By David Shepardson WASHINGTON (Reuters) -Boeing Chief Executive Dave Calhoun said Thursday there is still a chance U.S. regulators could approve the 737 MAX 10 before the end of the year and he thinks the company will win approval for the smaller 737 MAX 7 in the coming months. Boeing faces a late December deadline set by Congress to win certification of the two variants of the MAX before a new safety standard on cockpit alerts takes effect. “We are working to finish. There’s a chance but there’s also a chance it doesn’t,” Calhoun told reporters on the sidelines of an aviation event. Calhoun …