Narrative:

I went to assist 2 other mechanics and a lead mechanic on a problem with an aircraft in service at the gate. The plane loaded with passenger and crew for revenue flight and was on delay. The crew has reported inertial reference unit #1 battery failed during preflight. This aircraft has 3 ships batteries which also serve as batteries for the inertial reference unit. I measured voltage on each one of the batteries and found one of the 3 batteries' voltage was extremely low. The extremely low battery was replaced by another mechanic. I then went to the cockpit and found the battery charger was not working. There was no svcable chargers in stock. I robbed a charger from one of our layover aircraft. Another mechanic removed the bad charger and replaced it with the robbed part. The battery, battery charger and inertial reference unit operations checked normal. I then cleared the item and signed the airworthiness release. The aircraft departed and arrived at its destination. The next day I was informed the aircraft was not flying because the charger had failed again and was awaiting a charger and 3 batteries. I was also informed the batteries on this aircraft are changed as a set and not individually. I then read the maintenance manual for the battery replacement and discovered on this aircraft the batteries must be changed as a set. I think the cause of the problem was not reviewing the maintenance manual for battery replacement and stocking the batteries individually and not as a ship set. To prevent a recurrence of the problem, we then sent a letter to our foreman to get the batteries stocked as a set and not individually. I informed the 2 other mechanics and the lead mechanic, who worked on this aircraft, that the batteries on this aircraft are to be changed as a set. Also, the maintenance manual shall be used at all times even in a delay.

Related reports:

Google
 

Original NASA ASRS Text

Title: AN MD90 WAS DISPATCHED IN NON COMPLIANCE WITH 1 OF 3 INERTIAL REF UNITS BATTERIES REPLACED. MAINT MANUAL REQUIRES ALL BATTERIES TO BE REPLACED AS A SET.

Narrative: I WENT TO ASSIST 2 OTHER MECHS AND A LEAD MECH ON A PROB WITH AN ACFT IN SVC AT THE GATE. THE PLANE LOADED WITH PAX AND CREW FOR REVENUE FLT AND WAS ON DELAY. THE CREW HAS RPTED INERTIAL REF UNIT #1 BATTERY FAILED DURING PREFLT. THIS ACFT HAS 3 SHIPS BATTERIES WHICH ALSO SERVE AS BATTERIES FOR THE INERTIAL REF UNIT. I MEASURED VOLTAGE ON EACH ONE OF THE BATTERIES AND FOUND ONE OF THE 3 BATTERIES' VOLTAGE WAS EXTREMELY LOW. THE EXTREMELY LOW BATTERY WAS REPLACED BY ANOTHER MECH. I THEN WENT TO THE COCKPIT AND FOUND THE BATTERY CHARGER WAS NOT WORKING. THERE WAS NO SVCABLE CHARGERS IN STOCK. I ROBBED A CHARGER FROM ONE OF OUR LAYOVER ACFT. ANOTHER MECH REMOVED THE BAD CHARGER AND REPLACED IT WITH THE ROBBED PART. THE BATTERY, BATTERY CHARGER AND INERTIAL REF UNIT OPS CHKED NORMAL. I THEN CLRED THE ITEM AND SIGNED THE AIRWORTHINESS RELEASE. THE ACFT DEPARTED AND ARRIVED AT ITS DEST. THE NEXT DAY I WAS INFORMED THE ACFT WAS NOT FLYING BECAUSE THE CHARGER HAD FAILED AGAIN AND WAS AWAITING A CHARGER AND 3 BATTERIES. I WAS ALSO INFORMED THE BATTERIES ON THIS ACFT ARE CHANGED AS A SET AND NOT INDIVIDUALLY. I THEN READ THE MAINT MANUAL FOR THE BATTERY REPLACEMENT AND DISCOVERED ON THIS ACFT THE BATTERIES MUST BE CHANGED AS A SET. I THINK THE CAUSE OF THE PROB WAS NOT REVIEWING THE MAINT MANUAL FOR BATTERY REPLACEMENT AND STOCKING THE BATTERIES INDIVIDUALLY AND NOT AS A SHIP SET. TO PREVENT A RECURRENCE OF THE PROB, WE THEN SENT A LETTER TO OUR FOREMAN TO GET THE BATTERIES STOCKED AS A SET AND NOT INDIVIDUALLY. I INFORMED THE 2 OTHER MECHS AND THE LEAD MECH, WHO WORKED ON THIS ACFT, THAT THE BATTERIES ON THIS ACFT ARE TO BE CHANGED AS A SET. ALSO, THE MAINT MANUAL SHALL BE USED AT ALL TIMES EVEN IN A DELAY.

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.