AN ACR ATR42 CREW FLEW AN ACFT THAT WAS DIFFERENT FROM THE ONE LISTED ON THE DISPATCH RELEASE. ERROR ADMITTED. THE ACR'S OPS SPECS REQUIRE THAT THE RELEASE SHOW THE CORRECT ACFT NUMBER LEADING TO AN FAR VIOLATION IF THE ACFT NUMBER IS WRONG.

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ACFT X WAS FLOWN ON A SCHEDULED PAX FLT FROM STL TO FYV. WE WERE SCHEDULED FOR AN OVERNIGHT. WHEN WE CALLED IN RANGE TO FYV; WE WERE TOLD THAT WE WOULD HAVE TO TAKE OUR FLT BAGS OFF OF THE ACFT BECAUSE IT WAS SCHEDULED FOR A TRAINING FLT THAT NIGHT. WE UNDERSTOOD THIS TO MEAN THAT IF THERE HAD NOT BEEN ANY TRAINING TAKING PLACE; WE WOULD NOT HAVE TO TAKE OUR BAGS OFF OF THE ACFT BECAUSE WE WERE TAKING THE SAME ACFT OUT IN THE MORNING. THE TRAINING CREW MET US AT THE AIRPLANE AND SAID THAT THEY WOULD TRY TO GET THE AIRPLANE BACK WITHOUT BREAKING ANYTHING. THIS ALSO REINFORCED THE THOUGHT THAT WE WERE TAKING THE SAME ACFT OUT IN THE MORNING. WHEN WE ARRIVED AT THE ARPT IN THE MORNING; WE PROCEEDED TO PREPARE FOR OUR FLT TO STL. THE ONLY ACFT ON THE RAMP WAS ACFT X. UPON OUR ARR IN STL; WE WERE TOLD BY THE CREW TAKING OVER THE ACFT THAT WE HAD DEPARTED FYV IN THE WRONG ACFT. A REVIEW OF THE DISPATCH FOR OUR FLT CONFIRMED THAT THIS WAS TRUE. THE ERROR WAS DISCOVERED BY STL RAMP AND OPS; BEFORE WE DEPARTED FYV; WHEN THE ACFT THAT WE WERE SCHEDULED TO FLY ARRIVED IN STL. WHEN THE ERROR WAS DISCOVERED; NO ONE CALLED AND INFORMED FYV OPS. CONTRIBUTING FACTORS: THE CREW TRAINING IN FYV PARKED THE ACFT IN A POS DIFFERENT FROM WHERE WE HAD PARKED IT; AND WHERE IT WAS EXPECTED TO BE PARKED. THIS CONFUSED THE GND CREW IN FYV WHO LOADED THE WRONG ACFT IN THE MORNING. THIS LED THE FIRST CREW INTO THINKING THAT THAT WAS THEIR ACFT. WHEN STL OPS DISCOVERED THE ERROR; THEY FAILED TO PASS ALONG THE INFO. WE ASSUMED THAT THE ACFT ON THE RAMP WAS THE ACFT THAT WE WERE TO FLY SINCE WE HAD FLOWN THE ACFT IN THE PREVIOUS NIGHT. ACFT X WAS ALSO THE ONLY ACFT ON THE RAMP. I FAILED TO XCHK THE ACFT NUMBER AGAINST THE DISPATCH RELEASE. I DID LOOK TO SEE IF AN MEL WAS LISTED AND THERE WAS. WHEN WE BROUGHT ACFT X IN THE PREVIOUS NIGHT; IT ALSO HAD AN MEL. I DID NOT VERIFY THE MEL NUMBER. ALL CONCERNED SHOULD HAVE BEEN ABLE TO CATCH THIS MISTAKE. I WILL DEFINITELY MAKE AN EFFORT TO BE MORE CONSCIOUS AND THOROUGH IN REVIEWING MY DISPATCH AND WILL ALSO NOW REQUIRE THE FO TO REVIEW THE DISPATCH INSTEAD OF JUST ASKING IF THEY WANT TO LOOK IT OVER.