| Airline | Specify airline to request availability for.Identifies a company by name. |
 BookingClassPref | Specifies specific booking classes to include and/or exclude in the response. |
| FlightNumber | Specific flight number to request availability for. Requires that Airline is also supplied.Identifies a flight number (1 to 4 numbers followed by optional uppercase A - Z, which specifies an operational suffix) or OPEN or ARNK. |
| TPA_Extensions | A placeholder in the schema to allow for additional elements and attributes to be included per Trading Partner Agreement (TPA).Allows extensions to be added to the OpenTravel specification per trading partner agreement. |