  As COVID-19 transmissions spread worldwide, governments have announced and
enforced travel restrictions to prevent further infections. Such restrictions
have a direct effect on the volume of international flights among these
countries, resulting in extensive social and economic costs. To better
understand the situation in a quantitative manner, we used the Opensky network
data to clarify flight patterns and flight densities around the world and
observe relationships between flight numbers with new infections, and with the
economy (unemployment rate) in Barcelona. We found that the number of daily
flights gradually decreased and suddenly dropped 64% during the second half of
March in 2020 after the US and Europe enacted travel restrictions. We also
observed a 51% decrease in the global flight network density decreased during
this period. Regarding new COVID-19 cases, the world had an unexpected surge
regardless of travel restrictions. Finally, the layoffs for temporary workers
in the tourism and airplane business increased by 4.3 fold in the weeks
following Spain's decision to close its borders.
