As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE REPLACING FLEXIBLE DUCT AT COMPRESSOR OUTLET STACK ON NR 1 PACK HEAT EXCHANGER, NOTED CRACK ON OUTLET STACK 12 O'CLOCK POSITION STARTING APPROX 2 INCHES INSIDE OF STACK HEADING DIRECTLY INBD FOR APPROX 1.5 INCHES. *S/D* REPLACED HEAT EXCHANGER.