Earlier this year a new airline standard was rolled out no longer requiring passengers to declare a gender to fly. Several states provide an ‘X’ option on their IDs for gender.
United Airlines was first to offer both U(undisclosed) and X(unspecified) as a gender option this spring. Since on or about December 10th American Airlines has adopted this standard.
American tells reservations agents, “AACoRN will display a blank space for some AAdvantage customers that don’t have a gender code registered in [CRM system] Ventana. When AACoRN displays a blank space ensure you change the gender code to M, F, U or X as applicable”