A fokker 100 in cruise at FL330 declared an emergency and made an emergency descent due to loss of c...

Attributes
ACN	389718
Time
Date	199712
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : jan
State Reference	MS
Altitude	msl bound lower : 33000 msl bound upper : 33000
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zme
Operator	common carrier : air carrier
Make Model Name	Fokker 100
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other descent other other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	389718
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	aircraft equipment problem : critical inflight encounter : weather other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : exited adverse environment flight crew : declared emergency other
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

Cruising at FL330 in IMC icing conditions and moderate turbulence with anti-ice on. While talking on interphone with flight attendant about advisability of sitting down and buckling up, we received an unexpected cabin altitude warning with triple chime. A quick glance revealed cabin altitude above 10000 ft and climbing at about 800 FPM. Anxious to avoid passenger mask presentation, elected emergency descent to 10000 ft. Declared emergency and received appropriate clearance. Now faced with 2 conflicting needs. Rapid descent requires idle power and icing conditions and still rapidly climbing cabin requires increased power. Experimented briefly with power increase which caused autospd brake retraction and rapid acceleration through clacker speed. Recovered smoothly. Sometimes things seem to snowball. Level at 10000 ft, anti-ice worked normally and cabin stabilized in comfortable descent. Discussed circumstances, position and fuel on board with dispatch and mutually decided to continue to atl. FMC predicted arrival with comfortable reserves at cruise altitude of 10000 ft. Remainder of trip uneventful except for IMC with icing conditions and frequent moderate chop. Advised maintenance of all particulars including overspd for appropriate inspection -- which revealed no damage. Callback conversation with reporter revealed the following information: the reporter stated the aircraft cabin started to climb at FL330 and then stabilized when reaching 10000 ft. The reporter said a log item was made on the pressurization system and overspd check that was required. The reporter states that maintenance could find nothing wrong with the pressurization system and cleared the item. The reporter states that 1 week after this incident the reporter again operates the same airplane at FL330 with no icing conditions and the cabin pressure is normal until the airfoil anti-ice is switched on and the pneumatic duct pressure drops abnormally. The reporter said that maintenance did not report the fix for this problem.

Original NASA ASRS Text

Title: A FOKKER 100 IN CRUISE AT FL330 DECLARED AN EMER AND MADE AN EMER DSCNT DUE TO LOSS OF CABIN PRESSURIZATION.

Narrative: CRUISING AT FL330 IN IMC ICING CONDITIONS AND MODERATE TURB WITH ANTI-ICE ON. WHILE TALKING ON INTERPHONE WITH FLT ATTENDANT ABOUT ADVISABILITY OF SITTING DOWN AND BUCKLING UP, WE RECEIVED AN UNEXPECTED CABIN ALT WARNING WITH TRIPLE CHIME. A QUICK GLANCE REVEALED CABIN ALT ABOVE 10000 FT AND CLBING AT ABOUT 800 FPM. ANXIOUS TO AVOID PAX MASK PRESENTATION, ELECTED EMER DSCNT TO 10000 FT. DECLARED EMER AND RECEIVED APPROPRIATE CLRNC. NOW FACED WITH 2 CONFLICTING NEEDS. RAPID DSCNT REQUIRES IDLE PWR AND ICING CONDITIONS AND STILL RAPIDLY CLBING CABIN REQUIRES INCREASED PWR. EXPERIMENTED BRIEFLY WITH PWR INCREASE WHICH CAUSED AUTOSPD BRAKE RETRACTION AND RAPID ACCELERATION THROUGH CLACKER SPD. RECOVERED SMOOTHLY. SOMETIMES THINGS SEEM TO SNOWBALL. LEVEL AT 10000 FT, ANTI-ICE WORKED NORMALLY AND CABIN STABILIZED IN COMFORTABLE DSCNT. DISCUSSED CIRCUMSTANCES, POS AND FUEL ON BOARD WITH DISPATCH AND MUTUALLY DECIDED TO CONTINUE TO ATL. FMC PREDICTED ARR WITH COMFORTABLE RESERVES AT CRUISE ALT OF 10000 FT. REMAINDER OF TRIP UNEVENTFUL EXCEPT FOR IMC WITH ICING CONDITIONS AND FREQUENT MODERATE CHOP. ADVISED MAINT OF ALL PARTICULARS INCLUDING OVERSPD FOR APPROPRIATE INSPECTION -- WHICH REVEALED NO DAMAGE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE ACFT CABIN STARTED TO CLB AT FL330 AND THEN STABILIZED WHEN REACHING 10000 FT. THE RPTR SAID A LOG ITEM WAS MADE ON THE PRESSURIZATION SYS AND OVERSPD CHK THAT WAS REQUIRED. THE RPTR STATES THAT MAINT COULD FIND NOTHING WRONG WITH THE PRESSURIZATION SYS AND CLRED THE ITEM. THE RPTR STATES THAT 1 WK AFTER THIS INCIDENT THE RPTR AGAIN OPERATES THE SAME AIRPLANE AT FL330 WITH NO ICING CONDITIONS AND THE CABIN PRESSURE IS NORMAL UNTIL THE AIRFOIL ANTI-ICE IS SWITCHED ON AND THE PNEUMATIC DUCT PRESSURE DROPS ABNORMALLY. THE RPTR SAID THAT MAINT DID NOT RPT THE FIX FOR THIS PROB.

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.

A fokker 100 in cruise at FL330 declared an emergency and made an emergency descent due to loss of cabin pressurization.