What was found
AS A RESULT OF A RECENT PRESSURE VESSEL INSP, FOUND THE SAFETY VALVE, PN 130406-1, SN 121-2018, DATED 12-22-81 BY LEAR, WAS FOUND TO HAVE A CRACKED NR 1 BOSS. BY DATE AND S/N, THIS VALVE IS NOT AFFECTED BY AD 95-20-03 (LEARJET SB 35-21-19). TO LOCATE CRACK, 'AN' FITTING WAS REMOVED. PRESSURIZATION SYS WAS WORKING NORMALLY, WITH NO INDICATION OF A CRACK. LEARJET CONFIRMED CRACKS NOT ACCEPTABLE AND VALVE REPLACED. SINCE BOTH OUTFLOW VALVE AND SAFETY VALVE HAVE SAME P/N, BOTH VALVES WERE CHECKED. NO CRACKS FOUND IN THE OUTFLOW VALVE. CRACK WAS APPARENTLY CAUSED BY OVERTORQUE SITUATION, OR, OVER A PERIOD OF TIME, CAUSED BY EXTREME TEMP CHANGES. SUBMITTER SUSPECTED OVERTQORQUE POSSIBILITY FIRST.