Conclusion

There is no doubt that travels by air is affected by COVID-19.

5.1 People’s moods are affected by COVID-19

People are more positive in terms of travel by air at the beginning of this pandemic.
People become more negative as time went by.

Through sentiment analysis we know that sentiment of people are unstable. They tends to be more positive at first. They might be confident and thought COVID would all ends really soon. And then they become more negative cause it didn't end at all.

5.2 Only a part of travelers are finally stopped by COVID-19

Travelers are stopped most at the beginning of this pandemic.
Travelers made up their minds as time went by.

By combining flights dataset with CDC dataset we know that COVID-19 did stopped people traveling, but not significantly. They are mostly stopped at the beginning of this pandemic, and as time went by, people who decided to travel by air still travel.