Date: 201305
Local time of day: 1801-2400
Location: ZZZ.ARTCC, US
Flight conditions: IMC
Weather elements / visibility: 1
Light: Daylight
Aircraft: B737-300
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Pressurization System
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion; Human-Machine Interface
Second reporter function: First Officer; Pilot Not Flying
Anomaly: ATC Issue All Types; Aircraft Equipment Problem Critical; Deviation - Altitude Excursion From Assigned Altitude
Detector: Automation Aircraft Other Automation
When detected: In-flight
Result: General Declared Emergency
Contributing factors: Procedure; Aircraft; Human Factors
Primary problem: Aircraft

Narrative: While at cruise in IMC at FL370 the Cabin Altitude Warning horn and Cabin Altitude Warning light came on. We immediately donned our oxygen masks and; as the pilot flying; I began an emergency descent to 10;000 feet. I declared an emergency with ATC and; during the descent; we got a slight vector for traffic. The pressurization panel was in normal configuration (Bleeds ON; Packs ON; FLT/GND switch in FLT.) The cabin altitude was above 10;000 feet and slowly climbing. The cabin altitude never got above about 12;500 feet and the passenger masks did not deploy. The First Officer ran the Cabin Altitude Warning Horn and Emergency Descent Checklists. I notified the flight attendants and the passengers. Passing about 18;000 MSL the pressurization panel AUTO FAIL and STBY lights came on. The First Officer ran that checklist as well and placed the mode control switch to STBY. After leveling off at 10;000 feet the Cabin Altitude Warning horn silenced after a minute or so and we then notified Dispatch via ACARS. We were cleared direct to our destination airport and flew uneventfully to landing. On the ground; I contacted Dispatch; Maintenance; and Flight Operations; [and] then made a logbook entry. The flight attendants said no passengers seemed to have any issues except maybe a few ear pops. It took a long ten seconds to establish communications between myself and the First Officer. On donning the oxygen mask; I knocked my glasses and headset off. I also had an issue with the pressurization gauge; during descent; both arms overlapped so I couldn't easily see the smaller arm and read the cabin pressurization. The larger arm (differential pressure) covered up the smaller arm below it. Both were at the four to five o'clock position on the gauge. This is a concern because I wasn't able to easily see if we were going to hit a cabin altitude of 14;000 feet (and get the masks dropping.)


Second narrative: No additional information was contained in the secondary narrative.


Synopsis: A B737-300 flight crew suffered pressurization failure at FL370; initiated an emergency descent and descended to 10;000 feet where they continued to destination. Maximum cabin altitude reached was approximately 12;500 feet and passenger O2 masks did not deploy.