FLC OF A B727 OPERATED THE ACFT WHEN IT DID NOT MEET AIRWORTHINESS STANDARDS DUE TO 2 OF THE 3 TURBINE ENG THRUST REVERSERS WERE PLACARDED OTS. HOWEVER; THE ACFT FLT LOG DID NOT INDICATE THE ACFT WAS OTS; BUT ONLY THAT IT WAS LIMITED TO UNCONTAMINATED RWYS. MAINT PERSONNEL ADVISED THE FLC AFTER FLT.

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THIS RPT IS IN REGARDS TO FLT XX (DEN TO TUS) AND FLT YY (TUS-DEN). FLOWN ON MAR/XA/98. THE ENTIRE CREW SAW THAT 2 OUT OF 3 ENG'S THRUST REVERSERS HAD BEEN DEFERRED AND PLACARDED. THEREFORE; WE DILIGENTLY READ THE MEL PLACARD INFO PROVIDED TO US BY OUR MAINT DEP BEFORE PROCEEDING ON THE FLT. FOR EACH THRUST REVERSER WE READ THAT THE ONLY LIMITATION WAS TO NOT GO TO ANY CONTAMINATED RWY (IE; WATER; SNOW; SLUSH) WITH REVERSERS SAFETY WIRED IN A FORWARD THRUST POS. WITH THE INFO PROVIDED TO US WE BELIEVED THAT WE WERE IN COMPLIANCE WITH ALL MEL PLACARD INFO AND THAT WE WERE OK TO PROCEED ON THE AFOREMENTIONED FLT SINCE ALL RWYS WERE CLR AND DRY. UNFORTUNATELY; OUR MAINT DEPT SUBSEQUENTLY DISCOVERED THAT IT IS NOT PERMISSIBLE TO HAVE 2 THRUST REVERSERS DEFERRED AT THE SAME TIME. ONCE AGAIN; BASED ON INFO PROVIDED TO THE PLTS WE THOUGHT WE MADE THE RIGHT DECISION. IN THE FUTURE; OUR MAINT DEPT NEEDS TO BE MORE VIGILANT ABOUT MEL AND ASSOCIATED PLACARD INFO SINCE; AT OUR AIRLINE; WE DO NOT CARRY A COPY OF THE MEL ON BOARD.