The Citation X has a Mmo = 0.92. The required pad for FAA requirements is 0.07. We had to fly to Md = 0.99 during envelope expansion and flutter testing. We used a T-38 as a chase plane (the one that was in the Pepsi commercials, N38CT owned by Chuck Thornton).
During the dive testing, we did exceed Mach 1.0, but were not required to by FAA regulation. As a result, we renamed a conference/meeting room at Cessna the "Mach 1". In it we have pictures of military/commercial supersonic aircraft. The Citation X is also pictured there.
Boeing Flown: 701,702,703;717;720;721,722;731,732,733,734,735,737,738,739;741,742,743,744,747SP;752,753;762,763;772,773.