AN ACR WDB CREW FLEW AN ACFT WITH A MAINT ITEM IMPROPERLY SIGNED OFF BY MAINT.

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DURING PREFLT PREPARATIONS; THE SLAT POS LIGHTS; WHICH INDICATE THE POS OF THE LEADING EDGE SLATS; WOULD NOT TEST USING THE TEST BUTTON ON THE FLAP/SLAT INDICATOR. MAINT PERSONNEL CHANGED INDICATORS; BUT THE LIGHTS STILL WOULD NOT TEST. THE SLATS WERE THEN LOWERED USING THE SLAT FLAP HANDLE; AND PROPER OP OF THE SLAT POS LIGHTS WAS VERIFIED. THE ACFT MEL DID NOT HAVE A LISTING FOR THE TEST FUNCTION OF THE SLAT POS LIGHTS. MAINT CTL AT HEADQUARTERS WAS CONSULTED ON THIS MATTER; AND ISSUED A MAINT CTL DEFERRAL FOR THIS ITEM; WHICH WAS ENTERED INTO THE ACFT LOGBOOK. THE FLT THEN OPERATED WITH THE SLAT POS LIGHTS TEST FUNCTION INOP. I HAVE BEEN UNABLE TO FIND A DEFINITION OF A MAINT CTL DEFERRAL IN THE COMPANY FLT OPS MANUAL; AND HAVE DOUBTS AS TO THE LEGALITY OF DISPATCHING AN ACFT WITH AN INOP FUNCTION WITH NO MEL LISTING TO COVER IT. SUPPLEMENTAL INFO FROM ACN 246456: IT APPEARED TO BE A TESTING PROB ONLY. WE ALSO RECYCLED THE CIRCUIT BREAKERS WITH NO EFFECT. MECHS ALSO CHANGED THE FLAP/SLAT POS INDICATOR WITH THE SAME INCORRECT TESTING PROB.