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B747-200 is dispatched with two of three packs deferred inoperative. Climbing through FL300 cabin altitude warning sounds and aircraft must descend to maintain a cabin altitude below 10K.
| Attributes | |
| ACN | 801375 |
| Time | |
| Date | 200808 |
| Place | |
| Locale Reference | airport : zzz.airport |
| State Reference | US |
| Altitude | msl single value : 30000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Night |
| Aircraft 1 | |
| Controlling Facilities | artcc : zzz.artcc tower : iad.tower |
| Operator | common carrier : air carrier |
| Make Model Name | B747-200 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | cruise : level |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Qualification | pilot : flight engineer |
| Experience | flight time last 90 days : 120 flight time total : 20000 flight time type : 120 |
| ASRS Report | 801375 |
| Events | |
| Anomaly | aircraft equipment problem : critical non adherence : far non adherence : published procedure |
| Independent Detector | aircraft equipment other aircraft equipment : cabin alt wng |
| Resolutory Action | flight crew : exited adverse environment |
| Supplementary | |
| Problem Areas | Maintenance Human Performance Aircraft Company Flight Crew Human Performance |
| Primary Problem | Company |
Narrative:
Aircraft is a 3 pack aircraft and 2 packs were deferred. Crew and I referred to MEL and disagreed with maintenance deferral number. In the MEL right below the category that they had used was a bold type heading that said 3 pack aircraft; then 3 installed 2 required for dispatch. Maintenance stated that because the previous category did not list a total number of packs installed but only required 1 for dispatch and we were good to go. We called our management pilot on duty and he agreed with the maintenance interpretation of the MEL so my crew and I agreed to go. Upon reaching FL300 the cabin altitude kept climbing above 10000 ft so we initiated a descent down to FL200 which is where we were able to get the cabin altitude to 9800 ft and not wear oxygen masks. The frustration with the incident is that my crew and I were told we were reading the MEL wrong when we applied it as we have been doing for 20 yrs and is a 3 pack aircraft really able to run on 1 pack?
Original NASA ASRS Text
Title: B747-200 IS DISPATCHED WITH TWO OF THREE PACKS DEFERRED INOPERATIVE. CLIMBING THROUGH FL300 CABIN ALT WARNING SOUNDS AND ACFT MUST DESCEND TO MAINTAIN A CABIN ALT BELOW 10K.
Narrative: ACFT IS A 3 PACK ACFT AND 2 PACKS WERE DEFERRED. CREW AND I REFERRED TO MEL AND DISAGREED WITH MAINT DEFERRAL NUMBER. IN THE MEL RIGHT BELOW THE CATEGORY THAT THEY HAD USED WAS A BOLD TYPE HEADING THAT SAID 3 PACK ACFT; THEN 3 INSTALLED 2 REQUIRED FOR DISPATCH. MAINT STATED THAT BECAUSE THE PREVIOUS CATEGORY DID NOT LIST A TOTAL NUMBER OF PACKS INSTALLED BUT ONLY REQUIRED 1 FOR DISPATCH AND WE WERE GOOD TO GO. WE CALLED OUR MGMNT PLT ON DUTY AND HE AGREED WITH THE MAINTENANCE INTERP OF THE MEL SO MY CREW AND I AGREED TO GO. UPON REACHING FL300 THE CABIN ALT KEPT CLBING ABOVE 10000 FT SO WE INITIATED A DSCNT DOWN TO FL200 WHICH IS WHERE WE WERE ABLE TO GET THE CABIN ALT TO 9800 FT AND NOT WEAR OXYGEN MASKS. THE FRUSTRATION WITH THE INCIDENT IS THAT MY CREW AND I WERE TOLD WE WERE READING THE MEL WRONG WHEN WE APPLIED IT AS WE HAVE BEEN DOING FOR 20 YRS AND IS A 3 PACK ACFT REALLY ABLE TO RUN ON 1 PACK?
Data retrieved from NASA's ASRS site as of May 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.