A B737-300 was dispatched with the incorrect FMC display unit installed.

Attributes
ACN	638799
Time
Date	200410
Day	Thu
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	agl single value : 0
Environment
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Flight Phase	ground : maintenance
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	maintenance : technician
ASRS Report	638799
Person 2
Affiliation	government : faa
Function	observation : air carrier inspector other personnel other
Events
Anomaly	aircraft equipment problem : critical maintenance problem : improper documentation maintenance problem : improper maintenance non adherence : published procedure non adherence : far
Independent Detector	other other : 2
Resolutory Action	none taken : detected after the fact
Consequence	faa : investigated other other
Factors
Maintenance	contributing factor : schedule pressure performance deficiency : installation performance deficiency : logbook entry performance deficiency : non compliance with legal requirements performance deficiency : testing
Supplementary
Problem Areas	Aircraft Chart Or Publication Maintenance Human Performance
Primary Problem	Maintenance Human Performance

Narrative:

On oct/thu/04, aircraft came to the gate with a #2 ATC control panel problem. Right&right'ed controller as per maintenance manual. Then I was notified by the pilot of aircraft that #2 CDU had a problem too. I inspected the problem, noted that the clear button on the CDU was broken. I went to the parts room and inadvertently picked up the wrong part. Installed it, ran an operations check -- checked good as per maintenance manual. As of dec/thu/04, I was unsure that I had installed part mentioned until aviation safety inspector notified me in person at the maintenance hangar that I had installed the wrong CDU for aircraft X. During the short discussion, safety inspector told me not to worry about the letter of intent. I replied to safety inspector I needed to do some research because I could not recall changing a CDU during the month of nov/04. After a couple of hours of research, I found out that I had changed the wrong part back in oct/04. After reviewing this event, I discovered that this event could happen again because of the ambiguous wording of parts coding system.

Original NASA ASRS Text

Title: A B737-300 WAS DISPATCHED WITH THE INCORRECT FMC DISPLAY UNIT INSTALLED.

Narrative: ON OCT/THU/04, ACFT CAME TO THE GATE WITH A #2 ATC CTL PANEL PROB. R&R'ED CONTROLLER AS PER MAINT MANUAL. THEN I WAS NOTIFIED BY THE PLT OF ACFT THAT #2 CDU HAD A PROB TOO. I INSPECTED THE PROB, NOTED THAT THE CLR BUTTON ON THE CDU WAS BROKEN. I WENT TO THE PARTS ROOM AND INADVERTENTLY PICKED UP THE WRONG PART. INSTALLED IT, RAN AN OPS CHK -- CHKED GOOD AS PER MAINT MANUAL. AS OF DEC/THU/04, I WAS UNSURE THAT I HAD INSTALLED PART MENTIONED UNTIL AVIATION SAFETY INSPECTOR NOTIFIED ME IN PERSON AT THE MAINT HANGAR THAT I HAD INSTALLED THE WRONG CDU FOR ACFT X. DURING THE SHORT DISCUSSION, SAFETY INSPECTOR TOLD ME NOT TO WORRY ABOUT THE LETTER OF INTENT. I REPLIED TO SAFETY INSPECTOR I NEEDED TO DO SOME RESEARCH BECAUSE I COULD NOT RECALL CHANGING A CDU DURING THE MONTH OF NOV/04. AFTER A COUPLE OF HRS OF RESEARCH, I FOUND OUT THAT I HAD CHANGED THE WRONG PART BACK IN OCT/04. AFTER REVIEWING THIS EVENT, I DISCOVERED THAT THIS EVENT COULD HAPPEN AGAIN BECAUSE OF THE AMBIGUOUS WORDING OF PARTS CODING SYS.

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.