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B737-500 experiences cabin altitude warning at FL330. Track source to airfoil anti-ice in use when not needed.
| Attributes | |
| ACN | 687646 |
| Time | |
| Date | 200602 |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| Locale Reference | atc facility : czyz.artcc |
| State Reference | ON |
| Altitude | msl single value : 36000 |
| Environment | |
| Flight Conditions | VMC |
| Aircraft 1 | |
| Controlling Facilities | artcc : czyz.artcc tower : zzz.tower |
| Operator | common carrier : air carrier |
| Make Model Name | B737-500 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | cruise : level |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Experience | flight time last 90 days : 50 flight time total : 6000 flight time type : 2300 |
| ASRS Report | 687646 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Events | |
| Anomaly | aircraft equipment problem : critical non adherence : published procedure other anomaly other |
| Independent Detector | aircraft equipment other aircraft equipment : cabin alt wrong horn |
| Supplementary | |
| Problem Areas | Aircraft Flight Crew Human Performance |
| Primary Problem | Ambiguous |
Narrative:
Shortly after top of climb at FL360 the cabin altitude warning horn came on. Crew O2 and established communication and scanned pressurization. Bleed trip with no master caution. Cabin very slow climb at 10000 ft. Since we had a little time; we reset bleed per checklist. All's well; cabin began a descent. Then bleed tripped again while still on O2. Started a descent with toronto center and rechked the checklist. It said check wing anti-ice which first officer found on. Turned off and reset the bleed which stayed reset. Leveled off at FL300 uneventfully. Wing anti-ice was off for takeoff and initial climb and may have been tripped while getting up to receive crew meal at TOC. FM states that wing anti-ice can cause pressure loss above FL330. Sure enough. Used situational awareness to not initiate an emergency descent.
Original NASA ASRS Text
Title: B737-500 EXPERIENCES CABIN ALT WARNING AT FL330. TRACK SOURCE TO AIRFOIL ANTI-ICE IN USE WHEN NOT NEEDED.
Narrative: SHORTLY AFTER TOP OF CLB AT FL360 THE CABIN ALT WARNING HORN CAME ON. CREW O2 AND ESTABLISHED COM AND SCANNED PRESSURIZATION. BLEED TRIP WITH NO MASTER CAUTION. CABIN VERY SLOW CLB AT 10000 FT. SINCE WE HAD A LITTLE TIME; WE RESET BLEED PER CHKLIST. ALL'S WELL; CABIN BEGAN A DSCNT. THEN BLEED TRIPPED AGAIN WHILE STILL ON O2. STARTED A DSCNT WITH TORONTO CTR AND RECHKED THE CHKLIST. IT SAID CHK WING ANTI-ICE WHICH FO FOUND ON. TURNED OFF AND RESET THE BLEED WHICH STAYED RESET. LEVELED OFF AT FL300 UNEVENTFULLY. WING ANTI-ICE WAS OFF FOR TKOF AND INITIAL CLB AND MAY HAVE BEEN TRIPPED WHILE GETTING UP TO RECEIVE CREW MEAL AT TOC. FM STATES THAT WING ANTI-ICE CAN CAUSE PRESSURE LOSS ABOVE FL330. SURE ENOUGH. USED SITUATIONAL AWARENESS TO NOT INITIATE AN EMER DSCNT.
Data retrieved from NASA's ASRS site as of January 2009 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.