SAN FRANCISCO - A federal district court did not abuse its discretion when it declined to estop United Airlines and Continental Airlines from opposing airline ticket purchasers' national market definition, the Ninth Circuit U.S. Court of Appeals ruled Jan. 16 in an unpublished opinion affirming the dismissal of the purchasers' complaint challenging the airlines' merger under Section 7 of the Clayton Act (Michael Malaney, et al. v. UAL Corporation, et al., No. 12-15182, 9th Cir.; 2014 U.S. App. 880).