Flight crew of air carrier medium large transport unable to control pressurization after takeoff from tvl. Horn sounded, masks dropped, emergency declared, and aircraft descended as cleared.

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Attributes
ACN	87884
Time
Date	198805
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : tvl
State Reference	CA
Altitude	msl bound lower : 20000 msl bound upper : 24000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zoa tower : pdk
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	climbout : intermediate altitude cruise other descent other
Route In Use	enroute : direct enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : commercial pilot : instrument pilot : atp
Experience	flight time last 90 days : 120 flight time total : 13000 flight time type : 1500
ASRS Report	87884
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : atp
Experience	flight time last 90 days : 70 flight time total : 7500 flight time type : 500
ASRS Report	88335
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : declared emergency none taken : unable other
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

After departing tvl with 31 passengers on board, leveled flight at FL240. Center cleared us to modesto then the mod arrival to sfo. We started experiencing slow fluctuations in the pressurization. We switched to the standby mode which seemed to control the problem, in a couple of minutes the cabin started rapid fluctuations and we informed center that we were having a pressurization problem and we were requesting lower, the cabin pressurization horn came on and we immediately declared an emergency and requested lower while we started the emergency checklist. Center responded with 'you are cleared to FL200, turn right to 270 degree', vector for traffic and then gave us a frequency change. We rather hurriedly did what we were told as we started our emergency descent. The new controller told us to level off at FL200. I talked with the flight attendants and they assured me all the passengers were calm and on oxygen. At this time I had a decision to make. I knew we were stable and under control at FL200, center knew we had an emergency, and yet he wanted us level at FL200. My present condition was a lot less traumatic than a midair collision. In a couple of minutes, center cleared us down, the emergency was over and we continued to sfo.

Original NASA ASRS Text

Title: FLT CREW OF ACR MLG UNABLE TO CONTROL PRESSURIZATION AFTER TKOF FROM TVL. HORN SOUNDED, MASKS DROPPED, EMERGENCY DECLARED, AND ACFT DESCENDED AS CLEARED.

Narrative: AFTER DEPARTING TVL WITH 31 PASSENGERS ON BOARD, LEVELED FLT AT FL240. CENTER CLRED US TO MODESTO THEN THE MOD ARRIVAL TO SFO. WE STARTED EXPERIENCING SLOW FLUCTUATIONS IN THE PRESSURIZATION. WE SWITCHED TO THE STANDBY MODE WHICH SEEMED TO CONTROL THE PROBLEM, IN A COUPLE OF MINUTES THE CABIN STARTED RAPID FLUCTUATIONS AND WE INFORMED CENTER THAT WE WERE HAVING A PRESSURIZATION PROBLEM AND WE WERE REQUESTING LOWER, THE CABIN PRESSURIZATION HORN CAME ON AND WE IMMEDIATELY DECLARED AN EMER AND REQUESTED LOWER WHILE WE STARTED THE EMER CHECKLIST. CENTER RESPONDED WITH 'YOU ARE CLRED TO FL200, TURN RIGHT TO 270 DEG', VECTOR FOR TFC AND THEN GAVE US A FREQ CHANGE. WE RATHER HURRIEDLY DID WHAT WE WERE TOLD AS WE STARTED OUR EMER DESCENT. THE NEW CTLR TOLD US TO LEVEL OFF AT FL200. I TALKED WITH THE FLT ATTENDANTS AND THEY ASSURED ME ALL THE PASSENGERS WERE CALM AND ON OXYGEN. AT THIS TIME I HAD A DECISION TO MAKE. I KNEW WE WERE STABLE AND UNDER CTL AT FL200, CENTER KNEW WE HAD AN EMER, AND YET HE WANTED US LEVEL AT FL200. MY PRESENT CONDITION WAS A LOT LESS TRAUMATIC THAN A MIDAIR COLLISION. IN A COUPLE OF MINUTES, CENTER CLRED US DOWN, THE EMER WAS OVER AND WE CONTINUED TO SFO.

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.