Hs-25B crew lost control of the cabin pressurization control in ZOB class a airspace.

Attributes
ACN	550075
Time
Date	200206
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : btl.airport
State Reference	MI
Altitude	msl bound lower : 24000 msl bound upper : 28000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zob.artcc tracon : azo.tracon
Operator	general aviation : corporate
Make Model Name	HS 125 Series 700
Operating Under FAR Part	Part 91
Navigation In Use	other
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 50 flight time total : 7400 flight time type : 230
ASRS Report	550075
Person 2
Affiliation	company : corporate
Function	flight crew : first officer
Qualification	pilot : atp pilot : cfi
Experience	flight time last 90 days : 50 flight time total : 5000 flight time type : 500
ASRS Report	550076
Events
Anomaly	aircraft equipment problem : critical altitude deviation : overshoot other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : acft cabin diffential indicator altimeter other flight crewa other flight crewb
Resolutory Action	controller : issued new clearance controller : provided flight assist flight crew : declared emergency flight crew : diverted to another airport none taken : detected after the fact other
Consequence	other
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

After takeoff from yip and assigned a best rate climb, the aircraft was displaying some erratic pressurization rate indications. We were working at maintaining proper pressurization rate through the climb and realized that the airplane was not going to pressurize normally. Using manual pressurization control, backed up with our checklist for automatic pressure control failure, we were able to maintain some rate control. We were assigned a higher altitude and a crew decision was made to discontinue the climb, terminate the flight and return home. We stopped the climb between FL290 and FL300. A request was made for a lower altitude and to return to our point of departure, which was granted by ATC. We were assigned FL280 and heading 270 degrees a right turn of about 30 degrees. A descent was started in an effort to regain any control over the pressurization and bring the cabin to a safe altitude, anticipating no delays in descent. ATC inquired about our descent request and flight plan change and we advised them of our pressurization problem and requested even lower. In the continued effort to regain pressurization control, we descended below our assigned altitude of FL280. We were assigned FL240, but the pressurization problem would not allow us to hold FL240 and the descent was continued, along with an additional request for a lower altitude. ATC granted our request for lower and we were assigned 15000 ft and a new ATC frequency. Upon the radio change, we were assigned 11000 ft and leveled at that altitude with the new controller. It was at this altitude the pressurization rate was no longer a problem. We were switched to battle creek approach, which granted us a hold at 7000 ft to assess our situation and reduce our fuel load. We held for approximately 45 mins then returned to our point of departure and landed without incident. After review of the situation by the crew, a stop of the climb sooner would have lessened the urgency for descent and reduced the effects of any pressurization problem.

Original NASA ASRS Text

Title: HS-25B CREW LOST CTL OF THE CABIN PRESSURIZATION CTL IN ZOB CLASS A AIRSPACE.

Narrative: AFTER TKOF FROM YIP AND ASSIGNED A BEST RATE CLB, THE ACFT WAS DISPLAYING SOME ERRATIC PRESSURIZATION RATE INDICATIONS. WE WERE WORKING AT MAINTAINING PROPER PRESSURIZATION RATE THROUGH THE CLB AND REALIZED THAT THE AIRPLANE WAS NOT GOING TO PRESSURIZE NORMALLY. USING MANUAL PRESSURIZATION CTL, BACKED UP WITH OUR CHKLIST FOR AUTOMATIC PRESSURE CTL FAILURE, WE WERE ABLE TO MAINTAIN SOME RATE CTL. WE WERE ASSIGNED A HIGHER ALT AND A CREW DECISION WAS MADE TO DISCONTINUE THE CLB, TERMINATE THE FLT AND RETURN HOME. WE STOPPED THE CLB BTWN FL290 AND FL300. A REQUEST WAS MADE FOR A LOWER ALT AND TO RETURN TO OUR POINT OF DEP, WHICH WAS GRANTED BY ATC. WE WERE ASSIGNED FL280 AND HDG 270 DEGS A R TURN OF ABOUT 30 DEGS. A DSCNT WAS STARTED IN AN EFFORT TO REGAIN ANY CTL OVER THE PRESSURIZATION AND BRING THE CABIN TO A SAFE ALT, ANTICIPATING NO DELAYS IN DSCNT. ATC INQUIRED ABOUT OUR DSCNT REQUEST AND FLT PLAN CHANGE AND WE ADVISED THEM OF OUR PRESSURIZATION PROB AND REQUESTED EVEN LOWER. IN THE CONTINUED EFFORT TO REGAIN PRESSURIZATION CTL, WE DSNDED BELOW OUR ASSIGNED ALT OF FL280. WE WERE ASSIGNED FL240, BUT THE PRESSURIZATION PROB WOULD NOT ALLOW US TO HOLD FL240 AND THE DSCNT WAS CONTINUED, ALONG WITH AN ADDITIONAL REQUEST FOR A LOWER ALT. ATC GRANTED OUR REQUEST FOR LOWER AND WE WERE ASSIGNED 15000 FT AND A NEW ATC FREQ. UPON THE RADIO CHANGE, WE WERE ASSIGNED 11000 FT AND LEVELED AT THAT ALT WITH THE NEW CTLR. IT WAS AT THIS ALT THE PRESSURIZATION RATE WAS NO LONGER A PROB. WE WERE SWITCHED TO BATTLE CREEK APCH, WHICH GRANTED US A HOLD AT 7000 FT TO ASSESS OUR SIT AND REDUCE OUR FUEL LOAD. WE HELD FOR APPROX 45 MINS THEN RETURNED TO OUR POINT OF DEP AND LANDED WITHOUT INCIDENT. AFTER REVIEW OF THE SIT BY THE CREW, A STOP OF THE CLB SOONER WOULD HAVE LESSENED THE URGENCY FOR DSCNT AND REDUCED THE EFFECTS OF ANY PRESSURIZATION 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.