A B727-200 had the cabin altitude warning horn deferred per the MEL. Still had intermittent horn in-flight traced to landing gear confign horn.

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Attributes
ACN	508985
Time
Date	200104
Day	Fri
Place
Locale Reference	airport : zzz.airport
State Reference	US
Aircraft 1
Controlling Facilities	artcc : zzz.artcc
Operator	common carrier : air carrier
Make Model Name	B727-200
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	508985
Person 2
Affiliation	company : air carrier
Function	other personnel
Events
Anomaly	aircraft equipment problem : critical maintenance problem : non compliance with mel maintenance problem : improper documentation maintenance problem : improper maintenance non adherence : published procedure non adherence : far
Independent Detector	aircraft equipment other aircraft equipment : configuration warn horn other flight crewa
Resolutory Action	flight crew : overcame equipment problem flight crew : overrode automation
Consequence	other other
Factors
Maintenance	contributing factor : manuals contributing factor : schedule pressure performance deficiency : fault isolation performance deficiency : non compliance with legal requirements performance deficiency : logbook entry
Supplementary
Problem Areas	Maintenance Human Performance Flight Crew Human Performance Chart Or Publication Aircraft
Primary Problem	Maintenance Human Performance

Narrative:

We were dispatched with an aircraft with a history of the intermittent warning horn going off. The altitude warning horn had been placarded inoperative as per MEL 21-17. En route, the intermittent warning horn began to sound. The horn could not be silenced using the altitude warning cut-off switch. This horn made it nearly impossible to have effective communication between crew members. I deemed that to continue to allow the horn to sound could jeopardize the safety of flight. I utilized captain's authority/authorized under far part 121.557 and company procedures and disabled the aural warning circuit breaker contrary to company bulletin. Flight landed without further incident. In retrospect, cause of the horn was not the altitude warning system but the confign warning system and the flight should have never departed. I believe maintenance was arbitrary in issuing a placard under 21-17 and had no idea of what the true source of the warning horn was. Aircraft taken OTS at destination and repaired. History shows no further occurrences.

Original NASA ASRS Text

Title: A B727-200 HAD THE CABIN ALT WARNING HORN DEFERRED PER THE MEL. STILL HAD INTERMITTENT HORN INFLT TRACED TO LNDG GEAR CONFIGN HORN.

Narrative: WE WERE DISPATCHED WITH AN ACFT WITH A HISTORY OF THE INTERMITTENT WARNING HORN GOING OFF. THE ALT WARNING HORN HAD BEEN PLACARDED INOP AS PER MEL 21-17. ENRTE, THE INTERMITTENT WARNING HORN BEGAN TO SOUND. THE HORN COULD NOT BE SILENCED USING THE ALT WARNING CUT-OFF SWITCH. THIS HORN MADE IT NEARLY IMPOSSIBLE TO HAVE EFFECTIVE COM BTWN CREW MEMBERS. I DEEMED THAT TO CONTINUE TO ALLOW THE HORN TO SOUND COULD JEOPARDIZE THE SAFETY OF FLT. I UTILIZED CAPT'S AUTH UNDER FAR PART 121.557 AND COMPANY PROCS AND DISABLED THE AURAL WARNING CIRCUIT BREAKER CONTRARY TO COMPANY BULLETIN. FLT LANDED WITHOUT FURTHER INCIDENT. IN RETROSPECT, CAUSE OF THE HORN WAS NOT THE ALT WARNING SYS BUT THE CONFIGN WARNING SYS AND THE FLT SHOULD HAVE NEVER DEPARTED. I BELIEVE MAINT WAS ARBITRARY IN ISSUING A PLACARD UNDER 21-17 AND HAD NO IDEA OF WHAT THE TRUE SOURCE OF THE WARNING HORN WAS. ACFT TAKEN OTS AT DEST AND REPAIRED. HISTORY SHOWS NO FURTHER OCCURRENCES.

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.