The flight crew of a B757-200 began an emergency descent when they received a cabin altitude warning...

Narrative:

During cruise flight at FL380; we received a 'cabin altitude' EICAS alert accompanied by a warning horn. We confirmed the cabin altitude was slightly above 10;000 MSL and showing an extremely slow rate of climb (less than 200 FPM). In addition the cabin differential pressure was extremely low for the altitude we were at. We then donned our O2 masks. The captain declared an emergency with ATC and I began an emergency descent out of FL380. During the descent the captain managed to control the cabin rate of climb by switching from 'auto controller #2' to 'manual' and later by switching to 'auto controller #1'. Once the pressurization system had been switched over to another auto controller and was reacting normally; we decided to halt our descent at FL300. The cabin continued to descend to the normal cabin altitude and differential pressure began to increase to a normal level for FL300. We decided that continued flight was possible and informed ATC that we would cancel the emergency and continue to our destination. The rest of the flight proceeded normally and we landed without incident.

Original NASA ASRS Text

Title: The flight crew of a B757-200 began an emergency descent when they received a cabin altitude warning at FL380. When the Captain stabilized the system by selecting an alternate pressure controller they canceled the emergency and continued to their destination at FL300.

Narrative: During cruise flight at FL380; we received a 'Cabin Altitude' EICAS alert accompanied by a warning horn. We confirmed the cabin altitude was slightly above 10;000 MSL and showing an extremely slow rate of climb (less than 200 FPM). In addition the cabin differential pressure was extremely low for the altitude we were at. We then donned our O2 masks. The Captain declared an emergency with ATC and I began an emergency descent out of FL380. During the descent the Captain managed to control the Cabin rate of climb by switching from 'Auto Controller #2' to 'Manual' and later by switching to 'Auto Controller #1'. Once the Pressurization system had been switched over to another Auto Controller and was reacting normally; we decided to halt our descent at FL300. The Cabin continued to descend to the normal Cabin Altitude and differential pressure began to increase to a normal level for FL300. We decided that continued flight was possible and informed ATC that we would cancel the emergency and continue to our destination. The rest of the flight proceeded normally and we landed without incident.

Data retrieved from NASA's ASRS site as of July 2013 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.

Attributes
ACN	1040366
Time
Date	201209
Aircraft 1
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Component
Aircraft Component	Pressurization System
Person 1
Function	First Officer Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Person 2
Function	Pilot Not Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Total 22000
Events
Anomaly	Aircraft Equipment Problem Critical

The flight crew of a B757-200 began an emergency descent when they received a cabin altitude warning at FL380. When the captain stabilized the system by selecting an alternate pressure controller they canceled the emergency and continued to their destination at FL300.