(U.S. Air Force photo by Tech. Sgt. Heather Redman)

Members of the Tucson Police Department and the Davis-Monthan AFB Honor Guard came together to post the colors during the 9/11 Tower Challenge at the University of Arizona Football Stadium in Tucson, Ariz., Sept. 9, 2016. The 9/11 Tower Challenge is held every year in honor of all those who lost their lives on 9/11 and the first responders and military members who continue to serve today.

(U.S. Air Force Photo by Tech. Sgt. Heather R. Redman/Released)

Military members and spouses of 12th Air Force (Air Forces Southern) joined the Tucson community during the 9/11 Tower Challenge at the University of Arizona football stadium in Tucson, Ariz., Sept. 11, 2015. The 9/11 Tower Challenge was held to honor those who lost their lives during the Sept. 11, 2001, attacks and to show their support first responders and military members who continue to protect the U.S. from foreign and domestic threats. During the 9/11 Tower Challenge, participants climbed 2,071 steps representing the number of steps that were in the Twin Towers.

(U.S. Air Force Photo by Tech. Sgt. Heather R. Redman/Released)

Capt. Brandon Liabenow, 12th Air Force (Air Forces Southern) executive officer, carries the U.S. flag across the University of Arizona football field during the 9/11 Tower Challenge in Tucson, Ariz., Sept. 11, 2015. The 9/11 Tower Challenge was held to honor those who lost their lives during the Sept. 11, 2001, attacks and to show their support first responders and military members who continue to protect the U.S. from foreign and domestic threats. During the 9/11 Tower Challenge, participants climbed 2,071 steps representing the number of steps that were in the Twin Towers.

(U.S. Air Force photo by Tech. Sgt. Heather Redman)

Explosive Ordnance Disposal members joined over 1,000 active and retired first responders, military members, and their family members for the 9/11 Tower Challenge at the University of Arizona Football Stadium in Tucson, Ariz., Sept. 9, 2016. The 9/11 Tower Challenge is held every year in honor of all those who lost their lives on 9/11 and the first responders and military members who continue to serve today.

(U.S. Air Force photo by Tech. Sgt. Heather Redman)

Reserve Officer Training Corps members from the University of Arizona joined over 1,000 active and retired first responders, military members, and their family members for the 9/11 Tower Challenge at the University of Arizona Football Stadium in Tucson, Ariz., Sept. 9, 2016. The 9/11 Tower Challenge is held every year in honor of all those who lost their lives on 9/11 and the first responders and military members who continue to serve today.

(U.S. Air Force photo by Tech. Sgt. Heather Redman)

Over 1,000 active and retired first responders, military members, and their family members participated in the 9/11 Tower Challenge at the University of Arizona Football Stadium in Tucson, Ariz., Sept. 9, 2016. The 9/11 Tower Challenge is held every year in honor of all those who lost their lives on 9/11 and the first responders and military members who continue to serve today.

(U.S. Air Force photo by Tech. Sgt. Heather Redman)

Over 1,000 active and retired first responders, military members, and their family members participated in the 9/11 Tower Challenge at the University of Arizona Football Stadium in Tucson, Ariz., Sept. 9, 2016. The 9/11 Tower Challenge is held every year in honor of all those who lost their lives on 9/11 and the first responders and military members who continue to serve today.

(U.S. Air Force photo by Tech. Sgt.

Lt. Gen. Chris Nowland, 12th Air Force (Air Forces Southern) commander, gives opening remarks before the 9/11 Tower Challenge at the University of Arizona Football Stadium in Tucson, Ariz., Sept. 9, 2016. The 9/11 Tower Challenge is held every year in honor of all those who lost their lives on 9/11 and the first responders and military members who continue to serve today.