At 1722 mountain time, a Cessna 172P and a PA-31T collided in midair over Denver. The pilot and two passengers aboard the Cessna and the two pilots aboard the Piper were killed. Six people on the ground suffered minor injuries from falling debris. The Cessna had departed Centennial Airport about 22 minutes earlier, bound for Cheyenne, Wyo. The Piper departed Jeffco Airport about 12 minutes earlier, bound for Centennial. The Piper was flying VFR to the southeast in Class E airspace at 7,800 feet squawking a discrete transponder code and under radar contact, but the airplanes Mode C altitude readout was apparently missing. The Cessna departed VFR northbound and was cleared into Class B airspace to climb to a cruise altitude of 8,500 feet. The controller asked the Piper to verify altitude, and the pilot reported 7,600 feet. The controller gave a traffic advisory that the Cessna was at 12 oclock, one mile and same altitude. The two airplanes collided head-on. One witness reported the Piper made an evasive maneuver at the last second.