What was found
AIRCRAFT WAS FLYING UNDER FERRY PERMIT WHEN THE PRESSURIZATION LET GO. DURING CRUISE FLIGHT AT FL410, WE SAW CABIN ALTITUDE RAPIDLY RISING. WE INITIATED A DESCENT & DONNED O2 MASK. A FEW SECONDS LATER, THE CABIN ALTITUDE & MASTER WARNING WENT OFF. INITIATED EMER DESCENT TO 12,000 MSL. PERFORMED ALL GND RUN CHECKS. TROUBLESHOOTING TESTS 1-8, CLEANED BELLY DRAINS, ADJUSTED THE MED SEAL. PASSED CABIN PRESS LEAK RATE AT 75 SECONDS. ALL WORK DONE LAW AMM 21-30-00, 21-10-76, 21-10-35 & 52-11-00. STATIC SYS LEAK CHECKED GOOD LAW AMM CH 34-11-19.