Excel-Jet officials say it might have been wake turbulence or some kind of freak meteorological event that turned their Sport-Jet prototype on its wing and sent it cartwheeling along the runway at Colorado Springs Airport on June 22. According to a news release from Excel-Jet, witnesses reported the plane rolled 90 degrees about 30 feet above the runway while taking off on its 25th test flight. It struck a wing and cartwheeled onto its tail, causing substantial damage. Both pilots were checked at the hospital and released. The aircraft was nearing the end of its initial round of flight testing and the company had just received word that it had been approved to fly at EAA AirVenture in Oshkosh next month. Excel-Jet CEO Bob Bornhofen said the plane had performed well in previous flights and the company says either wake turbulence or a microburst from unspecified "unusual weather conditions" may have caused the upset. "Sport-Jet has explored the majority of its flight envelope without problems," Bornhofen said. While the program has obviously suffered a major setback, Bornhofen said the silver lining is that the composite cockpit cage proved it protects pilots in a crash. "The carbon roll-cage style designed fuselage of Sport-Jet provided significant protection for its occupants and, according to an insurance expert, was instrumental in minimizing the injuries," the company release said.