had died in crashes.  They turned to commercial airlines for service.