B757 flight crew on ferry flight report cabin altitude warning passing FL385 in descent.

Attributes
ACN	789749
Time
Date	200806
Local Time Of Day	0001 To 0600
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl single value : 38500
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Controlling Facilities	tower : zzz.tower
Operator	common carrier : air carrier
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
ASRS Report	789749
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Experience	flight time total : 8800
ASRS Report	789748
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	aircraft equipment other aircraft equipment : master warning light and horn other flight crewa other flight crewb
Resolutory Action	flight crew : declared emergency flight crew : exited adverse environment
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

Aircraft cabin altitude climbed above 10000 ft. This was not a rapid depressurization event -- aircraft did not completely depressurize -- 15000 ft highest cabin altitude reached. Also; there was no deviation from ATC clearance. B757 aircraft; empty ferry flight; FL400; right pack on; automatic 2 selector; center autoplt deferred; normal operations. VNAV on-path normal descent to 11000 ft cleared about 105 NM from OM. At about FL385; we got a master warning light and horn. The cabin altitude light was illuminated and we both sensed a hypoxic environment. We immediately donned masks; established communication and performed the recall items. The cabin altitude was about 15000 ft at the highest. All checklist procedures performed and normal landing were accomplished. Event recorded in the logbook. Crew does not know why the aircraft failed to maintain cabin altitude.

Original NASA ASRS Text

Title: B757 FLT CREW ON FERRY FLIGHT REPORT CABIN ALT WARNING PASSING FL385 IN DESCENT.

Narrative: ACFT CABIN ALT CLBED ABOVE 10000 FT. THIS WAS NOT A RAPID DEPRESSURIZATION EVENT -- ACFT DID NOT COMPLETELY DEPRESSURIZE -- 15000 FT HIGHEST CABIN ALT REACHED. ALSO; THERE WAS NO DEV FROM ATC CLRNC. B757 ACFT; EMPTY FERRY FLT; FL400; R PACK ON; AUTO 2 SELECTOR; CTR AUTOPLT DEFERRED; NORMAL OPS. VNAV ON-PATH NORMAL DSCNT TO 11000 FT CLRED ABOUT 105 NM FROM OM. AT ABOUT FL385; WE GOT A MASTER WARNING LIGHT AND HORN. THE CABIN ALT LIGHT WAS ILLUMINATED AND WE BOTH SENSED A HYPOXIC ENVIRONMENT. WE IMMEDIATELY DONNED MASKS; ESTABLISHED COM AND PERFORMED THE RECALL ITEMS. THE CABIN ALT WAS ABOUT 15000 FT AT THE HIGHEST. ALL CHKLIST PROCS PERFORMED AND NORMAL LNDG WERE ACCOMPLISHED. EVENT RECORDED IN THE LOGBOOK. CREW DOES NOT KNOW WHY THE ACFT FAILED TO MAINTAIN CABIN ALT.

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.