Just spoke with a SWA representative. The PTC stands for "Passenger Type Code". She instructed me to use the code ADT for Adult. Even though we have minors age 13-17 travelling with adults, she instructed me to use ADT for everyone since that code represents that everyone in our group is paying a standard fare. She also indicated that I should NOT fill out the Title column, and that I should use all capital letters (as the example shows) when typing in names.
