Narrative:

As lead mechanic on my shift I was at the gate to assist the assigned mechanic in troubleshooting a reported intermittent flickering 'dc fail' light which was reported by the flight deck crew. My co-worker mechanic entered the flight deck and debriefed the crew about the discrepancy which was subsequently reported to me verbally as the #2 IRU 'dc fail' light flickering on intermittently in cruise flight. The captain reported to me verbally in the jetway that all other cockpit instruments appeared normal. The flickering eventually stopped and no other indications of a problem with any other system were noted. At the gate we were unable to duplicate any problem with either IRU system. With the assistance of 2 fellow mechanics and phone consultation with a technical supervisor we examined the wiring diagram and determined that 2 likely causes for this discrepancy would be the IRU and the integrated flight accessory unit. We removed and replaced both of these components per the maintenance manual and conducted CAT III recertification with no other discrepancies noted. I entered the corrected action in the logbook and the aircraft departed normally. Just before shift change at XA45 the duty line maintenance supervisor brought to my attention that the corrective action I had entered in the logbook did not agree with the discrepancy entered by the captain. The log discrepancy indicated that the problem was with the #1 IRU. I contacted the mechanic who had entered the flight deck and debriefed the crew to verify which IRU the crew had indicated to him was discrepant. He reaffirmed to me that it was the #2 IRU. At that point I figured that the captain had entered the wrong IRU position in his logbook write-up. Per the maintenance procedures manual; I corrected the discrepancy to indicate that the #2 IRU was the discrepant system. After further thought and a second review of the related maintenance history for aircraft; I felt it prudent to track down the captain who had entered the discrepancy to verify with him which IRU system he had intended to write up. I contacted flight operations to have the captain located and a message relayed to him to contact me as soon as possible. The captain called me at my home at XD10. He indicated to me that he had entered the discrepancy into the logbook as the problem being with the #1 IRU. Apparently there had been some confusion during the cockpit debrief with my co-worker. My co-worker mistakenly reported to me that the problem was with the #2 IRU. I contacted the line maintenance supervisor. We determined that aircraft was already en route on a regularly scheduled flight. The evening shift was instructed to meet the aircraft upon arrival and determine if there had been any further problems with the #1 IRU system and conduct further troubleshooting as required to verify proper operation of the #1 IRU. The logbook page was corrected accordingly to reflect the captain's original write-up as being with the #1 IRU. Action to prevent further occurrences: read logbook written discrepancy regardless of what information is verbally communicated to me by involved individuals.

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Original NASA ASRS Text

Title: A B737-300 WAS DISPATCHED WITH #2 IRU AND THE #2 ACCESSORY UNIT REPLACED AND AUTOLAND CHK OK. LOG RPT WAS #1 INERTIAL REF 'DC' FAIL.

Narrative: AS LEAD MECH ON MY SHIFT I WAS AT THE GATE TO ASSIST THE ASSIGNED MECH IN TROUBLESHOOTING A RPTED INTERMITTENT FLICKERING 'DC FAIL' LIGHT WHICH WAS RPTED BY THE FLT DECK CREW. MY CO-WORKER MECH ENTERED THE FLT DECK AND DEBRIEFED THE CREW ABOUT THE DISCREPANCY WHICH WAS SUBSEQUENTLY RPTED TO ME VERBALLY AS THE #2 IRU 'DC FAIL' LIGHT FLICKERING ON INTERMITTENTLY IN CRUISE FLT. THE CAPT RPTED TO ME VERBALLY IN THE JETWAY THAT ALL OTHER COCKPIT INSTS APPEARED NORMAL. THE FLICKERING EVENTUALLY STOPPED AND NO OTHER INDICATIONS OF A PROB WITH ANY OTHER SYS WERE NOTED. AT THE GATE WE WERE UNABLE TO DUPLICATE ANY PROB WITH EITHER IRU SYS. WITH THE ASSISTANCE OF 2 FELLOW MECHS AND PHONE CONSULTATION WITH A TECHNICAL SUPVR WE EXAMINED THE WIRING DIAGRAM AND DETERMINED THAT 2 LIKELY CAUSES FOR THIS DISCREPANCY WOULD BE THE IRU AND THE INTEGRATED FLT ACCESSORY UNIT. WE REMOVED AND REPLACED BOTH OF THESE COMPONENTS PER THE MAINT MANUAL AND CONDUCTED CAT III RECERTIFICATION WITH NO OTHER DISCREPANCIES NOTED. I ENTERED THE CORRECTED ACTION IN THE LOGBOOK AND THE ACFT DEPARTED NORMALLY. JUST BEFORE SHIFT CHANGE AT XA45 THE DUTY LINE MAINT SUPVR BROUGHT TO MY ATTN THAT THE CORRECTIVE ACTION I HAD ENTERED IN THE LOGBOOK DID NOT AGREE WITH THE DISCREPANCY ENTERED BY THE CAPT. THE LOG DISCREPANCY INDICATED THAT THE PROB WAS WITH THE #1 IRU. I CONTACTED THE MECH WHO HAD ENTERED THE FLT DECK AND DEBRIEFED THE CREW TO VERIFY WHICH IRU THE CREW HAD INDICATED TO HIM WAS DISCREPANT. HE REAFFIRMED TO ME THAT IT WAS THE #2 IRU. AT THAT POINT I FIGURED THAT THE CAPT HAD ENTERED THE WRONG IRU POS IN HIS LOGBOOK WRITE-UP. PER THE MAINT PROCS MANUAL; I CORRECTED THE DISCREPANCY TO INDICATE THAT THE #2 IRU WAS THE DISCREPANT SYS. AFTER FURTHER THOUGHT AND A SECOND REVIEW OF THE RELATED MAINT HISTORY FOR ACFT; I FELT IT PRUDENT TO TRACK DOWN THE CAPT WHO HAD ENTERED THE DISCREPANCY TO VERIFY WITH HIM WHICH IRU SYS HE HAD INTENDED TO WRITE UP. I CONTACTED FLT OPS TO HAVE THE CAPT LOCATED AND A MESSAGE RELAYED TO HIM TO CONTACT ME ASAP. THE CAPT CALLED ME AT MY HOME AT XD10. HE INDICATED TO ME THAT HE HAD ENTERED THE DISCREPANCY INTO THE LOGBOOK AS THE PROB BEING WITH THE #1 IRU. APPARENTLY THERE HAD BEEN SOME CONFUSION DURING THE COCKPIT DEBRIEF WITH MY CO-WORKER. MY CO-WORKER MISTAKENLY RPTED TO ME THAT THE PROB WAS WITH THE #2 IRU. I CONTACTED THE LINE MAINT SUPVR. WE DETERMINED THAT ACFT WAS ALREADY ENRTE ON A REGULARLY SCHEDULED FLT. THE EVENING SHIFT WAS INSTRUCTED TO MEET THE ACFT UPON ARR AND DETERMINE IF THERE HAD BEEN ANY FURTHER PROBS WITH THE #1 IRU SYS AND CONDUCT FURTHER TROUBLESHOOTING AS REQUIRED TO VERIFY PROPER OP OF THE #1 IRU. THE LOGBOOK PAGE WAS CORRECTED ACCORDINGLY TO REFLECT THE CAPT'S ORIGINAL WRITE-UP AS BEING WITH THE #1 IRU. ACTION TO PREVENT FURTHER OCCURRENCES: READ LOGBOOK WRITTEN DISCREPANCY REGARDLESS OF WHAT INFO IS VERBALLY COMMUNICATED TO ME BY INVOLVED INDIVIDUALS.

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.