Narrative:

With reported high temperatures and a full passenger load planned, I was checking my gross weights manual for maximum allowable takeoff weight (maximum ATOG). Given the conditions, 100 degree F and 30.08 altimeter, my book showed a maximum ATOG of 118,300 pounds. Our computer-generated weight manifest showed 120,400 for the same conditions. I called our dispatch (sector 36) to resolve the conflict and was told that, yes the computer showed 120.4. I rechecked my book several times, and each time came up with 118.3 or 118.4. The captain and I discussed this discrepancy with the dispatcher, and were told that the computer was more accurate since it's updated more often. So we planned to use the figures given to us, through dispatch, from the computer. As it turned out, the final load, to include children (half-weights), put our actual tog at 117,500 pounds. Halfway through the flight we were selcaled by dispatch. We were informed that the book was apparently accurate and that the computer figures were wrong. The dispatcher made the comment that 'san francisco' (our engineering department who loads the data for the computer) 'has done this to us before'. We have filed an internal, company report to preclude this happening one more time. Lessons learned: 1) what a computer tells me (or tells someone else who passes it along to me) is not necessarily accurate and should always be confirmed. 2) in the event where the computer tells me one thing and my publications tell me another, and I'm sure my book is up to date, I will believe what the book tells me unless given compelling reasons to do otherwise. 3) computes make humans lazy, or at least complacent. 4) I salute the dispatcher for calling us back with feedback that he had been snookered also.

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Original NASA ASRS Text

Title: COMPUTER GENERATED ALLOWABLE GROSS TKOF WEIGHT FOR MLG AT DEN LESS ACCURATE THAN BOOK FIGURES.

Narrative: WITH REPORTED HIGH TEMPS AND A FULL PAX LOAD PLANNED, I WAS CHECKING MY GROSS WEIGHTS MANUAL FOR MAX ALLOWABLE TKOF WEIGHT (MAX ATOG). GIVEN THE CONDITIONS, 100 DEG F AND 30.08 ALTIMETER, MY BOOK SHOWED A MAX ATOG OF 118,300 LBS. OUR COMPUTER-GENERATED WEIGHT MANIFEST SHOWED 120,400 FOR THE SAME CONDITIONS. I CALLED OUR DISPATCH (SECTOR 36) TO RESOLVE THE CONFLICT AND WAS TOLD THAT, YES THE COMPUTER SHOWED 120.4. I RECHECKED MY BOOK SEVERAL TIMES, AND EACH TIME CAME UP WITH 118.3 OR 118.4. THE CAPT AND I DISCUSSED THIS DISCREPANCY WITH THE DISPATCHER, AND WERE TOLD THAT THE COMPUTER WAS MORE ACCURATE SINCE IT'S UPDATED MORE OFTEN. SO WE PLANNED TO USE THE FIGURES GIVEN TO US, THROUGH DISPATCH, FROM THE COMPUTER. AS IT TURNED OUT, THE FINAL LOAD, TO INCLUDE CHILDREN (HALF-WEIGHTS), PUT OUR ACTUAL TOG AT 117,500 LBS. HALFWAY THROUGH THE FLT WE WERE SELCALED BY DISPATCH. WE WERE INFORMED THAT THE BOOK WAS APPARENTLY ACCURATE AND THAT THE COMPUTER FIGURES WERE WRONG. THE DISPATCHER MADE THE COMMENT THAT 'SAN FRANCISCO' (OUR ENGINEERING DEPT WHO LOADS THE DATA FOR THE COMPUTER) 'HAS DONE THIS TO US BEFORE'. WE HAVE FILED AN INTERNAL, COMPANY REPORT TO PRECLUDE THIS HAPPENING ONE MORE TIME. LESSONS LEARNED: 1) WHAT A COMPUTER TELLS ME (OR TELLS SOMEONE ELSE WHO PASSES IT ALONG TO ME) IS NOT NECESSARILY ACCURATE AND SHOULD ALWAYS BE CONFIRMED. 2) IN THE EVENT WHERE THE COMPUTER TELLS ME ONE THING AND MY PUBLICATIONS TELL ME ANOTHER, AND I'M SURE MY BOOK IS UP TO DATE, I WILL BELIEVE WHAT THE BOOK TELLS ME UNLESS GIVEN COMPELLING REASONS TO DO OTHERWISE. 3) COMPUTES MAKE HUMANS LAZY, OR AT LEAST COMPLACENT. 4) I SALUTE THE DISPATCHER FOR CALLING US BACK WITH FEEDBACK THAT HE HAD BEEN SNOOKERED ALSO.

Data retrieved from NASA's ASRS site as of August 2007 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.