United Airlines and Air China will connect more flights, make transfers through gateway airports more seamless, increase joint marketing and expand benefits for top-level frequent-flyers across the two airlines. According to United, senior executives will develop the partnership through regular meetings. United, which flies nonstop from San Francisco to three mainland China airports, will add service to Xi'an on May 8 and, pending government approval, Hangzhou on July 13. This summer, Air China will add a nonstop flight between San Jose, Calif., and Shanghai and add capacity to its Beijing-San Francisco service. Both carriers are Star Alliance members.