Air carrier medium large transport started an emergency descent to correct a minor pressurization pr...

Attributes
ACN	137152
Time
Date	199002
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : tul
State Reference	OK
Altitude	msl bound lower : 35000 msl bound upper : 35000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zfw
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Route In Use	enroute airway : zfw
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 270 flight time total : 13000 flight time type : 3000
ASRS Report	137152
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : overcame equipment problem flight crew : declared emergency
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

The warning horn indicating cabin altitude exceeding 10000' MSL came on while cruising at FL350. Before I could silence the horn and analyze the problem (the cabin altitude read 11000' and a very slight climb) the first officer commenced and executed an emergency descent drill. Including throttles to idle, speed brakes out and squawk transponder code 7700. Exactly by the book. The aircraft was well out of FL350 before I could comprehend that an emergency descent was in progress. No discussion just down we go. What happened to crew coordination? I have no answer. I think what happened was just a response to a trained situation with a canned response. After all was said and done simple investigation revealed a failed pneumatic source (bleed valve) and a weak right air-conditioning pack. Simply opening the cross bleed would have solved the problem.

Original NASA ASRS Text

Title: ACR MLG STARTED AN EMERGENCY DESCENT TO CORRECT A MINOR PRESSURIZATION PROBLEM.

Narrative: THE WARNING HORN INDICATING CABIN ALT EXCEEDING 10000' MSL CAME ON WHILE CRUISING AT FL350. BEFORE I COULD SILENCE THE HORN AND ANALYZE THE PROB (THE CABIN ALT READ 11000' AND A VERY SLIGHT CLB) THE F/O COMMENCED AND EXECUTED AN EMER DSCNT DRILL. INCLUDING THROTTLES TO IDLE, SPD BRAKES OUT AND SQUAWK TRANSPONDER CODE 7700. EXACTLY BY THE BOOK. THE ACFT WAS WELL OUT OF FL350 BEFORE I COULD COMPREHEND THAT AN EMER DSCNT WAS IN PROGRESS. NO DISCUSSION JUST DOWN WE GO. WHAT HAPPENED TO CREW COORD? I HAVE NO ANSWER. I THINK WHAT HAPPENED WAS JUST A RESPONSE TO A TRAINED SITUATION WITH A CANNED RESPONSE. AFTER ALL WAS SAID AND DONE SIMPLE INVESTIGATION REVEALED A FAILED PNEUMATIC SOURCE (BLEED VALVE) AND A WEAK RIGHT AIR-CONDITIONING PACK. SIMPLY OPENING THE CROSS BLEED WOULD HAVE SOLVED THE 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.

Air carrier medium large transport started an emergency descent to correct a minor pressurization problem.