B737-800
Flight Crew Air Transport Pilot (ATP)
Human-Machine Interface
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Overcame Equipment Problem
Aircraft; Human Factors
During climb; the cabin altitude warning horn activated passing approximately; 11;000 FT. First Officer (pilot flying) immediately donned O2 mask and leveled aircraft at 11;000 FT (with ATC permission). We quickly recognized that our problem was that both packs were off. 'Cabin Altitude Warning' procedures were stopped and one pack was reinstated. After pressurization stabilized; the second pack was reinstated and normal operations resumed. The remainder of flight was uneventful. The aircraft had overnighted in ORD. I believe the pack switches may have been off when we arrived at the aircraft. A contributing factor to the crew's missing the incorrect position of the pack switches was the mild outside temperature and neither heating nor cooling were required before takeoff.
[No substantive additional information was contained in the Secondary Report narrative.]
When the flight crew of a B737-800 failed to note both pack switches were off prior to takeoff they predictably received a Cabin Altitude Warning during the climb. They leveled off; turned the packs back on one at a time; and continued the flight.