A B737-300 DEPARTED WITH AN 19000 LB TKOF WT ERROR.

Narrative

THE OPS AGENT HANDED ME THE LOAD SHEET AND I BEGAN TO MAKE THE APPROPRIATE ENTRIES IN THE FMC AND OPC. THE CTR COLUMN OF NUMBERS ADDED UP AND LOOKED CORRECT. WE NOTICED AND COMMENTED THAT WE WERE REALLY LIGHT AND WERE GOING TO TAKE OFF LIKE A ROCKET. I GOT THE NUMBERS FROM THE OPC AND HANDED IT TO THE CAPT; WHO THEN CALLED FOR THE BEFORE PUSH CHKLIST. WE RAN IT AND PROCEEDED TO PUSH; START; TAXI AND TAKE OFF UNEVENTFULLY. ONCE IN THE AIR; WE RECEIVED A RADIO CALL FROM OPS TELLING US TO REVISE OUR TKOF WT. PULLED OUT THE LOAD SHEET AND AT THAT TIME NOTICED A LARGE DIFFERENCE IN TKOF WTS. THE CORRECT WT WAS ACTUALLY 19000 LBS HEAVIER. WE THEN REALIZED THE NUMBERS ADDED UP CORRECTLY BUT THE PAX WT WAS EXTREMELY LOW; CAUSING THE LOW TKOF WT. THE OPS AGENT HAD ENTERED 33 PAX INTO THE COMPUTER VERSUS THE 133 PAX THAT WE ACTUALLY HAD. THE ERROR WAS TWOFOLD: 1) GARBAGE IN; GARBAGE OUT FOR THE OPS COMPUTER; THE NUMBERS ADDED UP HAD WE REALLY HAD 33 PAX. 2) WE DID NOT NOTICE THE DISCREPANCY IN PAX LISTED ON THE LOAD SHEET. THE PLANE TOOK OFF FINE; ALTHOUGH THE CAPT SAID IT FELT A LITTLE MUSHY ON LIFTOFF. BUT HAD WE LOST AN ENG ON TKOF AT THAT HVY WT AND AT THAT ALT; WE MAY NOT HAVE BEEN ABLE TO STAY AIRBORNE. WE WERE NOT FEELING RUSHED OR ANY OTHER PRESSURES LIKE THAT. SUPPLEMENTAL INFO FROM ACN 664644: THIS WAS THIS CREW'S 5TH LEG TOGETHER FOR THE DAY. THE FO WAS JUST DOING 1 DAY WITH ME. I WOULD GET A NEW FO AT DEST TO COMPLETE THIS 3-DAY PAIRING. I HAD COMMUTED IN FROM THE CITY THIS MORNING TO FLY THIS 6-LEG DAY. I FELT TIRED AS WE WERE GOING THROUGH OUR PREFLT DUTIES FOR THIS LEG. WE STARTED THE DAY A LITTLE BEHIND SCHEDULE BUT WERE NOW ON TIME. I CAN'T BELIEVE THAT I MISSED THIS LARGE ERROR. I QUICKLY SCANNED THE FORM AND CHKED THAT THE FLT AND TAIL NUMBERS WERE CORRECT AND CALLED FOR THE 'BEFORE PUSH CHKLIST.' I THINK PART OF THE PROB IS THAT WITH THE NEW COMPUTER GENERATED FORM; I HAVE STOPPED LOOKING FOR MATH ERRORS LIKE I DID WITH OLD FORM. THIS CAN CREATE A FALSE SENSE OF SECURITY. YES THE MATH WAS CORRECT -- GARBAGE IN; GARBAGE OUT. I WILL SLOW DOWN A LITTLE IN THE FUTURE AND REALLY LOOK AT THE FORM AND CHK EVERYTHING FOR ACCURACY JUST LIKE WITH THE OLD MANUAL FORM. ON THIS FLT; ALL 3 OF US FAILED TO CATCH A SIMPLE ERROR AND THE CHK AND BAL WE RELY ON BROKE DOWN.