A G200 in cruise at FL390 made an emergency descent due to cabin pressure increasing slowly from gre...

Attributes
ACN	636126
Time
Date	200411
Day	Fri
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl bound lower : 31000 msl bound upper : 39000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zzz.artcc
Operator	common carrier : air taxi
Make Model Name	Gulfstream 200 [G200] (IAI 1126 Galaxy)
Operating Under FAR Part	Part 135
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air taxi
Function	flight crew : first officer
Qualification	pilot : commercial pilot : atp pilot : multi engine
Experience	flight time last 90 days : 100 flight time total : 14800 flight time type : 1000
ASRS Report	636126
Person 2
Affiliation	company : air taxi
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 120 flight time total : 3700 flight time type : 120
ASRS Report	636182
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude
Independent Detector	aircraft equipment other aircraft equipment : eicas-pressure indication other flight crewa other flight crewb
Resolutory Action	controller : separated traffic flight crew : declared emergency flight crew : took evasive action
Consequence	other other
Supplementary
Problem Areas	Flight Crew Human Performance Environmental Factor Chart Or Publication Aircraft
Primary Problem	Aircraft

Narrative:

Aircraft, part 135 charter with two passenger, in IMC conditions, had been at FL390 for approximately 30 mins. Time was xa:45 on fri-04. Radar and radio contact with ZZZ center. At the above stated time, I noticed that there was a problem with our pressurization system and we could not control it. The pressure differential was into the red zone, so we went to the checklist. While going through the checklist, the problem was getting worse. I, PNF, asked for an immediate descent to a lower altitude. No response from ATC. I asked again and looked up and saw our altitude was at FL387 and decreasing. While all of this was going on, I was able to manually take control of the pressurization system. ATC informed us, after the PF executed an emergency maneuver (with traffic in sight), to dscnd to a safer altitude. We controled the pressurization system, leveled off at FL310 and continued to our destination. We called ZZZ at xb:30. This problem was subtle, only indication on EICAS was a small pressurization differential number going from green 8.8 psi to amber 8.9 psi to red at 9.0-9.2 psi. Had to search through checklist to find correct page, even though there was a red indication (on pressurization differential) there was no alerting signals and no master warning/master caution. The maintenance facility stated at 10 psi differential, there would be structural failure. Callback conversation with reporter revealed the following information: the reporter stated that maintenance replaced the automatic pressure controller and tested ok. When the reporter was asked if the over pressure relief was replaced or tested, the reporter answered, 'no, but might be a good idea.'

Original NASA ASRS Text

Title: A G200 IN CRUISE AT FL390 MADE AN EMER DSCNT DUE TO CABIN PRESSURE INCREASING SLOWLY FROM GREEN INDICATION 8.8 PSI, TO AMBER 8.9, AND THEN TO RED AT 9.0-9.2 PSI. THEY WERE FINALLY ABLE TO CTL CABIN PRESSURE MANUALLY AT FL310.

Narrative: ACFT, PART 135 CHARTER WITH TWO PAX, IN IMC CONDITIONS, HAD BEEN AT FL390 FOR APPROX 30 MINS. TIME WAS XA:45 ON FRI-04. RADAR AND RADIO CONTACT WITH ZZZ CTR. AT THE ABOVE STATED TIME, I NOTICED THAT THERE WAS A PROB WITH OUR PRESSURIZATION SYSTEM AND WE COULD NOT CTL IT. THE PRESSURE DIFFERENTIAL WAS INTO THE RED ZONE, SO WE WENT TO THE CHKLIST. WHILE GOING THROUGH THE CHKLIST, THE PROB WAS GETTING WORSE. I, PNF, ASKED FOR AN IMMEDIATE DSCNT TO A LOWER ALT. NO RESPONSE FROM ATC. I ASKED AGAIN AND LOOKED UP AND SAW OUR ALT WAS AT FL387 AND DECREASING. WHILE ALL OF THIS WAS GOING ON, I WAS ABLE TO MANUALLY TAKE CTL OF THE PRESSURIZATION SYSTEM. ATC INFORMED US, AFTER THE PF EXECUTED AN EMER MANEUVER (WITH TFC IN SIGHT), TO DSCND TO A SAFER ALT. WE CTLED THE PRESSURIZATION SYSTEM, LEVELED OFF AT FL310 AND CONTINUED TO OUR DEST. WE CALLED ZZZ AT XB:30. THIS PROB WAS SUBTLE, ONLY INDICATION ON EICAS WAS A SMALL PRESSURIZATION DIFFERENTIAL NUMBER GOING FROM GREEN 8.8 PSI TO AMBER 8.9 PSI TO RED AT 9.0-9.2 PSI. HAD TO SEARCH THROUGH CHKLIST TO FIND CORRECT PAGE, EVEN THOUGH THERE WAS A RED INDICATION (ON PRESSURIZATION DIFFERENTIAL) THERE WAS NO ALERTING SIGNALS AND NO MASTER WARNING/MASTER CAUTION. THE MAINT FACILITY STATED AT 10 PSI DIFFERENTIAL, THERE WOULD BE STRUCTURAL FAILURE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT MAINT REPLACED THE AUTOMATIC PRESSURE CTLR AND TESTED OK. WHEN THE RPTR WAS ASKED IF THE OVER PRESSURE RELIEF WAS REPLACED OR TESTED, THE RPTR ANSWERED, 'NO, BUT MIGHT BE A GOOD IDEA.'

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 G200 in cruise at FL390 made an emergency descent due to cabin pressure increasing slowly from green indication 8.8 psi, to amber 8.9, and then to red at 9.0-9.2 psi. They were finally able to control cabin pressure manually at FL310.