Aircraft : Ford 3AT trimotor
By 1920 service extended from New York through Chicago to San Francisco following U S Air Mail Route Number 1. Passengers were squeezed into the mail compartments of biplanes.
With the Air Commerce Act of 1926, the government had decided to oversee aviation in much the same way it regulated the maritime industry.
In 1929, Boeing and NAT introduced trimotor transports designed specifically to carry 12 to 18 passengers in an enclosed cabin. These faster planes cut the cross-country journey to only 28 hours, and increased capacity allowed the airlines to reduce the fare to $259.50 (about US$2,500 in today's dollars). They followed the same route, but what was once known as U S Mail Route Number 1, which was quickly becoming known across the nation as the Main Line.
Commercial aviation got a late start in the United States. By the time U S airline companies began carrying sacks of mail in 1926, overseas carriers were making regularly scheduled passenger flights in 17 European countries, as well as on the continents of South America, Australia, and Africa.