What was found
AT CRUISE ALTITUDE JUST PRIOR TO TOD HYD 3 LO PRESS CAUTION MSG DISPLAYED. ASSOCIATED INBD GND SPLRS MSG DISPLAYED. RAN POM PROCEDURE, UNABLE TO ESTABLISH SYS 3 PRESS. PERFORMED ALTERNATE LG EXTENSION. REF PILOT WRITE UP AML PG 3197921-1 3A CB POPPED IN FLIGHT. R & R 3B HYD PUMP PRESS SWITCH IAW AMM 29-34-01, PN OFF & ON 967008-1, SN OFF 5004, SN ON HYD 9724. OPERATIONS CHECKED GOOD. R & R 3A HYD PUMP IAW AMM 29-12-03, PN OFF & ON 66195-01, SN OFF K1925, SN ON K2959. OPERATIONS CHECKED FAILED. REF AML PG 3197923-1 FOR EL OF 3A HYD PUMP. IN FLIGHT 3A HYD PUMP CB POPPED IN AVIONICS BAY. RESET ALT EXTENSION HANDLE IAW 05-51-31. DEFER 3A HYD PUMP IAW MEL 29-12-1, PLACARD INSTALLED & MM02 UPDATED. REF DISC NR 2 FOR CAT II DEFERRAL. EMER WAS DECLARED.