Airlines of Pan American Since 1927 by Gene Banning (2001)

 

A more comprehensive history of Pan American World Airways will likely never be written. The author was a Pan Am captain and historian, in whose name (along with Dave Abrams) an annual research grant was awarded by the Pan Am Historical Foundation. An absolutely invaluable reference, and fun reading to boot.

https://www.amazon.com/Airlines-Pan-American-since-1927/dp/1888962178