Narrative:

During cruise flight, on 2ND leg, after approximately 37 mins at FL350, all aircraft system normal until that time. Cabin altitude warning horn came on steady. Only normal cockpit indications noted were cabin pressure altitude gauge reading 10000 ft. Immediate action procedures were accomplished (oxygen masks on, communication established), qrc items completed by the first officer. Due to the unknown nature of this cabin altitude warning, clearance from ZID was obtained to 10000 ft, emergency was declared, and diversion clearance to ind was obtained. Cabin altitude was eventually controled. No passenger oxygen mask were deployed, since cabin pressure was kept below 10500 ft. No injuries occurred, and a normal landing was made at ind. Taxi normal to gate where crash fire rescue equipment team was briefed and no further assistance required.

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Original NASA ASRS Text

Title: A B733 CAPT RPTED THAT HE DECLARED AN EMER AND DIVERTED TO IND AFTER THE CABIN ATTITUDE HORN SOUNDED.

Narrative: DURING CRUISE FLT, ON 2ND LEG, AFTER APPROX 37 MINS AT FL350, ALL ACFT SYS NORMAL UNTIL THAT TIME. CABIN ALT WARNING HORN CAME ON STEADY. ONLY NORMAL COCKPIT INDICATIONS NOTED WERE CABIN PRESSURE ALT GAUGE READING 10000 FT. IMMEDIATE ACTION PROCS WERE ACCOMPLISHED (OXYGEN MASKS ON, COM ESTABLISHED), QRC ITEMS COMPLETED BY THE FO. DUE TO THE UNKNOWN NATURE OF THIS CABIN ALT WARNING, CLRNC FROM ZID WAS OBTAINED TO 10000 FT, EMER WAS DECLARED, AND DIVERSION CLRNC TO IND WAS OBTAINED. CABIN ALT WAS EVENTUALLY CTLED. NO PAX OXYGEN MASK WERE DEPLOYED, SINCE CABIN PRESSURE WAS KEPT BELOW 10500 FT. NO INJURIES OCCURRED, AND A NORMAL LNDG WAS MADE AT IND. TAXI NORMAL TO GATE WHERE CFR TEAM WAS BRIEFED AND NO FURTHER ASSISTANCE REQUIRED.

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.