Narrative:

Just prior to dispatch, received call from flight crew that the aft cargo fire detection system had fail light on both 'a' and 'B' detector system. Controller unit showed faults on A1 and B2 detectors. Per MEL, aircraft requires 1 operable system in each cargo pit. Detectors are installed in pairs -- one in front of the other as A1-B1, A2-B2, A3-B3 (note diagram). In order to make one operable system, we swapped connectors A2 and B2. Now 'B' system was operable and aircraft was dispatched with 'a' system inoperative per MEL 26232. Aircraft maintenance controller returned aircraft to gate noting that the detectors should have been swapped -- not connectors. Resolved problem by swapping detectors A2 and B2 and redispatching aircraft. The factors leading up to this error were the vagueness of the MEL and not being aware that swapping connectors is not an allowable practice. Detector pair in question are in such close proximity that swapping connector is easily done without any stress to harnesses or connectors.

Related reports:

Google
 

Original NASA ASRS Text

Title: A B737-500 WAS DISPATCHED WITH THE AFT CARGO COMPARTMENT FIRE DETECTOR SYS 'A' DEFERRED IMPROPERLY DUE TO MEL INTERP.

Narrative: JUST PRIOR TO DISPATCH, RECEIVED CALL FROM FLC THAT THE AFT CARGO FIRE DETECTION SYS HAD FAIL LIGHT ON BOTH 'A' AND 'B' DETECTOR SYS. CONTROLLER UNIT SHOWED FAULTS ON A1 AND B2 DETECTORS. PER MEL, ACFT REQUIRES 1 OPERABLE SYS IN EACH CARGO PIT. DETECTORS ARE INSTALLED IN PAIRS -- ONE IN FRONT OF THE OTHER AS A1-B1, A2-B2, A3-B3 (NOTE DIAGRAM). IN ORDER TO MAKE ONE OPERABLE SYS, WE SWAPPED CONNECTORS A2 AND B2. NOW 'B' SYS WAS OPERABLE AND ACFT WAS DISPATCHED WITH 'A' SYS INOP PER MEL 26232. ACFT MAINT CONTROLLER RETURNED ACFT TO GATE NOTING THAT THE DETECTORS SHOULD HAVE BEEN SWAPPED -- NOT CONNECTORS. RESOLVED PROB BY SWAPPING DETECTORS A2 AND B2 AND REDISPATCHING ACFT. THE FACTORS LEADING UP TO THIS ERROR WERE THE VAGUENESS OF THE MEL AND NOT BEING AWARE THAT SWAPPING CONNECTORS IS NOT AN ALLOWABLE PRACTICE. DETECTOR PAIR IN QUESTION ARE IN SUCH CLOSE PROX THAT SWAPPING CONNECTOR IS EASILY DONE WITHOUT ANY STRESS TO HARNESSES OR CONNECTORS.

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.