A BE20 CPR PLT FLIES 2 LEGS WITH IMPROPER DOCUMENTATION; FAILING TO ADHERE TO HIS ACFT'S MAX ZERO FUEL WT AND MAX TKOF WT RESTRS FROM OLM; WA.

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ON JAN/FRI/03 AT APPROX XA30 HRS; I DEPARTED THE OLM ARPT WITH 9 PAX AND FULL MAIN FUEL TANKS ENRTE TO BFI. PRIOR TO DEP; I MENTALLY CALCULATED THAT THE AIRPLANE WAS BELOW MAX ZERO FUEL WT AND MAX TKOF WT USING A STANDARD PAX WT OF 175 LBS. DUE TO THE LATE ARR OF SOME PAX; I KEPT CRUISE PWR AT A HIGHER THAN NORMAL FUEL BURN RATE. WE LANDED AT BFI APPROX 30 MINS LATER. WE DEPARTED BFI AT APPROX XD30 ENRTE TO OLM WITH 1 ADDITIONAL PAX; THE SAME DATE. WE LANDED AT OLM APPROX 30 MINS LATER. 1 WK LATER; IT WAS BROUGHT TO MY ATTN BY ANOTHER PLT THAT I MAY HAVE EXCEEDED THE MAX ZERO FUEL WT AND/OR MAX TKOF WT FOR THE AIRPLANE. I PERFORMED THE CALCULATIONS USING AN ELECTRONIC CALCULATOR AND ACTUAL PAX WTS AND DISCOVERED THAT I HAD MADE AN ERROR IN THE ZERO FUEL WT AND TKOF WT FOR BOTH DEPS AND ARRS. THIS ERROR WAS CAUSED BY PERFORMING A MENTAL CALCULATION USING A STANDARD PAX WT OF 175 LBS AS OPPOSED TO USING AN ELECTRONIC CALCULATOR AND ACTUAL PAX WTS. I HAVE SINCE CALCULATED SEVERAL POSSIBLE PAX CONFIGNS (NOT USING STANDARD 175 LB WTS) AND COME UP WITH DIFFERENT ZERO FUEL WT AND TKOF WT FIGURES DEPENDING UPON ACTUAL PAX WTS USED.