Narrative:

The inspector that performed the borescope on the #2 engine of the B777 aircraft and gave me the maintenance manual reference he was using for the damage he had found during borescope inspection of #2 engine. He had an illustration of the hpc blade. This illustration had 3 zones idented on the blade (a, B, and C). With the maintenance manual reference and the digital pictures he had taken of the damage we determined that the damage was within limits and could continue in service with a reinspect borescope cycle. We have just learned that we had used the wrong reference for our damage assessment. When you reference the damage verbiage in the maintenance manual, it references figure X which gives a snapshot of the blade areas, a, B, etc. Under hpc #1 it references figure X and when you click on it you get an illustration of the blade. Under hpc #2 through #6 they give you the same reference and when you click on it you get the same illustration again. What you don't notice is that there is a sheet #1 and a sheet #2. This information is somewhat hidden. I am submitting a rfs (revision change or correction) to change sheet #2 of figure X to its own figure number, such as figure xx for hpc blades #2 through #6. The bottom line is due to this oversight we thought the damage was within limits when in fact it is not. The aircraft is scheduled in for an engine change. Supplemental information from acn 635148: I requested my supervisor submit a change to the computerized maintenance manual to prevent this error from happening again. Engineering noticed the discrepancy and scheduled an engine change.

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Original NASA ASRS Text

Title: A B777 R ENG WAS BORESCOPED AND DIGITAL PICTURE OF THE HIGH PRESSURE BLADE WAS COMPARED TO MAINT MANUAL CHART AND FOUND WITHIN LIMITS. LATER DISCOVERED BLADE OUT OF LIMITS. SHEET #2 OF CHART WAS NOT REFED.

Narrative: THE INSPECTOR THAT PERFORMED THE BORESCOPE ON THE #2 ENG OF THE B777 ACFT AND GAVE ME THE MAINT MANUAL REF HE WAS USING FOR THE DAMAGE HE HAD FOUND DURING BORESCOPE INSPECTION OF #2 ENG. HE HAD AN ILLUSTRATION OF THE HPC BLADE. THIS ILLUSTRATION HAD 3 ZONES IDENTED ON THE BLADE (A, B, AND C). WITH THE MAINT MANUAL REF AND THE DIGITAL PICTURES HE HAD TAKEN OF THE DAMAGE WE DETERMINED THAT THE DAMAGE WAS WITHIN LIMITS AND COULD CONTINUE IN SVC WITH A REINSPECT BORESCOPE CYCLE. WE HAVE JUST LEARNED THAT WE HAD USED THE WRONG REF FOR OUR DAMAGE ASSESSMENT. WHEN YOU REF THE DAMAGE VERBIAGE IN THE MAINT MANUAL, IT REFS FIGURE X WHICH GIVES A SNAPSHOT OF THE BLADE AREAS, A, B, ETC. UNDER HPC #1 IT REFS FIGURE X AND WHEN YOU CLICK ON IT YOU GET AN ILLUSTRATION OF THE BLADE. UNDER HPC #2 THROUGH #6 THEY GIVE YOU THE SAME REF AND WHEN YOU CLICK ON IT YOU GET THE SAME ILLUSTRATION AGAIN. WHAT YOU DON'T NOTICE IS THAT THERE IS A SHEET #1 AND A SHEET #2. THIS INFO IS SOMEWHAT HIDDEN. I AM SUBMITTING A RFS (REVISION CHANGE OR CORRECTION) TO CHANGE SHEET #2 OF FIGURE X TO ITS OWN FIGURE NUMBER, SUCH AS FIGURE XX FOR HPC BLADES #2 THROUGH #6. THE BOTTOM LINE IS DUE TO THIS OVERSIGHT WE THOUGHT THE DAMAGE WAS WITHIN LIMITS WHEN IN FACT IT IS NOT. THE ACFT IS SCHEDULED IN FOR AN ENG CHANGE. SUPPLEMENTAL INFO FROM ACN 635148: I REQUESTED MY SUPVR SUBMIT A CHANGE TO THE COMPUTERIZED MAINT MANUAL TO PREVENT THIS ERROR FROM HAPPENING AGAIN. ENGINEERING NOTICED THE DISCREPANCY AND SCHEDULED AN ENG CHANGE.

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.