https://ppf.ucsf.edu/sites/ppf.ucsf.edu/files/webform/American-Airlines-Customer-Contact-Numbers-Usa-Comprehensive-Official-Guide.pdf https://ppf.ucsf.edu/sites/ppf.ucsf.edu/files/webform/United-Airlines-Customer-Contact-Numbers-Usa-Comprehensive-Official-Guide.pdf https://ppf.ucsf.edu/sites/ppf.ucsf.edu/files/webform/Delta-Airlines-Customer-Contact-Numbers-Usa-Comprehensive-Official-Guide_0.pdf