A P180 auto pressurization failed at 14;000 ft in the climb. An emergency was declared; a descent be...

Narrative:

I was the PIC and pilot flying. We departed with pressurization in auto mode. Pressurization was functioning normally until 14;000 ft where auto mode failed initially. The cabin altitude began an immediate 6;000 FPM rate of climb. We informed ATC we needed to descend and return to our departure airport as we attempted to drive the cabin back down in manual mode unsuccessfully. In manual mode the cabin remained in a 4;000-6;000 FPM rate of climb the cabin pressure light illuminated and the cabin continued to climb further. At that time; we declared an emergency and squawked 7700. The ATC controller assigned us 10;000. With the cabin press light still illuminated and cabin still rising rapidly we exercised our emergency authority and continued our descent to 9;500 (at this point cabin altitude (10;500) was greater than indicated altitude (9;500) a very abnormal situation!). I deviated from the controllers instructions (maintain 10;000) initially strictly to meet the need of our emergency situation. The controller informed us of a aircraft below us and asked us to arrest our descent until he could vector him away. After I was informed of the conflicting aircraft and saw him on our TCAS; we climbed back to 10;000 until the aircraft was clear. We then descended aggressively with the controllers guidance. We performed the appropriate checklist (cabin press light) as soon as our situation would allow. Reaching 4;000 ft the pressure began to equalize in manual mode. 10 miles outside of our destination we canceled our emergency when the light extinguished; pressure stabilized; and we landed safely.

Original NASA ASRS Text

Title: A P180 auto pressurization failed at 14;000 FT in the climb. An emergency was declared; a descent begun; and as the flight returned to the departure airport the pressurization system stabilized at 4;000 FT in the manual mode.

Narrative: I was the PIC and pilot flying. We departed with pressurization in auto mode. Pressurization was functioning normally until 14;000 FT where auto mode failed initially. The cabin altitude began an immediate 6;000 FPM rate of climb. We informed ATC we needed to descend and return to our departure airport as we attempted to drive the cabin back down in manual mode unsuccessfully. In manual mode the cabin remained in a 4;000-6;000 FPM rate of climb the cabin pressure light illuminated and the cabin continued to climb further. At that time; we declared an emergency and squawked 7700. The ATC Controller assigned us 10;000. With the cabin press light still illuminated and cabin still rising rapidly we exercised our emergency authority and continued our descent to 9;500 (at this point cabin altitude (10;500) was greater than indicated altitude (9;500) a very abnormal situation!). I deviated from the Controllers instructions (maintain 10;000) initially strictly to meet the need of our emergency situation. The Controller informed us of a aircraft below us and asked us to arrest our descent until he could vector him away. After I was informed of the conflicting aircraft and saw him on our TCAS; we climbed back to 10;000 until the aircraft was clear. We then descended aggressively with the Controllers guidance. We performed the appropriate checklist (cabin press light) as soon as our situation would allow. Reaching 4;000 FT the pressure began to equalize in manual mode. 10 miles outside of our destination we canceled our emergency when the light extinguished; pressure stabilized; and we landed safely.

Data retrieved from NASA's ASRS site as of April 2012 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	951152
Time
Date	201105
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	P180 Avanti
Operating Under FAR Part	Part 135
Flight Phase	Climb
Route In Use	Direct
Flight Plan	IFR
Component
Aircraft Component	Pressurization Control System
Person 1
Function	Pilot Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 150 Flight Crew Total 4000 Flight Crew Type 2500
Person 2
Function	First Officer Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Flight Instructor Flight Crew Multiengine Flight Crew Instrument
Experience	Flight Crew Last 90 Days 200 Flight Crew Total 3800 Flight Crew Type 250
Events
Anomaly	Aircraft Equipment Problem Critical

A P180 auto pressurization failed at 14;000 ft in the climb. An emergency was declared; a descent begun; and as the flight returned to the departure airport the pressurization system stabilized at 4;000 ft in the manual mode.