Safety checks on some Boeing jets hit a snag over paperwork on Sunday, as U.S. authorities searched for a missing panel that blew off a new Boeing 737 MAX 9 jet in midair on Friday. The Federal Aviation Administration on Saturday ordered the temporary grounding of 171 Boeing jets installed with the same panel after the eight-week-old Alaska Airlines jet was forced to make an emergency landing with a gap in the fuselage. But criteria for the checks have yet to be agreed between the FAA and Boeing, meaning airlines have yet to receive detailed instructions, people familiar with the matter said.