Narrative:

Climbing through FL210 we received a warning horn (intermittent) followed by warning light - cabin altitude. Analog pressurization controller panel; amber 'auto fail light' illuminated. Cabin altimeter/differential pressure indicator showed cabin at 3;500 ft and rapidly increasing. No other master caution lights; no dual bleed; pack trip off; wing-body overheat; or bleed trip off lights. Simultaneously; [we advised ATC]; a turn to the left was made (off of the SID) and descent was initiated. The crew O2 masks were put on and crew communication was established; qrc/QRH checklists were performed.in the descent; with cabin stabilized at about 13;000 ft; flight attendants were briefed: 'stable airplane; rapid depressurization event; returning to [departure airport]. Secure the cabin for arrival.' same message passed to passengers level at 10;000 ft. All non-normal items were rechecked; complete. Also; word was passed to operations via radio to inform of our return; asked operations notify dispatch; maintenance control; and maintenance.passengers O2 masks did not auto deploy; as we did not exceed a cabin altitude of 14;000 ft. I made the decision to not manually deploy passenger O2 masks. Pm/first officer agreed with the decision to not manually deploy passenger O2 masks. Decision to not deploy passenger O2 masks was made under captain's emergency authority. Pm/first officer handled all qrc and QRH checklists and communicated with ATC. (And; I must add; performed flawlessly all duties throughout the entire non-normal event.) reviews were made by pm of all non-normal checklists to ensure items were not missed and all checklists were properly complied with; outstanding work by this first officer. Flight attendants also performed with equal excellence and professionalism. Fire department inspected aircraft clear of runway [and] we proceeded to [the] gate. Support from base; operations; ground; and maintenance was phenomenal. Operations were under great pressure to handle our passengers. 30 passengers were rerouted and over 100 made the trip to [destination] with us in our replacement aircraft. I'm really proud of everyone and our company. We received terrific support from operations; chief pilot; and dispatch. Overall; a great day.

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Original NASA ASRS Text

Title: B737 flight crew reported returning to departure airport after experiencing loss of cabin pressure.

Narrative: Climbing through FL210 we received a Warning Horn (Intermittent) followed by Warning Light - Cabin Altitude. Analog Pressurization Controller Panel; Amber 'Auto Fail Light' illuminated. Cabin Altimeter/Differential Pressure Indicator showed Cabin at 3;500 FT and rapidly increasing. No other Master Caution Lights; no DUAL BLEED; PACK TRIP OFF; WING-BODY OVERHEAT; or BLEED TRIP OFF lights. Simultaneously; [we advised ATC]; a turn to the left was made (off of the SID) and descent was initiated. The Crew O2 masks were put on and Crew communication was established; QRC/QRH checklists were performed.In the descent; with cabin stabilized at about 13;000 FT; Flight Attendants were briefed: 'STABLE airplane; rapid depressurization event; returning to [departure airport]. SECURE THE CABIN for arrival.' Same message passed to passengers level at 10;000 FT. All non-normal items were rechecked; complete. Also; word was passed to OPS via radio to inform of our return; asked OPS notify Dispatch; Maintenance Control; and Maintenance.Passengers O2 Masks did not auto deploy; as we did not exceed a cabin altitude of 14;000 FT. I made the decision to not manually deploy PAX O2 Masks. PM/First Officer agreed with the decision to not manually deploy PAX O2 Masks. Decision to not deploy passenger O2 Masks was made under Captain's Emergency Authority. PM/First Officer handled all QRC and QRH Checklists and communicated with ATC. (And; I must add; performed flawlessly all duties throughout the entire non-normal event.) Reviews were made by PM of all non-normal checklists to ensure items were not missed and all checklists were properly complied with; outstanding work by this First Officer. Flight Attendants also performed with equal excellence and professionalism. Fire Department inspected aircraft clear of runway [and] we proceeded to [the] gate. Support from Base; OPS; Ground; and Maintenance was phenomenal. OPS were under great pressure to handle our Passengers. 30 Passengers were rerouted and over 100 made the trip to [destination] with us in our replacement aircraft. I'm really proud of everyone and our Company. We received terrific support from Operations; Chief Pilot; and Dispatch. Overall; a great day.

Data retrieved from NASA's ASRS site 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.