The lexicon of the top500 ( The Encyclopedia for Classification Codes ) explains the codes and definitions in the world of economical classifications.
CPC Code 66 Air transport services
The CPC Code 66 is described as
Air transport services
It belongs to the code group
CPC Code 6 Distributive trade services; lodging; food and beverage serving services; transport services; and utilities distribution services
To this Code "66" belongs the sub codes
CPC Code 661: Air transport services of passengers