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2 pressurization switches unknowingly placed into an off position create the need for an emergency descent to 12000 ft when the MD80 flight loses its cabin pressure on frequency with ZKC.
| Attributes | |
| ACN | 633636 |
| Time | |
| Date | 200410 |
| Day | Mon |
| Local Time Of Day | 1801 To 2400 |
| Place | |
| Locale Reference | atc facility : zkc.artcc |
| State Reference | MO |
| Altitude | msl bound lower : 12000 msl bound upper : 24000 |
| Environment | |
| Weather Elements | Rain |
| Light | Night |
| Aircraft 1 | |
| Controlling Facilities | artcc : zkc.artcc tower : mmu.tower |
| Operator | common carrier : air carrier |
| Make Model Name | MD-80 Series (DC-9-80) Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Flight Phase | cruise : level |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| ASRS Report | 633636 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Events | |
| Anomaly | aircraft equipment problem : critical non adherence : company policies non adherence : published procedure non adherence : far other anomaly other |
| Independent Detector | aircraft equipment other aircraft equipment : horn lo flo light, alt light other flight crewa other flight crewb |
| Resolutory Action | flight crew : overcame equipment problem other |
| Consequence | other |
| Supplementary | |
| Problem Areas | Aircraft Flight Crew Human Performance Chart Or Publication |
| Primary Problem | Flight Crew Human Performance |
Narrative:
Level at FL240 with clearance to 12000 ft, the aircraft's flow light was noticed on. PNF, PIC, looking up 'flow light on' checklist when red cabin altitude light came on with horn. Completed red box items including rapid descent to 12000 ft and passenger oxygen mask deployment. PNF reviewed checklist for cabin altitude warning and in the expanded checklist was 'check that both air conditioning supply switches are in automatic.' PNF found both switches in the 'off' position. Speculate that after writing up several items in the logbook, just prior to descent, that when the first officer pulled the logbook off the aircraft's dashboard, it hit the 2 AC switches to the 'off' position. A one in a million shot, but that is the only reasonable explanation we can come up with. We were not changing any other switch position and had no other unusual conditions in the cockpit.
Original NASA ASRS Text
Title: 2 PRESSURIZATION SWITCHES UNKNOWINGLY PLACED INTO AN OFF POS CREATE THE NEED FOR AN EMER DSCNT TO 12000 FT WHEN THE MD80 FLT LOSES ITS CABIN PRESSURE ON FREQ WITH ZKC.
Narrative: LEVEL AT FL240 WITH CLRNC TO 12000 FT, THE ACFT'S FLOW LIGHT WAS NOTICED ON. PNF, PIC, LOOKING UP 'FLOW LIGHT ON' CHKLIST WHEN RED CABIN ALT LIGHT CAME ON WITH HORN. COMPLETED RED BOX ITEMS INCLUDING RAPID DSCNT TO 12000 FT AND PAX OXYGEN MASK DEPLOYMENT. PNF REVIEWED CHKLIST FOR CABIN ALT WARNING AND IN THE EXPANDED CHKLIST WAS 'CHK THAT BOTH AIR CONDITIONING SUPPLY SWITCHES ARE IN AUTO.' PNF FOUND BOTH SWITCHES IN THE 'OFF' POS. SPECULATE THAT AFTER WRITING UP SEVERAL ITEMS IN THE LOGBOOK, JUST PRIOR TO DSCNT, THAT WHEN THE FO PULLED THE LOGBOOK OFF THE ACFT'S DASHBOARD, IT HIT THE 2 AC SWITCHES TO THE 'OFF' POS. A ONE IN A MILLION SHOT, BUT THAT IS THE ONLY REASONABLE EXPLANATION WE CAN COME UP WITH. WE WERE NOT CHANGING ANY OTHER SWITCH POS AND HAD NO OTHER UNUSUAL CONDITIONS IN THE COCKPIT.
Data retrieved from NASA's ASRS site as of July 2007 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.