B727 HAS HYD LOSS INDICATION. COORD WITH MAINT DELAYS THE PROPER COMPLETION OF APPROPRIATE CHKLISTS AND IRREGULAR PROCS.

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DURING CRUISE 'A' HYD SYS QUANTITY WAS NOTED TO BE AT ZERO. THERE WAS NO OTHER ABNORMAL INDICATION. WHEN THE SO BROUGHT IT TO MY ATTN HE MENTIONED THAT HE HAD SEEN IT DECREASE A LITTLE; BUT THOUGHT IT WAS DUE TO COLD SOAKING. HE ALSO MENTIONED THE PUMP LOW PRESSURE LIGHTS WERE NOT ILLUMINATED. WE ACCOMPLISHED ACTION STEPS OF THE HYD LEAK OR LOSS CHKLIST; BUT PRIOR TO PROCEEDING WITH STEPS WHICH WOULD LEAD US TO A SPECIFIC CHKLIST FOR SYS 'A' LOSS I CALLED OUR MAINT COORDINATOR AND DISPATCHER TO DISCUSS THE SIT. AFTER DESCRIBING THE INDICATIONS I ASKED THE MAINT COORDINATOR IF HE THOUGHT WE HAD A HYD FAILURE. HE SAID NO; HE THOUGHT IT WAS AN ERRONEOUS INDICATION AND THE SYS WAS OK. I ASKED HIM A COUPLE OF TIMES IF I UNDERSTOOD HIM CORRECTLY THAT HE THOUGHT THE SYS HAD NOT FAILED. HE REPLIED THAT WAS CORRECT. THE DISPATCHER SAID NOTHING. SOMETHING DID NOT SEEM RIGHT TO ME; BUT I SAID I WOULD CONSIDER THE SYS TO BE OK UNLESS I CALLED THEM OTHERWISE. WE PLACED ALL HYD SWITCHES IN THEIR ORIGINAL POS THUS REPWRING THE 'A' HYD SYS. I ASKED THE SO TO GIVE ME HIS PROC BOOK SAYING THIS DOES NOT SEEM CORRECT. AFTER READING THE PROC A COUPLE OF TIMES ALONG WITH THE FOLLOW-ON CONDITIONAL STATEMENTS; IT BECAME CLR THAT WE HAD NO OPTION; BUT TO CONSIDER THE 'A' HYD SYS TO BE FAILED AND FOLLOW THE 'A' HYD SYS FAILED PROC. WE REACCOMPLISHED THE ORIGINAL PROC AS WELL AS THE 'A' HYD SYS FAILED PROC. I NOTIFIED THE MAINT COORDINATOR AND DISPATCHER OF OUR INTENTIONS ALSO STATING WE WOULD DECLARE AN EMER WITH APCH CTL; STOP ON THE RWY; HAVE MAINT PIN THE GEAR AND TOW US TO THE GATE. AT THIS TIME THE DISPATCHER STATED HE AGREED OUR ONLY OPTION WAS TO CONSIDER THE 'A' HYD SYS TO BE FAILED. (I THOUGHT IT WOULD HAVE BEEN HELPFUL IF HE HAD ENTERED INTO THE DISCUSSION EARLIER INSTEAD OF BEING SILENT). WE DSNDED TO A LOWER ALT AND SLOWED IN ORDER TO ADHERE TO LIMITATIONS FOR 1 YAW DAMPER INOP. FOR THE APCH WE LOWERED THE LNDG GEAR MANUALLY AND USED AN ALTERNATE MEANS OF EXTENDING THE FLAPS AND LEADING EDGE DEVICES. EVERYTHING WENT AS BRIEFED. APCH; LNDG AND TOW IN WERE UNEVENTFUL. WHERE I MADE MY MISTAKE WAS GIVING TOO MUCH IMPORTANCE TO THE HYD LOW PRESSURE LIGHTS AND FLT CTL LOW PRESSURE LIGHTS NOT BEING ILLUMINATED. THAT MAKES NO DIFFERENCE IN THE PROC. WHEN THE QUANTITY DROPS BELOW 2.5 GALLONS YOU MUST ASSUME A HYD SYS HAS FAILED OR HAS A LEAK. THIS WAS NOT MY FIRST HYD SYS FAILURE. IF WE HAD ONLY READ THE ORIGINAL PROC IN ITS ENTIRETY BEFORE CALLING MAINT CTL I WOULD NOT BE WRITING THIS NOW.