Cessna 550 flight crew has pressurization problems and executes an emergency descent and elects to d...

Attributes
ACN	576171
Time
Date	200303
Day	Sun
Local Time Of Day	0601 To 1200
Place
Locale Reference	navaid : tay.vortac
State Reference	FL
Altitude	msl single value : 39000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zjx.artcc
Operator	other
Make Model Name	Citation II S2/Bravo
Operating Under FAR Part	Part 91
Navigation In Use	other vortac
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	government other
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : cfi pilot : commercial pilot : atp
Experience	flight time last 90 days : 60 flight time total : 5000 flight time type : 700
ASRS Report	576171
Person 2
Affiliation	government other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : critical cabin event other other anomaly other
Independent Detector	other flight crewa other flight crewb
Resolutory Action	controller : provided flight assist flight crew : diverted to another airport flight crew : landed as precaution flight crew : declared emergency other
Consequence	other
Supplementary
Problem Areas	Environmental Factor Aircraft
Primary Problem	Aircraft

Narrative:

On mar/sun/03, we departed rsw at approximately XA15 with 1 passenger on a flight to blacksburg, va. First officer was flying, and I was serving as copilot. Soon after we leveled at FL390, we heard a loud noise similar to a fire horn. We both suspected a door seal problem, and we began an emergency descent following procedures as taught yearly in training. ATC cleared us to descend to 10000 ft. When asked by ATC to declare our intentions, I requested the nearest VFR airport. ATC then cleared us to tampa. The remainder of the flight was uneventful. After arriving at tampa, I contacted the service center in orlando and discussed our problem with a maintenance supervisor. He thought the problem could be in the door seal or the air cycle machine. After the WX cleared in orlando, we flew over at 9000 ft non-pressurized as per our MEL. After some time spent trouble-shooting, the maintenance technician found water in the bleed air line that inflates the door seal. The moisture accumulates over time and is caused by temperature changes as the air travels from the engine through the air line. It was determined that the water froze at altitude, blocking the air to the seal, causing it to deflate. The outside temperature at FL390 was minus 40 degrees C. I also had the technician replace the door seal, because when inflated on the ground for inspection, it had 2 weak spots that could cause problems in the future. The technician explained that newer aircraft have a canister that collects the moisture, thus preventing the freezing of the air line. He also said that adding extra insulation around the air line has been done to modify some older aircraft like ours. He explained how we should go about checking the air line for moisture periodically. I passed the information on to maintenance and the other pilots. Our return flight from orlando to richmond on mar/mon/03 was also uneventful. The pressurization system worked as it should.

Original NASA ASRS Text

Title: CESSNA 550 FLT CREW HAS PRESSURIZATION PROBS AND EXECUTES AN EMER DSCNT AND ELECTS TO DIVERT TO TPA.

Narrative: ON MAR/SUN/03, WE DEPARTED RSW AT APPROX XA15 WITH 1 PAX ON A FLT TO BLACKSBURG, VA. FO WAS FLYING, AND I WAS SERVING AS COPLT. SOON AFTER WE LEVELED AT FL390, WE HEARD A LOUD NOISE SIMILAR TO A FIRE HORN. WE BOTH SUSPECTED A DOOR SEAL PROB, AND WE BEGAN AN EMER DSCNT FOLLOWING PROCS AS TAUGHT YEARLY IN TRAINING. ATC CLRED US TO DSND TO 10000 FT. WHEN ASKED BY ATC TO DECLARE OUR INTENTIONS, I REQUESTED THE NEAREST VFR ARPT. ATC THEN CLRED US TO TAMPA. THE REMAINDER OF THE FLT WAS UNEVENTFUL. AFTER ARRIVING AT TAMPA, I CONTACTED THE SVC CTR IN ORLANDO AND DISCUSSED OUR PROB WITH A MAINT SUPVR. HE THOUGHT THE PROB COULD BE IN THE DOOR SEAL OR THE AIR CYCLE MACHINE. AFTER THE WX CLRED IN ORLANDO, WE FLEW OVER AT 9000 FT NON-PRESSURIZED AS PER OUR MEL. AFTER SOME TIME SPENT TROUBLE-SHOOTING, THE MAINT TECHNICIAN FOUND WATER IN THE BLEED AIR LINE THAT INFLATES THE DOOR SEAL. THE MOISTURE ACCUMULATES OVER TIME AND IS CAUSED BY TEMP CHANGES AS THE AIR TRAVELS FROM THE ENG THROUGH THE AIR LINE. IT WAS DETERMINED THAT THE WATER FROZE AT ALT, BLOCKING THE AIR TO THE SEAL, CAUSING IT TO DEFLATE. THE OUTSIDE TEMP AT FL390 WAS MINUS 40 DEGS C. I ALSO HAD THE TECHNICIAN REPLACE THE DOOR SEAL, BECAUSE WHEN INFLATED ON THE GND FOR INSPECTION, IT HAD 2 WEAK SPOTS THAT COULD CAUSE PROBS IN THE FUTURE. THE TECHNICIAN EXPLAINED THAT NEWER ACFT HAVE A CANISTER THAT COLLECTS THE MOISTURE, THUS PREVENTING THE FREEZING OF THE AIR LINE. HE ALSO SAID THAT ADDING EXTRA INSULATION AROUND THE AIR LINE HAS BEEN DONE TO MODIFY SOME OLDER ACFT LIKE OURS. HE EXPLAINED HOW WE SHOULD GO ABOUT CHKING THE AIR LINE FOR MOISTURE PERIODICALLY. I PASSED THE INFO ON TO MAINT AND THE OTHER PLTS. OUR RETURN FLT FROM ORLANDO TO RICHMOND ON MAR/MON/03 WAS ALSO UNEVENTFUL. THE PRESSURIZATION SYS WORKED AS IT SHOULD.

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.

Cessna 550 flight crew has pressurization problems and executes an emergency descent and elects to divert to tpa.