Altitude excursion when a lear-35 flight crew has to leave their assigned altitudes during a rapid descent after losing control of their cabin pressure at FL380 near psb, PA.

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Attributes
ACN	590654
Time
Date	200308
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : psb.vortac
State Reference	PA
Altitude	msl bound lower : 25000 msl bound upper : 38000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zny.artcc
Operator	general aviation : corporate
Make Model Name	Learjet 35
Operating Under FAR Part	Part 91
Flight Phase	climbout : intermediate altitude climbout : vacating altitude
Flight Plan	IFR
Person 1
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 100 flight time total : 3500 flight time type : 1500
ASRS Report	590654
Person 2
Affiliation	company : corporate
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude altitude deviation : overshoot non adherence : published procedure non adherence : clearance
Independent Detector	other flight crewa other flight crewb
Resolutory Action	controller : issued new clearance flight crew : overcame equipment problem other
Consequence	faa : reviewed incident with flight crew Other
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

Aircraft was in a climb to FL390, passing through FL330. A change in cabin pressure was felt. Both pilots noted that the cabin had started a rapid climb of 2500 FPM. The PNF immediately tried to correct the situation by placing the pressurization into the manual mode. This did not affect the cabin. The PNF then asked for a lower altitude. ATC cleared us to FL350. We immediately started a rapid descent. We tried to ask for a lower altitude as we approached FL350. The frequency was very busy and we could not contact ATC. We continued to approximately FL340 before we could receive clearance to FL310. We then asked for a descent to FL250. ATC cleared us to FL250. We leveled off at FL250 where the cabin was able to maintain a safe altitude. An emergency was never declared. ATC did not query situation except to ask if we needed lower than FL250 or if we needed any other assistance. We squawked identify as we descended through FL350. This aircraft was test flown the day before for similar problem. I did the test flight myself. Pressurization was perfect.

Original NASA ASRS Text

Title: ALT EXCURSION WHEN A LEAR-35 FLT CREW HAS TO LEAVE THEIR ASSIGNED ALTS DURING A RAPID DSCNT AFTER LOSING CTL OF THEIR CABIN PRESSURE AT FL380 NEAR PSB, PA.

Narrative: ACFT WAS IN A CLB TO FL390, PASSING THROUGH FL330. A CHANGE IN CABIN PRESSURE WAS FELT. BOTH PLTS NOTED THAT THE CABIN HAD STARTED A RAPID CLB OF 2500 FPM. THE PNF IMMEDIATELY TRIED TO CORRECT THE SIT BY PLACING THE PRESSURIZATION INTO THE MANUAL MODE. THIS DID NOT AFFECT THE CABIN. THE PNF THEN ASKED FOR A LOWER ALT. ATC CLRED US TO FL350. WE IMMEDIATELY STARTED A RAPID DSCNT. WE TRIED TO ASK FOR A LOWER ALT AS WE APCHED FL350. THE FREQ WAS VERY BUSY AND WE COULD NOT CONTACT ATC. WE CONTINUED TO APPROX FL340 BEFORE WE COULD RECEIVE CLRNC TO FL310. WE THEN ASKED FOR A DSCNT TO FL250. ATC CLRED US TO FL250. WE LEVELED OFF AT FL250 WHERE THE CABIN WAS ABLE TO MAINTAIN A SAFE ALT. AN EMER WAS NEVER DECLARED. ATC DID NOT QUERY SIT EXCEPT TO ASK IF WE NEEDED LOWER THAN FL250 OR IF WE NEEDED ANY OTHER ASSISTANCE. WE SQUAWKED IDENT AS WE DSNDED THROUGH FL350. THIS ACFT WAS TEST FLOWN THE DAY BEFORE FOR SIMILAR PROB. I DID THE TEST FLT MYSELF. PRESSURIZATION WAS PERFECT.

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.