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2. Bureau of Transportation Statistics. U.S. Airlines Show First Profit Since COVID-19 in 2nd Quarter 2021 (2021). https://www.bts.gov/newsroom/us-airlines-show-first-profit-COVID-19-2nd-quarter-2021
3. Bureau of Transportation Statistics. Passengers: All Airlines - All Airports (2021). https://www.transtats.bts.gov/Data_Elements.aspx?Qn6n=G
4. International Air Transportation Association. What Types of Cargo are Transported by Air? (2021). https://www.iata.org/en/publications/newsletters/iata-knowledge-hub/what-types-of-cargo-are-transported-by-air/#:~:text=Where%20to%20find%20more%20information,jobs%20are%20always%20in%20demand
5. International Air Transportation Association [IATA]. Air passenger market analysis (2019). https://www.iata.org/en/iata-repository/publications/economic-reports/air-passenger-monthly---dec-2019/