A PA42 CHEYENNE III WAS UNABLE TO EXTEND LNDG GEAR WITH NORMAL HYD SYS. GEAR WOULD NOT EXTEND WITH MANUAL SYS; EXTENDED GEAR WITH EMER PNEUMATIC SYS. ON LNDG; R MAIN GEAR COLLAPSED.

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GEAR HANDLE WAS SELECTED DOWN; AND BEFORE LNDG CHKLIST WAS COMPLETED. HOWEVER; THERE WAS NO AURAL OR VISUAL INDICATION OF GEAR OP. ANNUNCIATORS WERE TESTED TO VERIFY ILLUMINATION. I ASKED SIC TO ADVISE TWR OF A POSSIBLE GEAR PROB; AND REQUESTED DELAY VECTORS TO COMPLETE CHKLIST PROCS. I ATTEMPTED TO RECYCLE GEAR. I ASKED THE SIC TO PULL THE CHKLIST FOR MANUAL GEAR EXTENSION. WE COMPLETED THE MANUAL GEAR CHKLIST/PROCS WITH SIC PUMPING. I THEN TRIED TO PUMP. A TOTAL OF +200 PUMPS WERE MADE. GEAR DID NOT RESPOND. I THEN HAD SIC BRIEF PAX; AND I ATTEMPTED TO DO SOME FLT MANEUVERS TO SEE IF GEAR WOULD RESPOND. IT DID NOT. I THEN HAD THE SIC PULL OUT THE EMER PNEUMATIC EXTENSION CHKLIST. WE COMPLETED THE CHKLIST/PROC. GEAR THEN INDICATED L MAIN DOWN AND LOCKED; NOSE DOWN AND LOCKED; NO LIGHT ON R MAIN GEAR. AGAIN; FLT MANEUVERS WERE USED TO TRY AND LOCK THE R MAIN GEAR. I AND THE SIC THEN ADVISED/REQUESTED 'FLY-BYS' FROM THE TWR. AFTER 2 PASSES; TWR ADVISED THAT ALL 3 GEAR APPEARED DOWN. I THEN ADVISED TWR OF OUR LNDG INTENTIONS AND REQUESTED THE EMER EQUIP. I THEN BRIEFED SIC ON LNDG PROCS I WOULD USE; AND WE BRIEFED THE PAX OF EMER AND EVAC PROCS. TWR CLRED US TO LAND WITH THE EQUIP IN PLACE (RWY 36R). WE LANDED AS SOFT AND SLOW AS ALLOWABLE; LOFT MAIN FIRST; FOLLOWED BY NOSE AND R MAIN GEAR. THE ACFT ROLLED OUT BRIEFLY BEFORE THE R GEAR MAIN GEAR COLLAPSED. BOTH ENGS WERE SHUT DOWN PRIOR TO PROP CONTACT ON R SIDE. ACFT THEN PROCEEDED TO SLIP/SKID TO THE R. I USED L BRAKE AND NOSEWHEEL STEERING TO HOLD THE ACFT. THE ACFT SLID OFF THE RWY ONTO THE TXWY; PAST HOLD SHORT LINES.