B737-300 flight crew over-pressurizes the aircraft during a ferry flight.

Attributes
ACN	723823
Time
Date	200701
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : zzz.artcc
State Reference	US
Altitude	msl single value : 20000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zzz.artcc
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 91
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 244 flight time type : 7300
ASRS Report	723823
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Experience	flight time last 90 days : 247 flight time type : 1050
Events
Anomaly	maintenance problem : improper documentation
Independent Detector	aircraft equipment other aircraft equipment : cabin press ctlr other flight crewa other flight crewb
Resolutory Action	none taken : anomaly accepted
Consequence	other
Supplementary
Problem Areas	Company Flight Crew Human Performance Maintenance Human Performance
Primary Problem	Ambiguous

Narrative:

I was assigned to ferry aircraft X from mdw for reposition to fix skin cracks. I received information with my release paperwork and was briefed by dispatch that they had planned this flight at FL200 because of pressurization limitations. Dispatch informed me in the phone brief that the aircraft could be pressurized up to 4.0 cabin pressure; and that FL260 was the approximately maximum altitude with a 3.9 cabin pressure. I was included in a 3-WAY call with the chief pilot on call. After inspection of the fuselage and informing the dispatcher and the chief pilot on call that I was comfortable taking the jet at the briefed altitude; I referenced the pressurization placard on the pressurization panel on the jet. It confirmed that the cabin pressure at FL260 would be 3.9. As we climbed out to FL200; we noticed the pressurization differential above 7.0; but the cabin was still at 1.9. After leveloff; I contacted dispatch and maintenance to confirm those readings as what we wanted. Both confirmed with us the readings as acceptable. I also had a mechanic onboard who confirmed for us that we wanted no more than 4.0 on the cabin pressure reading. Later on in the flight; we were contacted via voice by dispatch to report our pressure readings. At this point there was confusion as to which readings we were to follow. I reported again the inner pointer reading of 1.9; and dispatch said we needed to decrease the cabin pressure differential by setting a higher reading in the cruise altitude window. We then lost voice communication with dispatch. Later we were contacted by dispatch via ACARS and told; per maintenance and the chief pilot; to decrease the pressure differential. I asked how they wanted me to do this and I was told to 'control the outflow valve.' I was confused as to what they wanted since the outflow valve was working perfectly and holding the desired cabin pressure. At this point we encountered turbulent air and icing; and had to descend to 16000 ft. The pressurization decreased per schedule to below 4.0 differential on the descent. I asked 3 mechanics how I could have done this better; and all 3 told me I had done the correct procedures.

Original NASA ASRS Text

Title: B737-300 FLT CREW OVER-PRESSURIZES THE ACFT DURING A FERRY FLT.

Narrative: I WAS ASSIGNED TO FERRY ACFT X FROM MDW FOR REPOSITION TO FIX SKIN CRACKS. I RECEIVED INFORMATION WITH MY RELEASE PAPERWORK AND WAS BRIEFED BY DISPATCH THAT THEY HAD PLANNED THIS FLT AT FL200 BECAUSE OF PRESSURIZATION LIMITATIONS. DISPATCH INFORMED ME IN THE PHONE BRIEF THAT THE ACFT COULD BE PRESSURIZED UP TO 4.0 CABIN PRESSURE; AND THAT FL260 WAS THE APPROX MAX ALT WITH A 3.9 CABIN PRESSURE. I WAS INCLUDED IN A 3-WAY CALL WITH THE CHIEF PLT ON CALL. AFTER INSPECTION OF THE FUSELAGE AND INFORMING THE DISPATCHER AND THE CHIEF PLT ON CALL THAT I WAS COMFORTABLE TAKING THE JET AT THE BRIEFED ALT; I REFED THE PRESSURIZATION PLACARD ON THE PRESSURIZATION PANEL ON THE JET. IT CONFIRMED THAT THE CABIN PRESSURE AT FL260 WOULD BE 3.9. AS WE CLBED OUT TO FL200; WE NOTICED THE PRESSURIZATION DIFFERENTIAL ABOVE 7.0; BUT THE CABIN WAS STILL AT 1.9. AFTER LEVELOFF; I CONTACTED DISPATCH AND MAINT TO CONFIRM THOSE READINGS AS WHAT WE WANTED. BOTH CONFIRMED WITH US THE READINGS AS ACCEPTABLE. I ALSO HAD A MECH ONBOARD WHO CONFIRMED FOR US THAT WE WANTED NO MORE THAN 4.0 ON THE CABIN PRESSURE READING. LATER ON IN THE FLT; WE WERE CONTACTED VIA VOICE BY DISPATCH TO RPT OUR PRESSURE READINGS. AT THIS POINT THERE WAS CONFUSION AS TO WHICH READINGS WE WERE TO FOLLOW. I RPTED AGAIN THE INNER POINTER READING OF 1.9; AND DISPATCH SAID WE NEEDED TO DECREASE THE CABIN PRESSURE DIFFERENTIAL BY SETTING A HIGHER READING IN THE CRUISE ALT WINDOW. WE THEN LOST VOICE COM WITH DISPATCH. LATER WE WERE CONTACTED BY DISPATCH VIA ACARS AND TOLD; PER MAINT AND THE CHIEF PLT; TO DECREASE THE PRESSURE DIFFERENTIAL. I ASKED HOW THEY WANTED ME TO DO THIS AND I WAS TOLD TO 'CTL THE OUTFLOW VALVE.' I WAS CONFUSED AS TO WHAT THEY WANTED SINCE THE OUTFLOW VALVE WAS WORKING PERFECTLY AND HOLDING THE DESIRED CABIN PRESSURE. AT THIS POINT WE ENCOUNTERED TURBULENT AIR AND ICING; AND HAD TO DSND TO 16000 FT. THE PRESSURIZATION DECREASED PER SCHEDULE TO BELOW 4.0 DIFFERENTIAL ON THE DSCNT. I ASKED 3 MECHS HOW I COULD HAVE DONE THIS BETTER; AND ALL 3 TOLD ME I HAD DONE THE CORRECT PROCS.

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.