Narrative:

We were a delayed departure on a scheduled flight due to the replacement of a worn brake. The determination was made not to replace the worn brake (due to difficulty in mounting the new brake), but instead to deactivate the worn brake and dispatch the flight with a deactivated brake. There are two methods of deactivating the brakes, and both methods incur some performance limitations for takeoff and are addressed in the flight manual. When I checked the performance limitations, I advised the captain that we would be unable to takeoff at the planned gross weight with the brake deactivated at the method planned. The captain left the cockpit and discussed the matter with dispatch and maintenance for 20-30 mins. When he returned, he advised me that dispatch had different performance numbers than the flight manual. We also called up takeoff performance numbers on the cockpit datalink, and they agreed with the dispatch numbers. The captain decided to use the dispatch/computer numbers as the correct ones, and the takeoff and flight were made without incident. After the trip pairing was complete, the captain investigated the matter further with the intent of correcting the flight manual. During the course of his investigation, he learned that the flight manuals were correct, the computer generated numbers and dispatch numbers were wrong. He is proceeding with actions to disclose this discrepancy to both the airline and the FAA, and to correct the dispatch and computer performance numbers. My lesson learned: if there is a discrepancy in operational guidance from different sources, either positively resolve the discrepancy or use the most conservative of the guidance. Supplemental information from acn 339305: unfortunately, it was dispatch data versus flight manual data. Based on the fact that we use so much computer generated data daily (such as weight manifest/takeoff data), the captain elected to accept the dispatch data for takeoff. The result of accepting the dispatch computer generated takeoff weight data was takeoff at approximately 102500 pounds over maximum allowable for that runway.

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Original NASA ASRS Text

Title: AN ACR B747-400 CREW RPTS THAT IT MADE AN ILLEGAL OVERWT TKOF BECAUSE THE PERFORMANCE FIGURES PROVIDED BY DISPATCH AND MAINT WERE FAULTY. ACFT EQUIP PROB MAIN WHEEL BRAKE DISABLED PER MEL.

Narrative: WE WERE A DELAYED DEP ON A SCHEDULED FLT DUE TO THE REPLACEMENT OF A WORN BRAKE. THE DETERMINATION WAS MADE NOT TO REPLACE THE WORN BRAKE (DUE TO DIFFICULTY IN MOUNTING THE NEW BRAKE), BUT INSTEAD TO DEACTIVATE THE WORN BRAKE AND DISPATCH THE FLT WITH A DEACTIVATED BRAKE. THERE ARE TWO METHODS OF DEACTIVATING THE BRAKES, AND BOTH METHODS INCUR SOME PERFORMANCE LIMITATIONS FOR TKOF AND ARE ADDRESSED IN THE FLT MANUAL. WHEN I CHKED THE PERFORMANCE LIMITATIONS, I ADVISED THE CAPT THAT WE WOULD BE UNABLE TO TKOF AT THE PLANNED GROSS WT WITH THE BRAKE DEACTIVATED AT THE METHOD PLANNED. THE CAPT LEFT THE COCKPIT AND DISCUSSED THE MATTER WITH DISPATCH AND MAINT FOR 20-30 MINS. WHEN HE RETURNED, HE ADVISED ME THAT DISPATCH HAD DIFFERENT PERFORMANCE NUMBERS THAN THE FLT MANUAL. WE ALSO CALLED UP TKOF PERFORMANCE NUMBERS ON THE COCKPIT DATALINK, AND THEY AGREED WITH THE DISPATCH NUMBERS. THE CAPT DECIDED TO USE THE DISPATCH/COMPUTER NUMBERS AS THE CORRECT ONES, AND THE TKOF AND FLT WERE MADE WITHOUT INCIDENT. AFTER THE TRIP PAIRING WAS COMPLETE, THE CAPT INVESTIGATED THE MATTER FURTHER WITH THE INTENT OF CORRECTING THE FLT MANUAL. DURING THE COURSE OF HIS INVESTIGATION, HE LEARNED THAT THE FLT MANUALS WERE CORRECT, THE COMPUTER GENERATED NUMBERS AND DISPATCH NUMBERS WERE WRONG. HE IS PROCEEDING WITH ACTIONS TO DISCLOSE THIS DISCREPANCY TO BOTH THE AIRLINE AND THE FAA, AND TO CORRECT THE DISPATCH AND COMPUTER PERFORMANCE NUMBERS. MY LESSON LEARNED: IF THERE IS A DISCREPANCY IN OPERATIONAL GUIDANCE FROM DIFFERENT SOURCES, EITHER POSITIVELY RESOLVE THE DISCREPANCY OR USE THE MOST CONSERVATIVE OF THE GUIDANCE. SUPPLEMENTAL INFO FROM ACN 339305: UNFORTUNATELY, IT WAS DISPATCH DATA VERSUS FLT MANUAL DATA. BASED ON THE FACT THAT WE USE SO MUCH COMPUTER GENERATED DATA DAILY (SUCH AS WT MANIFEST/TKOF DATA), THE CAPT ELECTED TO ACCEPT THE DISPATCH DATA FOR TKOF. THE RESULT OF ACCEPTING THE DISPATCH COMPUTER GENERATED TKOF WT DATA WAS TKOF AT APPROX 102500 LBS OVER MAX ALLOWABLE FOR THAT RWY.

Data retrieved from NASA's ASRS site as of July 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.