Air carrier widebody transport unable maintain pressurization on climb started return to departure s...

Attributes
ACN	84248
Time
Date	198803
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : trm
State Reference	CA
Altitude	msl bound lower : 31000 msl bound upper : 31000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zla
Operator	common carrier : air carrier
Make Model Name	Widebody, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 210 flight time total : 35000 flight time type : 2000
ASRS Report	84248
Person 2
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	aircraft equipment problem : less severe
Independent Detector	other flight crewa
Resolutory Action	flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	other

Narrative:

Flight departed lax with #1 pack inoperative and listed on MEL and filed for a cruise altitude of FL330. We expected the cabin altitude therefore to climb to a higher altitude than normal if both packs had been operable, so we were not concerned when it indicated 8000'. As it continued to climb past 9000', we stopped our climb and requested 29000'. The cabin continued to climb, so we asked for 25000'. The cabin had then reached 11000', so we asked for 10000' and clearance back to lax. We were given clearance to 12000' and direct tnp. In the process of running the abnormal checklist, we found the engine start switch in the arm position. When it was placed in the start abort position, the #2 pack returned to operation. All of the pack indications had been normal with the exception of the flow indicator, which we assumed was inoperative (it did not change when the pack came on). Pressurization then stabilized with the cabin at an altitude of 12500'. The oxygen masks in the cabin did not drop. Cabin then descended to 6000'. We did not declare an emergency, however I did not have time to re-emphasize that fact to the controller when I heard him say he was going to treat us as an emergency in order to get us down. No emergency descent was executed. Once everything had stabilized, we requested en route clearance to atl and continued west/O incident. No altitudes were infringed upon and all maneuvering was performed after receiving clearance to do so, but I did hear the controller put at least 1 aircraft on a vector in order to get us down through his altitude. (The controllers did a super job and were very helpful.) the culprit switch should have been placed to start abort prior to taxi (and was answered for on the before taxi checklist). Its position, however, was apparently misread. That, along with the inoperative pack and gauge, led us into the pressurization problem.

Original NASA ASRS Text

Title: ACR WDB UNABLE MAINTAIN PRESSURIZATION ON CLIMB STARTED RETURN TO DEP STATION AND DESCENDED, THEN FOUND SWITCH IN WRONG POSITION CAUSED PROBLEM AND RESUMED FLT.

Narrative: FLT DEPARTED LAX WITH #1 PACK INOP AND LISTED ON MEL AND FILED FOR A CRUISE ALT OF FL330. WE EXPECTED THE CABIN ALT THEREFORE TO CLB TO A HIGHER ALT THAN NORMAL IF BOTH PACKS HAD BEEN OPERABLE, SO WE WERE NOT CONCERNED WHEN IT INDICATED 8000'. AS IT CONTINUED TO CLB PAST 9000', WE STOPPED OUR CLB AND REQUESTED 29000'. THE CABIN CONTINUED TO CLB, SO WE ASKED FOR 25000'. THE CABIN HAD THEN REACHED 11000', SO WE ASKED FOR 10000' AND CLRNC BACK TO LAX. WE WERE GIVEN CLRNC TO 12000' AND DIRECT TNP. IN THE PROCESS OF RUNNING THE ABNORMAL CHKLIST, WE FOUND THE ENG START SWITCH IN THE ARM POS. WHEN IT WAS PLACED IN THE START ABORT POS, THE #2 PACK RETURNED TO OPERATION. ALL OF THE PACK INDICATIONS HAD BEEN NORMAL WITH THE EXCEPTION OF THE FLOW INDICATOR, WHICH WE ASSUMED WAS INOP (IT DID NOT CHANGE WHEN THE PACK CAME ON). PRESSURIZATION THEN STABILIZED WITH THE CABIN AT AN ALT OF 12500'. THE OXYGEN MASKS IN THE CABIN DID NOT DROP. CABIN THEN DSNDED TO 6000'. WE DID NOT DECLARE AN EMER, HOWEVER I DID NOT HAVE TIME TO RE-EMPHASIZE THAT FACT TO THE CTLR WHEN I HEARD HIM SAY HE WAS GOING TO TREAT US AS AN EMER IN ORDER TO GET US DOWN. NO EMER DSCNT WAS EXECUTED. ONCE EVERYTHING HAD STABILIZED, WE REQUESTED ENRTE CLRNC TO ATL AND CONTINUED W/O INCIDENT. NO ALTS WERE INFRINGED UPON AND ALL MANEUVERING WAS PERFORMED AFTER RECEIVING CLRNC TO DO SO, BUT I DID HEAR THE CTLR PUT AT LEAST 1 ACFT ON A VECTOR IN ORDER TO GET US DOWN THROUGH HIS ALT. (THE CTLRS DID A SUPER JOB AND WERE VERY HELPFUL.) THE CULPRIT SWITCH SHOULD HAVE BEEN PLACED TO START ABORT PRIOR TO TAXI (AND WAS ANSWERED FOR ON THE BEFORE TAXI CHKLIST). ITS POS, HOWEVER, WAS APPARENTLY MISREAD. THAT, ALONG WITH THE INOP PACK AND GAUGE, LED US INTO THE PRESSURIZATION PROB.

Data retrieved from NASA's ASRS site as of August 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.

Air carrier widebody transport unable maintain pressurization on climb started return to departure station and descended, then found switch in wrong position caused problem and resumed flight.