A Frontier Airlines Airbus arrives at a gate on the A concourse of Denver International Airport in this photograph taken on Tuesday, July 11, 2006. Frontier Airlines Holdings Inc. releases first-quarter earnings. (AP Photo/David Zalubowski) ** FILE **
In this photograph taken late Monday, Feb. 8, 2016, a Spirit Airlines craft waits to take off from a runway at Denver International Airport. (AP Photo/David Zalubowski)
This May 14, 2014 image, provided by Denver International Airport, shows newly-erected signs warning travelers about he danger of the MERS virus, at Denver International Airport. MERS, or Middle East Respiratory Syndrome, is a respiratory illness that begins with flu-like fever and cough but can lead to shortness of breath, pneumonia and death. The airport says the signs were posted Wednesday, May 14, 2014 at all of its screening areas at the direction of the Centers for Disease Control. (AP Photo/Denver International Airport)