B737-300 FLT CREW IN CRUISE AT FL290; MADE AN EMER DSCNT AND DIVERTED DUE TO AN ALT WARNING HORN AND CAB ALT CLIMBING TO 14000 FT.

Narrative

CRUISE FL290 FROM XXX-XXX THE ALT WARNING HORN SOUNDED AND CABIN ALT READ 10500 FT AND INCREASING. OXYGEN MASKS WERE PUT ON AND CHKLIST RUN. CABIN ALT WAS APCHING 14000 FT; SO I TURNED ON PAX OXYGEN; EMER DECLARED AND DSCNT BEGUN. EMER WAS DECLARED TO ENSURE TFC SEPARATION ON DSCNT. NO ACFT WERE IN OUR VICINITY ON DSCNT. THE DEPRESSURIZATION WAS GRADUAL AND WAS NOT FELT (EARS OR HYPOXIA SYMPTOMS). FLT ATTENDANTS INITIALLY THOUGHT OXYGEN MASKS DROPPING WAS INADVERTENT; BUT I INFORMED THEM TO USE THE MASKS AFTER LEVELING AT 10000 FT; IT APPEARED WE GAINED CTL OF THE CABIN PRESSURIZATION. DISPATCH WAS VERY DIFFICULT TO PATCH THROUGH COMPANY RADIO. THEY SAID TO PROCEED TO MHT. EMER DSCNT WAS SMOOTH AND CTLED. LNDG WAS UNEVENTFUL AND THERE WERE NO INJURIES OR COMPLAINTS FROM CUSTOMERS. THE REASON FOR FILING THIS RPT WAS IN CASE ATC HAD ANY PROBS OR COMPLAINTS WITH US ASKING FOR THE EMER DSCNT OF WHICH NONE WERE STATED DURING THE EVENT. CREW OVERNIGHTED IN MHT AS SCHEDULED AND NO CAUSE FOR THE DEPRESSURIZATION HAD BEEN DETERMINED WHEN WE LEFT FOR THE HOTEL.