One of the most important tables that must be maintained is the principal’s table. All line items on invoices/credit notes and proforma invoices requires you to enter the principal of the service / product.

Quicktrav Invoicing for Windows clearly distinguishes between Air and Land Suppliers

Airline Principals:

Airline suppliers / carriers are created automatically and can import bookings from the reservation system. If the required airline does not yet exist, it must be created manually.

Land Principals :

Accommodation, car hire, cruise, insurance and other suppliers must be created manually and are all created in the same way.