C-310 EXPERIENCES A PRIMARY ELECTRICAL SUPPLY PROB; IN STAGES.

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DEPARTED SMX APPROX AM00 LCL. MISSION WAS A BUSINESS TRIP SMX DIRECT SQL DIRECT RNO DIRECT SQL DIRECT SMX. ON CLBOUT FROM SMX; NOTED R ALTERNATOR HAD FAILED. L ALTERNATOR WORKING FINE. UPON LNDG AT SQL TO PICK UP MY PAX; INSPECTED R ALTERNATOR AND SATISFIED MYSELF THAT THE PROB WAS NONMECHANICAL AND THE ACFT WAS SAFE TO FLY. ALSO PHONED A&P; DESCRIBED SYMPTOMS; AND MECHANIC CONCURRED. I CONTINUED THE MISSION. NO FURTHER PROBS DURING SQL DIRECT RNO AND RNO DIRECT SQL LEGS. HOWEVER; DURING SQL DIRECT SMX FINAL LEG; ERRATIC LOADMETER INDICATIONS. UPON ARRIVING IN TFC PATTERN AT SMX; LOWERED LNDG GEAR; FLAPS; AND TURNED ON LNDG LIGHTS. LOADMETER INDICATED LESS THAN 50 AMP LOAD ON 100-AMP ALTERNATOR. WHILE TURNING BASE LEG; L ALTERNATOR FAILED. LANDED ON BATTERY PWR ONLY. BOTH ALTERNATORS REQUIRED REPLACEMENT. I SUBSEQUENTLY DISCOVERED THAT 2 ALTERNATORS ARE LISTED IN THE CESSNA T310R 'REQUIRED EQUIP LIST.' CONSEQUENTLY; IT WAS PROBABLY A VIOLATION OF FAR 91.213(D)(II) FOR ME TO HAVE CONTINUED BEYOND SQL WITH 1 ALTERNATOR. IN HINDSIGHT; I SHOULD HAVE RETURNED TO SMX AS SOON AS THE FIRST ALTERNATOR-OUT INDICATION WAS OBSERVED.