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37000 Feet | Browse and search NASA's Aviation Safety Reporting System |
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DC9-30 has to make a rapid descent due to difficulty in maintaining cabin pressure while at FL350. Ok at FL280 with power kept up. Created some problem for the flight crew's approach into memphis. Postflt found a loose air conditioning bleed duct line.
| Attributes | |
| ACN | 379516 |
| Time | |
| Date | 199709 |
| Day | Sun |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | atc facility : bwg |
| State Reference | KY |
| Altitude | msl bound lower : 28000 msl bound upper : 35000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zid |
| Operator | common carrier : air carrier |
| Make Model Name | DC-9 30 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | cruise other descent other other |
| Route In Use | enroute : on vectors enroute other |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : cfi pilot : commercial pilot : flight engineer pilot : instrument pilot : atp |
| Experience | flight time last 90 days : 180 flight time total : 10000 flight time type : 3000 |
| ASRS Report | 379516 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : instrument pilot : commercial |
| Events | |
| Anomaly | aircraft equipment problem : critical other anomaly other |
| Independent Detector | aircraft equipment other aircraft equipment : unspecified |
| Resolutory Action | flight crew : declared emergency flight crew : exited adverse environment other |
| Consequence | Other |
| Supplementary | |
| Primary Problem | Aircraft |
Narrative:
Aircraft had history of pressurization problems going back several days. On climb out we found that the right pack began to cycle on and off. At cruise we also found that we had no control of the right temperature control valve either in manual or automatic. We called maintenance control on the radio telling them that we would be squawking the aircraft in memphis and describing the exact symptoms. The cabin altitude was fluctuating slightly at this point but was holding a 7500-8000 ft cabin altitude. Shortly after this, the cabin began climbing at 1000-1500 FPM and all our attempts to control it were in vain. We called ZID and requested lower altitude immediately and started a fairly rapid descent at that time with their consent. We were given FL330 initially but told them we needed lower and took a vector off course to go down to FL280 where we were able to control the cabin again. During descent to mem airport we needed to keep 1.6 EPR on both engines to keep cabin coming down and took several vectors to enable us to keep power and speed up. Mechanics found bleed duct pipe free and flopping around causing intermittent loss of air to pressure regulator valve which caused valve to open and close.
Original NASA ASRS Text
Title: DC9-30 HAS TO MAKE A RAPID DSCNT DUE TO DIFFICULTY IN MAINTAINING CABIN PRESSURE WHILE AT FL350. OK AT FL280 WITH PWR KEPT UP. CREATED SOME PROB FOR THE FLC'S APCH INTO MEMPHIS. POSTFLT FOUND A LOOSE AIR CONDITIONING BLEED DUCT LINE.
Narrative: ACFT HAD HISTORY OF PRESSURIZATION PROBS GOING BACK SEVERAL DAYS. ON CLBOUT WE FOUND THAT THE R PACK BEGAN TO CYCLE ON AND OFF. AT CRUISE WE ALSO FOUND THAT WE HAD NO CTL OF THE R TEMP CTL VALVE EITHER IN MANUAL OR AUTO. WE CALLED MAINT CTL ON THE RADIO TELLING THEM THAT WE WOULD BE SQUAWKING THE ACFT IN MEMPHIS AND DESCRIBING THE EXACT SYMPTOMS. THE CABIN ALT WAS FLUCTUATING SLIGHTLY AT THIS POINT BUT WAS HOLDING A 7500-8000 FT CABIN ALT. SHORTLY AFTER THIS, THE CABIN BEGAN CLBING AT 1000-1500 FPM AND ALL OUR ATTEMPTS TO CTL IT WERE IN VAIN. WE CALLED ZID AND REQUESTED LOWER ALT IMMEDIATELY AND STARTED A FAIRLY RAPID DSCNT AT THAT TIME WITH THEIR CONSENT. WE WERE GIVEN FL330 INITIALLY BUT TOLD THEM WE NEEDED LOWER AND TOOK A VECTOR OFF COURSE TO GO DOWN TO FL280 WHERE WE WERE ABLE TO CTL THE CABIN AGAIN. DURING DSCNT TO MEM ARPT WE NEEDED TO KEEP 1.6 EPR ON BOTH ENGS TO KEEP CABIN COMING DOWN AND TOOK SEVERAL VECTORS TO ENABLE US TO KEEP PWR AND SPD UP. MECHS FOUND BLEED DUCT PIPE FREE AND FLOPPING AROUND CAUSING INTERMITTENT LOSS OF AIR TO PRESSURE REGULATOR VALVE WHICH CAUSED VALVE TO OPEN AND CLOSE.
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.