ACR MDT LANDED WITH THE #1 HYD SYS OUT OF FLUID. WHEN PARKED; WAS CHKING THE OPS MANUAL TO DETERMINE IF THE CVR AND FDR SHOULD BE CANCELED. ACFT ENDED UP WITH ONLY 1 HYD SYS PWRING THE RUDDER AND SHOULD HAVE SAVED THE RECORDERS.

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AFTER LNDG DUE TO A #1 HYD SYS TOTAL FLUID LOSS; WE (FO AND MYSELF) SEARCHED THE OPS MANUAL TRYING TO DETERMINE IF THERE WAS A REQUIREMENT TO PRESERVE THE CVR AND FDR. WE DETERMINED THAT THAT WAS NOT NEEDED. WE THEN PROCEEDED TO SPEAK WITH THE DISPATCHER WHO SEEMED TO THINK THAT IT WAS AN NTSB RPTABLE INCIDENT WHICH WOULD REQUIRE US TO PRESERVE THE CVR AND FDR; THEN THE ODM MADE THE DETERMINATION THAT IT DID NOT QUALIFY AS A RPTABLE INCIDENT. I AM NOT SURE MYSELF IF IT DID NEED TO BE RPTED BECAUSE AFTER READING THE MANUAL AGAIN; IT SAYS 'INFLT FAILURE OF HYD SYS THAT RESULTS IN SUSTAINED RELIANCE ON THE SOLE REMAINING HYD OR MECHANICAL SYS FOR MOVEMENT OF FLT CTL SURFACES.' THIS ACFT IS A DHC8 WITH MECHANICAL AILERONS AND HYD ROLL SPOILERS. THE #1 SYS ONLY TOOK OUT THE INBOARD ROLL SPOILERS AND ONE OF THE RUDDER ACTUATORS. AFTER LOOKING AT THE WORDING I REALIZED THAT THE RUDDER ON THE DHC8 IS ALL HYD AND THEREFORE WAS DOWN TO ONLY 1 ACTUATOR AT THE TIME THE #1 SYS FAILED. I FEEL THAT IN THE FUTURE; IF AN OCCURRENCE CANNOT BE DETERMINED EASILY TO BE RPTABLE OR NOT; I WILL PULL THE FDR AND CVR BREAKERS RIGHT AWAY WHILE THE DECISION IS MADE ONE WAY OR THE OTHER.