Why windshields cracked on at least 14 airplanes at Denver International Airport during a storm last week remains a mystery, prompting the National Transportation Safety Board to call in a glass specialist."We are not discounting anything," Federal Aviation Administration spokesman Allen Kenitzer, whose agency is among those investigating the incident, said Tuesday. "We believe it is very remarkable to have this number of events in the same area at the same time."The National Transportation Safety Board said its glass specialist will examine 22 damaged front and side windshields that were removed from affected airplanes, investigator Jennifer Kaiser said.Wind gusts of up to 50 miles per hour were recorded at the airport and there were rapid temperature changes and some snow Friday afternoon when airlines reported the cracked windshields.Kaiser said the NTSB is also investigating whether an air pressure change may have contributed, she said.DIA spokesman Chuck Cannon said airport operations and maintenance employees could offer no explanation for the windshield problems. "It's baffling," he said.SkyWest Airlines, a regional carrier for United Airlines, reported nine planes suffered windshield cracks, while Frontier Airlines said four of its aircraft suffered similar damage. One plane from Great Lakes Airlines suffered a cracked windshield, Kaiser said.NTSB's Kaiser confirmed that there were no reports of impact from flying debris.