Narrative:

Removed an APU from a B737-300. Turned over installation to midnight shift and counted on the serviceable removable/installation tag provided with the APU to be good; when in fact; the tag belonged to a different APU. So what ended up happening was that an unserviceable APU was installed and the aircraft was returned to service.

Google
 

Original NASA ASRS Text

Title: Two mechanics report on their involvement with the installation of an unserviceable APU into a B737-300.

Narrative: Removed an APU from a B737-300. Turned over installation to midnight shift and counted on the serviceable removable/installation tag provided with the APU to be good; when in fact; the tag belonged to a different APU. So what ended up happening was that an unserviceable APU was installed and the aircraft was returned to service.

Data retrieved from NASA's ASRS site as of April 2012 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.