Narrative:

Aircraft X had a write-up for an hgs problem. Maintenance was attempting to correct the problem when it was discovered that the 'web' or l-m intercostal [structure joining ribs or circumferential frames structure HUD is mounted on] was damaged. At that time the airplane was put back together and the hgs system continued on MEL. Engineering was evaluating the situation and trying to come up with a fix and plan to accomplish it due to the time it would require. This airplane was going into a heavy check which was a good time to attempt the repairs of the intercostal. After conferring with the stc holder; it was determined that replacement of the intercostal and a re-boresight of the hgs system for proper alignment of the forward overhead mount bracket would be required. Since the B737-300 is out of production for boeing; they do not have the piece required for replacement. Therefore; we would have to manufacture this piece in order to do the repair. This is where aircraft Y comes into the picture. This was a known good airplane and it was having a 'D' check accomplished at the time. We asked our field service representatives at the manufacturer to use the web installed in aircraft Y and a guide or template to make a new web for aircraft X. Through some miscom; they removed the web from the airplane to make the new web. Doing this invalidated the alignment for aircraft Y. Now this airplane would also have to be re-boresighted. An engineering authority/authorized for deactivation of the hgs system on aircraft X and aircraft Y was required because the overhead unit had to be removed from the airplane due to no holes in the intercostal for the overhead unit mount bracket. The holes are drilled into the intercostal when the installation of the forward overhead unit mount is accomplished. Engineering generated the engineering auths to deactivate the hgs system for both airplanes and in doing so; did not input the weight and balance information on the engineering auths. This was an oversight on engineering's part to follow the procedures set forth in the engineering guidelines. These engineering auths were revised to reflect the weight and balance changes required with the de-activation of this system by nov/wed/05.

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Original NASA ASRS Text

Title: 2 B737-300 HEADS UP GUIDANCE OVERHEAT UNIT MOUNT BRACKETS WERE REMOVED FOR A STRUCTURES REPAIR. AN ENGINEERING AUTH WAS WRITTEN TO ALLOW DEFERRAL OF THE MOUNT BRACKETS. DOCUMENT DID NOT HAVE WT AND BAL DATA PER ENGINEERING GUIDELINES.

Narrative: ACFT X HAD A WRITE-UP FOR AN HGS PROB. MAINT WAS ATTEMPTING TO CORRECT THE PROB WHEN IT WAS DISCOVERED THAT THE 'WEB' OR L-M INTERCOSTAL [STRUCTURE JOINING RIBS OR CIRCUMFERENTIAL FRAMES STRUCTURE HUD IS MOUNTED ON] WAS DAMAGED. AT THAT TIME THE AIRPLANE WAS PUT BACK TOGETHER AND THE HGS SYS CONTINUED ON MEL. ENGINEERING WAS EVALUATING THE SIT AND TRYING TO COME UP WITH A FIX AND PLAN TO ACCOMPLISH IT DUE TO THE TIME IT WOULD REQUIRE. THIS AIRPLANE WAS GOING INTO A HVY CHK WHICH WAS A GOOD TIME TO ATTEMPT THE REPAIRS OF THE INTERCOSTAL. AFTER CONFERRING WITH THE STC HOLDER; IT WAS DETERMINED THAT REPLACEMENT OF THE INTERCOSTAL AND A RE-BORESIGHT OF THE HGS SYS FOR PROPER ALIGNMENT OF THE FORWARD OVERHEAD MOUNT BRACKET WOULD BE REQUIRED. SINCE THE B737-300 IS OUT OF PRODUCTION FOR BOEING; THEY DO NOT HAVE THE PIECE REQUIRED FOR REPLACEMENT. THEREFORE; WE WOULD HAVE TO MANUFACTURE THIS PIECE IN ORDER TO DO THE REPAIR. THIS IS WHERE ACFT Y COMES INTO THE PICTURE. THIS WAS A KNOWN GOOD AIRPLANE AND IT WAS HAVING A 'D' CHK ACCOMPLISHED AT THE TIME. WE ASKED OUR FIELD SVC REPRESENTATIVES AT THE MANUFACTURER TO USE THE WEB INSTALLED IN ACFT Y AND A GUIDE OR TEMPLATE TO MAKE A NEW WEB FOR ACFT X. THROUGH SOME MISCOM; THEY REMOVED THE WEB FROM THE AIRPLANE TO MAKE THE NEW WEB. DOING THIS INVALIDATED THE ALIGNMENT FOR ACFT Y. NOW THIS AIRPLANE WOULD ALSO HAVE TO BE RE-BORESIGHTED. AN ENGINEERING AUTH FOR DEACTIVATION OF THE HGS SYS ON ACFT X AND ACFT Y WAS REQUIRED BECAUSE THE OVERHEAD UNIT HAD TO BE REMOVED FROM THE AIRPLANE DUE TO NO HOLES IN THE INTERCOSTAL FOR THE OVERHEAD UNIT MOUNT BRACKET. THE HOLES ARE DRILLED INTO THE INTERCOSTAL WHEN THE INSTALLATION OF THE FORWARD OVERHEAD UNIT MOUNT IS ACCOMPLISHED. ENGINEERING GENERATED THE ENGINEERING AUTHS TO DEACTIVATE THE HGS SYS FOR BOTH AIRPLANES AND IN DOING SO; DID NOT INPUT THE WT AND BAL INFO ON THE ENGINEERING AUTHS. THIS WAS AN OVERSIGHT ON ENGINEERING'S PART TO FOLLOW THE PROCS SET FORTH IN THE ENGINEERING GUIDELINES. THESE ENGINEERING AUTHS WERE REVISED TO REFLECT THE WT AND BAL CHANGES REQUIRED WITH THE DE-ACTIVATION OF THIS SYS BY NOV/WED/05.

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