 Complete the following phrase:  The SR-71 was the worlds fastest and highest-flying air-breathing operational manned aircraft throughout its career. On 28 July 1976, SR-71 serial number 61-7962, piloted by then Captain Robert Helt, broke the world record: an absolute altitude record of . Several aircraft have exceeded this altitude in zoom climbs, but not in sustained flight. That same day SR-71 serial number 61-7958 set an absolute speed record of , approximately Mach 3.3. SR-71 pilot Brian Shul states in his book The Untouchables that he flew in excess of Mach 3.5 on 