A return land by air carrier medium large transport mandated by loss of cabin pressure control.

Attributes
ACN	202415
Time
Date	199202
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : slt
State Reference	PA
Altitude	msl bound lower : 33000 msl bound upper : 33000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zny
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other descent other other
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 10000 flight time type : 5000
ASRS Report	202415
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	other flight crewa
Resolutory Action	flight crew : exited adverse environment flight crew : declared emergency other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

The cabin altitude continued to climb as we leveled at FL330 and reduced power to cruise. The automatic controller had switched to standby system and transfer lockout prevented us from trying the other controller. We selected manual control of the outflow valve and fully closed it but the cabin continued to climb at 800-1000 FPM. We requested lower altitude and a turn back to our origin (pit). Center cleared us to descend and turn and we began this while the cabin began to pass through 10,000 ft. We donned oxygen masks and I asked for the checklists after we had established communications. I did not feel an emergency existed, but the emergency checklist was probably the most appropriate tool for the situation. Also, during idle descent with the outflow valve fully closed (manual) the cabin altitude abruptly reversed and began rapid descent, which required manual opening of the outflow valve. We continued to 10,000 ft and leveled off, took off our masks and because the leak in the cabin apparently fixed itself, we elected to try the automatic system again and it worked fine during our flight back to pit. The cabin altitude may have exceeded 13,000 ft but definitely not 14,000 ft as the passenger oxygen masks did not deploy. Routine landing conducted in pit.

Original NASA ASRS Text

Title: A RETURN LAND BY ACR MLG MANDATED BY LOSS OF CABIN PRESSURE CTL.

Narrative: THE CABIN ALT CONTINUED TO CLB AS WE LEVELED AT FL330 AND REDUCED PWR TO CRUISE. THE AUTOMATIC CTLR HAD SWITCHED TO STANDBY SYS AND TRANSFER LOCKOUT PREVENTED US FROM TRYING THE OTHER CTLR. WE SELECTED MANUAL CTL OF THE OUTFLOW VALVE AND FULLY CLOSED IT BUT THE CABIN CONTINUED TO CLB AT 800-1000 FPM. WE REQUESTED LOWER ALT AND A TURN BACK TO OUR ORIGIN (PIT). CTR CLRED US TO DSND AND TURN AND WE BEGAN THIS WHILE THE CABIN BEGAN TO PASS THROUGH 10,000 FT. WE DONNED OXYGEN MASKS AND I ASKED FOR THE CHKLISTS AFTER WE HAD ESTABLISHED COMS. I DID NOT FEEL AN EMER EXISTED, BUT THE EMER CHKLIST WAS PROBABLY THE MOST APPROPRIATE TOOL FOR THE SITUATION. ALSO, DURING IDLE DSCNT WITH THE OUTFLOW VALVE FULLY CLOSED (MANUAL) THE CABIN ALT ABRUPTLY REVERSED AND BEGAN RAPID DSCNT, WHICH REQUIRED MANUAL OPENING OF THE OUTFLOW VALVE. WE CONTINUED TO 10,000 FT AND LEVELED OFF, TOOK OFF OUR MASKS AND BECAUSE THE LEAK IN THE CABIN APPARENTLY FIXED ITSELF, WE ELECTED TO TRY THE AUTOMATIC SYS AGAIN AND IT WORKED FINE DURING OUR FLT BACK TO PIT. THE CABIN ALT MAY HAVE EXCEEDED 13,000 FT BUT DEFINITELY NOT 14,000 FT AS THE PAX OXYGEN MASKS DID NOT DEPLOY. ROUTINE LNDG CONDUCTED IN PIT.

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.