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Flight crew of a B727 started a descent when noticing that the cabin altitude was rising above normal. Descent request was made to ATC as they were making their descent. The cabin pressure held at a lower altitude and they continued to destination. Maintenance found that the reason that a higher altitude could not be maintained was 1 pressurization pack was not working.
| Attributes | |
| ACN | 407235 |
| Time | |
| Date | 199806 |
| Day | Sat |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | atc facility : mdt |
| State Reference | PA |
| Altitude | msl bound lower : 20000 msl bound upper : 25000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zny |
| Operator | common carrier : air carrier |
| Make Model Name | Large Transport, Low Wing, 3 Turbojet Eng |
| Flight Phase | climbout : intermediate altitude |
| Route In Use | enroute airway : zny |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Experience | flight time total : 10000 flight time type : 800 |
| ASRS Report | 407235 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : atp pilot : flight engineer |
| Experience | flight time last 90 days : 200 flight time total : 9100 flight time type : 800 |
| ASRS Report | 406583 |
| Events | |
| Anomaly | aircraft equipment problem : critical altitude deviation : excursion from assigned altitude other anomaly other |
| Independent Detector | aircraft equipment other aircraft equipment : unspecified other flight crewa |
| Resolutory Action | other |
| Consequence | Other |
| Supplementary | |
| Primary Problem | Aircraft |
| Air Traffic Incident | Pilot Deviation |
Narrative:
During climb to FL350, experienced cabin depressurization at FL250. Leveloff was made at FL250 to stop cabin from climbing above 10500 ft cabin altitude. While requesting clearance to FL200, descent was initiated. ATC granted descent. No traffic separation loss was experienced. No traffic observed on TCASII during descent. Supplemental information from acn 406583: during the climb, while passing 10000 ft, our flight engineer remarked that he could not control the air mix valve on our right air conditioning pack. Since duct pressures and pack operating temperatures seemed normal, we assumed a position indicator failure. When a pack is not operating, the air mix valves drive full cold, which is where this one was. We would later learn from maintenance that the pack was not operating at all, and the remaining one was not sufficient to pressurize the airplane.
Original NASA ASRS Text
Title: FLC OF A B727 STARTED A DSCNT WHEN NOTICING THAT THE CABIN ALT WAS RISING ABOVE NORMAL. DSCNT REQUEST WAS MADE TO ATC AS THEY WERE MAKING THEIR DSCNT. THE CABIN PRESSURE HELD AT A LOWER ALT AND THEY CONTINUED TO DEST. MAINT FOUND THAT THE REASON THAT A HIGHER ALT COULD NOT BE MAINTAINED WAS 1 PRESSURIZATION PACK WAS NOT WORKING.
Narrative: DURING CLB TO FL350, EXPERIENCED CABIN DEPRESSURIZATION AT FL250. LEVELOFF WAS MADE AT FL250 TO STOP CABIN FROM CLBING ABOVE 10500 FT CABIN ALT. WHILE REQUESTING CLRNC TO FL200, DSCNT WAS INITIATED. ATC GRANTED DSCNT. NO TFC SEPARATION LOSS WAS EXPERIENCED. NO TFC OBSERVED ON TCASII DURING DSCNT. SUPPLEMENTAL INFO FROM ACN 406583: DURING THE CLB, WHILE PASSING 10000 FT, OUR FE REMARKED THAT HE COULD NOT CTL THE AIR MIX VALVE ON OUR R AIR CONDITIONING PACK. SINCE DUCT PRESSURES AND PACK OPERATING TEMPS SEEMED NORMAL, WE ASSUMED A POS INDICATOR FAILURE. WHEN A PACK IS NOT OPERATING, THE AIR MIX VALVES DRIVE FULL COLD, WHICH IS WHERE THIS ONE WAS. WE WOULD LATER LEARN FROM MAINT THAT THE PACK WAS NOT OPERATING AT ALL, AND THE REMAINING ONE WAS NOT SUFFICIENT TO PRESSURIZE THE AIRPLANE.
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.