You do the math...
there are approximately 30 cities in the US with a population of 1,000,000 or more. Every minute there is a plane either landing or taking off in each metropolis. Lets say for 16 hours.
16 x 60 = 960 minutes (lets say 1,000 for round numbers)
1,000 x 30 - 30,000 planes taking off and landing in this country.... people are travelling. The market is huge.
I've also seen the stat that at any time there are 5,000 planes in the sky in the US airspace alone. What a market...