Narrative:

Aircraft arrived at gate with an altitude alerter write-up. Rather than defer it, I had some time so decided to replace the alerter. I did not find any history on this item and using the maintenance manual regulation 34-10-9 page 501 and subsequent I proceeded. This aircraft has the new electronic alerter installed (I believe there are only 2 done out of maybe over 100 aircraft). The required operational test after replacement refers and directs one to use certain steps/paragraphs depending on which system is installed. This is the first time I have encountered this new system. Using steps 3A, B, and C, I misunderstood that step 3C only applied if we were doing the non electronic system, so I had the mind set that once I did the first 2 steps, the self test of the alerter display -- that was all that applied to this system. Had I done step 3C (which I see now does apply) then I would have also discovered the light did not work. I signed it off and the aircraft flew several days. After a couple days someone deferred the system. I became aware of the cause of the light not working because the aircraft is now in for maintenance.

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Original NASA ASRS Text

Title: A DC9-30 ALT ALERTER SYS LOG RPT IS WORKED AND THE TECHNICIAN REPLACES THE ALERTER BUT FAILS TO DO ALL MAINT MANUAL TEST STEPS.

Narrative: ACFT ARRIVED AT GATE WITH AN ALT ALERTER WRITE-UP. RATHER THAN DEFER IT, I HAD SOME TIME SO DECIDED TO REPLACE THE ALERTER. I DID NOT FIND ANY HISTORY ON THIS ITEM AND USING THE MAINT MANUAL REG 34-10-9 PAGE 501 AND SUBSEQUENT I PROCEEDED. THIS ACFT HAS THE NEW ELECTRONIC ALERTER INSTALLED (I BELIEVE THERE ARE ONLY 2 DONE OUT OF MAYBE OVER 100 ACFT). THE REQUIRED OPERATIONAL TEST AFTER REPLACEMENT REFERS AND DIRECTS ONE TO USE CERTAIN STEPS/PARAGRAPHS DEPENDING ON WHICH SYS IS INSTALLED. THIS IS THE FIRST TIME I HAVE ENCOUNTERED THIS NEW SYS. USING STEPS 3A, B, AND C, I MISUNDERSTOOD THAT STEP 3C ONLY APPLIED IF WE WERE DOING THE NON ELECTRONIC SYS, SO I HAD THE MIND SET THAT ONCE I DID THE FIRST 2 STEPS, THE SELF TEST OF THE ALERTER DISPLAY -- THAT WAS ALL THAT APPLIED TO THIS SYS. HAD I DONE STEP 3C (WHICH I SEE NOW DOES APPLY) THEN I WOULD HAVE ALSO DISCOVERED THE LIGHT DID NOT WORK. I SIGNED IT OFF AND THE ACFT FLEW SEVERAL DAYS. AFTER A COUPLE DAYS SOMEONE DEFERRED THE SYS. I BECAME AWARE OF THE CAUSE OF THE LIGHT NOT WORKING BECAUSE THE ACFT IS NOW IN FOR MAINT.

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.