One of the few concrete signs of cooperation to emerge from this week's U.S.-China summit could boost Beijing's drive to become a global aircraft maker. President Barack Obama pledged Tuesday to push for closer technical collaboration and eventual U.S. safety approval for China's ARJ21 commuter jet. That amounts to both a symbolic and practical step to counter Beijing's growing frustration with U.S. aviation policy and U.S. restrictions on the purchase of certain technologies. The high-profile U.S. initiative is especially significant because China's own safety regulators are still a year or more away from approving the 70-to-100-passenger aircraft being developed by...