What was found
AT FL 360 GOT MC LIGHT AND AMBER EICAS ALERT "MAIN CARGO DOOR". DESCENDED TO 10,000' IAW QRH. ALERT EXTINGUISHED AFTER PRESSURE EQUALIZED DURING DESCENT. EMERGENCY DECLARED. RELEASED FOR SERVICE PER MEL : 52-71-01-02 CATEGORY : C EXPIRATION : 01AUG20 "MEL 52-71-01-02: MAIN DECK CARGO DOOR INDICATION SYSTEM - INOP. VERIFY AND RECORD IN AML/EAML THAT MAIN DECK CARGO DOOR IS CLOSED, LATCHED, AND LOCKED BEFORE EACH DEPARTURE." AT BLOCK IN MCD VERIFIED CLOSED, LATCHED AND LOCKED. CYCLED DOOR. NORMAL OPERATION. SEE MTSI 52-70/5444 FOR WORK PERFORMED. REMOVED AND REPLACED PSEU REF AMM 31-70-04-4-99 WITH OPS CKS GOOD.