The US Federal Aviation Administration (FAA) will investigate the cause of the cockpit windshield of a Delta plane to shatter mid-air during a flight on Thursday to Washington, D.C., from Salt Lake City, Utah. The 757 made a safe emergency landing in Denver at around 11:35 a.m. on Thursday “after the crew declared an emergency due to a cracked windshield,” the Federal Aviation Administration spokesperson said in a statement. A Delta spokesperson said in a statement that there had been a “maintenance issue mid-flight” but did not elaborate.