Narrative:

While acting as PIC; my first officer and I inadvertently flew 2 flts with incorrect weight and balance data. The problem arose due to the fact that the official weight and balance data was incorrectly calculated during the aircraft's last weighing and; unbeknownst to us; showed a balance index that was off by about 20 units. During the first flight; we required ballast in order to bring the aircraft into trim range; but this in itself is not uncommon. It was the fact that for the return trip we again required ballast that I contacted the company's maintenance control and was advised that the official weight and balance data in their records matched the data in our aircraft log; and that it was; therefore; correct. At this point; I noticed that the balance index was about 55 instead of the usual low 70's and; therefore; obviously not correct. Having pointed this out; maintenance agreed to contact the weighing facility and ask them to re-check the data. Advised the next flight crew of the situation. As I am unfamiliar with weighing procedures; I cannot comment on how to avoid such mistakes in the future; except that perhaps when new and old weight and balance differ by a certain amount that there automatically needs to be a recalculation and also an explanation of the change.

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Original NASA ASRS Text

Title: A CL600 WAS FLOWN ON TWO FLIGHTS WITH AN INCORRECT WEIGHT AND BALANCE. THE CALCULATIONS WERE OFF BY 20 UNITS BECAUSE OF AN INCORRECT WEIGHING.

Narrative: WHILE ACTING AS PIC; MY FO AND I INADVERTENTLY FLEW 2 FLTS WITH INCORRECT WT AND BAL DATA. THE PROB AROSE DUE TO THE FACT THAT THE OFFICIAL WT AND BAL DATA WAS INCORRECTLY CALCULATED DURING THE ACFT'S LAST WEIGHING AND; UNBEKNOWNST TO US; SHOWED A BALANCE INDEX THAT WAS OFF BY ABOUT 20 UNITS. DURING THE FIRST FLT; WE REQUIRED BALLAST IN ORDER TO BRING THE ACFT INTO TRIM RANGE; BUT THIS IN ITSELF IS NOT UNCOMMON. IT WAS THE FACT THAT FOR THE RETURN TRIP WE AGAIN REQUIRED BALLAST THAT I CONTACTED THE COMPANY'S MAINT CTL AND WAS ADVISED THAT THE OFFICIAL WT AND BAL DATA IN THEIR RECORDS MATCHED THE DATA IN OUR ACFT LOG; AND THAT IT WAS; THEREFORE; CORRECT. AT THIS POINT; I NOTICED THAT THE BALANCE INDEX WAS ABOUT 55 INSTEAD OF THE USUAL LOW 70'S AND; THEREFORE; OBVIOUSLY NOT CORRECT. HAVING POINTED THIS OUT; MAINT AGREED TO CONTACT THE WEIGHING FACILITY AND ASK THEM TO RE-CHK THE DATA. ADVISED THE NEXT FLT CREW OF THE SITUATION. AS I AM UNFAMILIAR WITH WEIGHING PROCS; I CANNOT COMMENT ON HOW TO AVOID SUCH MISTAKES IN THE FUTURE; EXCEPT THAT PERHAPS WHEN NEW AND OLD WT AND BAL DIFFER BY A CERTAIN AMOUNT THAT THERE AUTOMATICALLY NEEDS TO BE A RECALCULATION AND ALSO AN EXPLANATION OF THE CHANGE.

Data retrieved from NASA's ASRS site as of May 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.