Air carrier medium large transport returns land account a malfunction pressurization unit. Precautio...

Attributes
ACN	158907
Time
Date	199009
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : mdw
State Reference	IL
Altitude	msl bound lower : 10600 msl bound upper : 10600
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zau
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
Route In Use	departure other enroute airway : zau
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 200 flight time total : 6000 flight time type : 600
ASRS Report	158908
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	other
Consequence	Other Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Cabin pressure was not maintained. As I was flying I noticed on the glareshield the red master warning light on. I looked on the overhead panel master caution system and saw the message 'cabin altitude.' I called this to the attention of the captain who was in the process of accomplishing the climb checklist. At this point I disconnected the autoplt and leveled at 10600'. At some point after level-off the captain closed the outflow valve to regain the cabin to normal altitude for this altitude. We decided to return to mdw. Center gave us a clearance back and a lower altitude at this time. The F/a called 2-3 times during the first 2 mins after the problem was noticed wanting to know what was going on and letting us know that they were aware and what was going on in the cabin. I flew back descending at 500 FPM to mdw, while the captain answered radio calls and coordinated with our company about the return. He also operated the pressurization in the manual mode. After arrival at the gate 10-20 passenger went to see paramedics about ear pain. Flight was en route from mdw to lax. Primary automatic pressurization unit was replaced and the flight continued to lax 2 hours later. Note: cabin never exceeded 10000', no mask, horns, etc.

Original NASA ASRS Text

Title: ACR MLG RETURNS LAND ACCOUNT A MALFUNCTION PRESSURIZATION UNIT. PRECAUTIONARY DESCENT AND LNDG NOT CLASSIFIED AS EMERGENCY AS ALT WAS LOW ENOUGH TO HANDLE SITUATION.

Narrative: CABIN PRESSURE WAS NOT MAINTAINED. AS I WAS FLYING I NOTICED ON THE GLARESHIELD THE RED MASTER WARNING LIGHT ON. I LOOKED ON THE OVERHEAD PANEL MASTER CAUTION SYS AND SAW THE MESSAGE 'CABIN ALT.' I CALLED THIS TO THE ATTN OF THE CAPT WHO WAS IN THE PROCESS OF ACCOMPLISHING THE CLB CHKLIST. AT THIS POINT I DISCONNECTED THE AUTOPLT AND LEVELED AT 10600'. AT SOME POINT AFTER LEVEL-OFF THE CAPT CLOSED THE OUTFLOW VALVE TO REGAIN THE CABIN TO NORMAL ALT FOR THIS ALT. WE DECIDED TO RETURN TO MDW. CENTER GAVE US A CLRNC BACK AND A LOWER ALT AT THIS TIME. THE F/A CALLED 2-3 TIMES DURING THE FIRST 2 MINS AFTER THE PROB WAS NOTICED WANTING TO KNOW WHAT WAS GOING ON AND LETTING US KNOW THAT THEY WERE AWARE AND WHAT WAS GOING ON IN THE CABIN. I FLEW BACK DSNDING AT 500 FPM TO MDW, WHILE THE CAPT ANSWERED RADIO CALLS AND COORDINATED WITH OUR COMPANY ABOUT THE RETURN. HE ALSO OPERATED THE PRESSURIZATION IN THE MANUAL MODE. AFTER ARR AT THE GATE 10-20 PAX WENT TO SEE PARAMEDICS ABOUT EAR PAIN. FLT WAS ENRTE FROM MDW TO LAX. PRIMARY AUTO PRESSURIZATION UNIT WAS REPLACED AND THE FLT CONTINUED TO LAX 2 HRS LATER. NOTE: CABIN NEVER EXCEEDED 10000', NO MASK, HORNS, ETC.

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.

Air carrier medium large transport returns land account a malfunction pressurization unit. Precautionary descent and landing not classified as emergency as altitude was low enough to handle situation.