An HS125 at FL390 experienced an automatic press malfunction. An emergency was declared with a desce...

Attributes
ACN	766527
Time
Date	200712
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl single value : 39000
Environment
Flight Conditions	VMC IMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zzz.artcc
Operator	general aviation : personal
Make Model Name	HS 125 Series
Operating Under FAR Part	Part 91
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	other
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 180 flight time type : 150
ASRS Report	766527
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 180 flight time total : 13500 flight time type : 150
ASRS Report	766540
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	aircraft equipment other aircraft equipment : cabin alt light other flight crewa other flight crewb
Resolutory Action	flight crew : exited adverse environment flight crew : declared emergency flight crew : diverted to another airport other
Consequence	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

We were climbing to FL390 en route to ZZZ2. As soon as we leveled off we noted an abnormal situation with our cabin altitude indication and we started working with the emergency pressurization system; we received a cabin altitude light in our mws (master warning system) and we took action with our QRH making the emergency procedure but we couldn't control it and we started an emergency descent to 10000 ft; we were always in communication with center and also declared our emergency by using southwest 7700 during the descent. After that we flew to ZZZ1 airport because we have our maintenance base there and; we reported the problem. Maintenance was working on the aircraft almost 2 days and they changed a filter from the water separation system; and they didn't find anything else. After that we flew the aircraft as a test flight to ZZZ2; and during the flight we made some procedure checks at 15000 ft and we noted that the pressurization worked good; however hawker beechcraft suggested that if we still have a pressurization control system with part number ending with (-4) we must change for a new one with a part number ending with (-5).

Original NASA ASRS Text

Title: AN HS125 AT FL390 EXPERIENCED AN AUTO PRESS MALFUNCTION. AN EMER WAS DECLARED WITH A DESCENT TO 10000 FT AND A DIVERSION TO A NEARBY ARPT.

Narrative: WE WERE CLBING TO FL390 ENRTE TO ZZZ2. AS SOON AS WE LEVELED OFF WE NOTED AN ABNORMAL SITUATION WITH OUR CABIN ALT INDICATION AND WE STARTED WORKING WITH THE EMER PRESSURIZATION SYS; WE RECEIVED A CABIN ALT LIGHT IN OUR MWS (MASTER WARNING SYS) AND WE TOOK ACTION WITH OUR QRH MAKING THE EMER PROC BUT WE COULDN'T CTL IT AND WE STARTED AN EMER DSCNT TO 10000 FT; WE WERE ALWAYS IN COM WITH CTR AND ALSO DECLARED OUR EMER BY USING SW 7700 DURING THE DSCNT. AFTER THAT WE FLEW TO ZZZ1 ARPT BECAUSE WE HAVE OUR MAINT BASE THERE AND; WE RPTED THE PROB. MAINT WAS WORKING ON THE ACFT ALMOST 2 DAYS AND THEY CHANGED A FILTER FROM THE WATER SEPARATION SYS; AND THEY DIDN'T FIND ANYTHING ELSE. AFTER THAT WE FLEW THE ACFT AS A TEST FLT TO ZZZ2; AND DURING THE FLT WE MADE SOME PROC CHKS AT 15000 FT AND WE NOTED THAT THE PRESSURIZATION WORKED GOOD; HOWEVER HAWKER BEECHCRAFT SUGGESTED THAT IF WE STILL HAVE A PRESSURIZATION CTL SYS WITH PART NUMBER ENDING WITH (-4) WE MUST CHANGE FOR A NEW ONE WITH A PART NUMBER ENDING WITH (-5).

Data retrieved from NASA's ASRS site as of January 2009 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.

An HS125 at FL390 experienced an automatic press malfunction. An emergency was declared with a descent to 10000 ft and a diversion to a nearby airport.