What was found
THE AIRCRAFT BEGAN ITS TAKEOFF ROLL, AT TAKEOFF POWER THE WHEELS BROKE GROUND AND THE PRESSURIZATION BEGAN TO DRIVE THE CABIN TO SEA LEVEL. THE CABIN BEGAN TO PRESSURIZE AT A RAPID RATE WITH BLEED AIR FORM THE ENGINES ON POWER UP. NO POSITIVE REASON WAS IDENTIFIED. THE AIRCRAFT RETURNED TO THE DEPARURE RAMP AND THE MX DEPARTMENT PERFORMED A CABIN PRESSURIZATION OPERATIONAL CHECK IAW THE LEAR 60 MX MANUAL, 21-30-00, PAGE 215. NO DEFECTS WERE NOTED, AND THE DISCREPANCY COULD NOT BE DUPLICATED. THE AIRCRAFT WAS RELEASED AND RETURNED TO SERVICE. (M)