A key portion of the forecast focuses on projections for the growth in the use of unmanned aircraft, also known as drones. The FAA estimates small, hobbyist UAS purchases may grow from 1.9 million in 2016 to as many as 4.3 million by 2020. Sales of UAS for commercial purposes are expected to grow from 600,000 in 2016 to 2.7 million by 2020. Combined total hobbyist and commercial UAS sales are expected to rise from 2.5 million in 2016 to 7 million in 2020.
Predictions for small UAS used in the commercial fleet are more difficult to develop given the dynamic, quickly-evolving nature of the market. Both sales and fleet size estimates share certain broad assumptions about operating limitations for small UAS during the next five years: daytime operations, within visual line of sight, and a single pilot operating only one small UAS at a time. The main difference in the high and low end of the forecasts is differing views on how those limitations will influence the widespread use of UAS for commercial purposes.
(I only wish they knew how to make a stacked bar graph -- see the abomination at top)