WHEN THE GEAR WAS SELECTED DOWN AT THE OM; THE GEAR ON A BA31 WOULD NOT COMPLETELY EXTEND. THE FLC THEN DISCOVERED THAT THEY HAD LOST ALL HYD PRESSURE AND THEY MISSED THE APCH AND EXTENDED THE GEAR THROUGH THE EMER MANUAL MEANS.

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ON APCH INTO MSP WE LOWERED THE LNDG GEAR FOR THE ILS RWY 11L AT THE OM. THE NOSEWHEEL GEAR CAME DOWN NORMALLY; BUT THEN THE R MAIN TOOK ALMOST 20 SECONDS TO LOCK DOWN IN PLACE AND THE L MAIN WOULD NOT INDICATE DOWN AND LOCKED. BY THIS TIME WE HAD BROKEN OUT OF THE CLOUDS ON THE ILS APCH. WE REQUESTED A FLY-BY OF THE TWR TO SEE IF THE L MAIN GEAR APPEARED TO BE DOWN OR NOT. THE TWR SAID IT APPEARED TO BE DOWN. WE PROCEEDED TO GO MISSED TO WORK OUT THE GEAR PROB. ON CLOSER INSPECTION OF OUR HYD GAUGES; I SAW THAT BOTH PUMP #1 AND PUMP #2 WERE INDICATING 0 PSI PRESSURE. IT WAS AT THIS POINT I REALIZED OUR MAIN HYD LINE HAD PROBABLY BURST (ON POSTFLT THIS WAS CONFIRMED). I FEEL THAT THERE SHOULD BE SOME SORT OF INDICATING LIGHT WHEN HYD PUMP PRESSURE IS LESS THAN THE MINIMUM TO OPERATE THE SYS; BUT THERE IS NO LIGHT. THERE IS A LIGHT FOR OVERPRESSURE ON THE BA3101 HAD SYS. THIS MAKES NO SENSE TO HAVE A WARNING LIGHT FOR OVERPRESSURE; BUT NO WARNING LIGHT FOR UNDER PRESSURE. ALSO; IF SUCH A WARNING LIGHT HAD EXISTED WE WOULD HAVE KNOWN ABOUT THIS PROB BEFORE WE WERE INSIDE THE OM ON THE ILS APCH. WE PROCEEDED TO PUMP THE L MAIN DOWN VIA THE EMER GEAR EXTENSION PROC. WE LANDED WITHOUT INCIDENT ON RWY 11R AND BROUGHT THE AIRPLANE TO A STOP ON THE RWY SINCE WE HAD NO NOSEWHEEL STEERING AND ONLY EMER BRAKING. WE WERE THEN TOWED TO THE GATE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: IF THEY HAD TRIED TO RETRACT THE GEAR DURING THE MISSED APCH; THE WHOLE INCIDENT WOULD HAVE SNOWBALLED. FORTUNATELY; THE FIRST SUSPECT WAS HYDS. IF CREW PROCS HAD NOT BEEN SO GOOD; HOWEVER; A WARNING ANNUNCIATOR WOULD HAVE BEEN THE KEY TO ENSURING THAT THE REMAINING HYD PRESSURE WAS PRESERVED FOR THE ESSENTIALS OF GEAR EXTENSION AND BRAKING. WHAT WAS WRONG WITH THIS AIRPLANE? THE LINE BTWN THE ENG HYD PUMP AND THE ACTUATORS RUPTURED IN THE AREA BTWN THE FUSELAGE AND THE BELLY POD. MECHS BELIEVED THE FAILURE WAS A RESULT OF A SPIKE OF OVERPRESSURE. RPTR ALLUDES THAT WHENEVER A COLD PERIOD ARRIVES THERE ARE USUALLY A FEW ASSOCIATED HYD PROBS.