A ce-501 squat switch failed at FL350 causing a rapid loss of pressurization; so an emergency was de...

Attributes
ACN	1039317
Time
Date	201209
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Make Model Name	Citation I/SP (C501)
Operating Under FAR Part	Part 91
Flight Phase	Cruise
Route In Use	Vectors
Flight Plan	IFR
Component
Aircraft Component	Squat Switch
Person 1
Function	First Officer Pilot Flying
Qualification	Flight Crew Multiengine Flight Crew Flight Instructor Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 50 Flight Crew Total 8600 Flight Crew Type 25
Person 2
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 25 Flight Crew Total 13800 Flight Crew Type 600
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Procedural Published Material / Policy Inflight Event / Encounter Weather / Turbulence

Narrative:

We had just experienced severe turbulence less than 5 minutes before when the 10;000 ft cabin horn sounded. We quickly donned our oxygen masks and the PIC declared an emergency with the ARTCC and indicated we were going to perform an emergency descent. I disconnected the autopilot and pitched over to the appropriate attitude to execute the emergency descent and confirmed that the throttles and speed brakes were in the proper position. It appeared that the ARTCC may or may not have understood what the PIC had told them so I also informed them that we were making an emergency descent. The ARTCC told us to maintain several altitudes; (FL240 and FL210); and I again informed them of the nature of our descent and they finally cleared us to 15;000. We requested 11;000 as a final altitude and terminated the emergency and requested to proceed to our destination airport. One thing we had forgotten to do was change our transponder to 7700. After accessing the situation we believe our pressurization system had failed; but at 11;000 ft it began to operate properly. The PIC had maintenance troubleshoot the system but they could not find anything definitively wrong with it. We continued on our trip at altitudes not requiring pressurization and it worked properly thereafter. As a precaution when we deadheaded home we remained at altitudes were we could use our masks and not have to descend. The pressurization system has performed perfectly since the incident described above.

Original NASA ASRS Text

Title: A CE-501 squat switch failed at FL350 causing a rapid loss of pressurization; so an emergency was declared and the flight descended to 11;000 FT then continued to its planned destination.

Narrative: We had just experienced severe turbulence less than 5 minutes before when the 10;000 FT cabin horn sounded. We quickly donned our oxygen masks and the PIC declared an emergency with the ARTCC and indicated we were going to perform an emergency descent. I disconnected the autopilot and pitched over to the appropriate attitude to execute the emergency descent and confirmed that the throttles and speed brakes were in the proper position. It appeared that the ARTCC may or may not have understood what the PIC had told them so I also informed them that we were making an emergency descent. The ARTCC told us to maintain several altitudes; (FL240 and FL210); and I again informed them of the nature of our descent and they finally cleared us to 15;000. We requested 11;000 as a final altitude and terminated the emergency and requested to proceed to our destination airport. One thing we had forgotten to do was change our transponder to 7700. After accessing the situation we believe our pressurization system had failed; but at 11;000 FT it began to operate properly. The PIC had maintenance troubleshoot the system but they could not find anything definitively wrong with it. We continued on our trip at altitudes not requiring pressurization and it worked properly thereafter. As a precaution when we deadheaded home we remained at altitudes were we could use our masks and not have to descend. The pressurization system has performed perfectly since the incident described above.

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.

A ce-501 squat switch failed at FL350 causing a rapid loss of pressurization; so an emergency was declared and the flight descended to 11;000 ft then continued to its planned destination.