20  Board of Governors of the Federal Reserve System, Indexes of Industrial Production. 21  Of course, the invention and commercial use of the airplane itself was a technological innovation that predated the jet engine. In particular, the introduction of commercial air travel in the late 1920s represented a substantial improvement over existing forms of passenger transportation.
The estimates of Gordon (1992) show that productivity in airline transportation rose about 7 percent per year between 1935 and 1959 as well.