What was found
AT BLOCK IN, GOT INTERMITTENT LVL 3 CABIN SMOKE WITH NO ACTUAL OTHER SMOKE INDICATIONS, NOR ANY SMOKE INDICATIONS FROM SENSORS ON AIR SYNOPTIC PAGE. NO FSS ACTIVATION. USED PAN PAN PAN. INDICATIONS WOULD QUICKLY APPEAR, LAST A FEW SECONDS, THEN GO OUT. REPEATED A COUPLE OF TIMES. EMERGENCY DECLARED. REMOVED AND REPLACED #12 SMOKE DETECTOR PER AMM 26-15-01-4, OPS TEST NORM. REMOVED PLACARD.