An air carrier mechanic reports that he failed to install a cannon plug properly on the pressurizati...

Narrative:

I was performing work card X 'check pressurization system' on an air carrier B737-200. I found that the outflow valve was not responding according to the work card which states 'operate manual toggle switch from center to closed/open position and check that valve position indicator shows a slight movement toward closed/open.' the valve position indicator was showing the valve moving all the way closed/open with the system in the flight mode on aircraft. So I checked the maintenance manual page 'pressurization control system -- adjustment/test' and found that it state the same thing for the valve movement as the work card. I continued to check the manual and found that the page stated 'move and hold the manual outflow valve toggle switch to open/closed and verify the valve moves toward the fully open/closed position in a smooth, continuous manner by observing the valve position indicator,' which is the way the aircraft was working. But the manual page had a note which stated, 'if a cabin pressure selector is installed, the outflow valve will move incrementally in the flight mode with each toggle switch actuation, the toggle switch must be cycled in order to fully close or open the outflow valve.' the work card X has no note as to the way the valve movement should be in regards to the type part number of the selector panel installed on the aircraft. So I tried to read the part number on the selector panel while it was installed, but was unable to find the part number, so I removed the panel and now I could see the part. It was not a part number, the panel was reinstalled and cannon plug reconnected. I determined that the system was working normally, but not the way the work card stated for the valve movement in the flight mode. I made a note on the work card that the valve was working normally for the type part number of selector panel. That morning the aircraft departed and the pressurization system worked normally till at or about 10000 ft. Then they developed pressurization problems. The aircraft returned to the gate and the mechanic found that the cannon plug on the pressurization control panel had come loose. He reinstalled it, but had to use pliers to get it reinstalled. The aircraft departed and the system worked normally.

Original NASA ASRS Text

Title: AN ACR MECH RPTS THAT HE FAILED TO INSTALL A CANNON PLUG PROPERLY ON THE PRESSURIZATION SYS OF AN ACR B737-200. THIS LED TO A RETURN LAND SIT WHEN THE ACFT WOULD NOT PRESSURIZE.

Narrative: I WAS PERFORMING WORK CARD X 'CHK PRESSURIZATION SYS' ON AN ACR B737-200. I FOUND THAT THE OUTFLOW VALVE WAS NOT RESPONDING ACCORDING TO THE WORK CARD WHICH STATES 'OPERATE MANUAL TOGGLE SWITCH FROM CTR TO CLOSED/OPEN POS AND CHK THAT VALVE POS INDICATOR SHOWS A SLIGHT MOVEMENT TOWARD CLOSED/OPEN.' THE VALVE POS INDICATOR WAS SHOWING THE VALVE MOVING ALL THE WAY CLOSED/OPEN WITH THE SYS IN THE FLT MODE ON ACFT. SO I CHKED THE MAINT MANUAL PAGE 'PRESSURIZATION CTL SYS -- ADJUSTMENT/TEST' AND FOUND THAT IT STATE THE SAME THING FOR THE VALVE MOVEMENT AS THE WORK CARD. I CONTINUED TO CHK THE MANUAL AND FOUND THAT THE PAGE STATED 'MOVE AND HOLD THE MANUAL OUTFLOW VALVE TOGGLE SWITCH TO OPEN/CLOSED AND VERIFY THE VALVE MOVES TOWARD THE FULLY OPEN/CLOSED POS IN A SMOOTH, CONTINUOUS MANNER BY OBSERVING THE VALVE POS INDICATOR,' WHICH IS THE WAY THE ACFT WAS WORKING. BUT THE MANUAL PAGE HAD A NOTE WHICH STATED, 'IF A CABIN PRESSURE SELECTOR IS INSTALLED, THE OUTFLOW VALVE WILL MOVE INCREMENTALLY IN THE FLT MODE WITH EACH TOGGLE SWITCH ACTUATION, THE TOGGLE SWITCH MUST BE CYCLED IN ORDER TO FULLY CLOSE OR OPEN THE OUTFLOW VALVE.' THE WORK CARD X HAS NO NOTE AS TO THE WAY THE VALVE MOVEMENT SHOULD BE IN REGARDS TO THE TYPE PART NUMBER OF THE SELECTOR PANEL INSTALLED ON THE ACFT. SO I TRIED TO READ THE PART NUMBER ON THE SELECTOR PANEL WHILE IT WAS INSTALLED, BUT WAS UNABLE TO FIND THE PART NUMBER, SO I REMOVED THE PANEL AND NOW I COULD SEE THE PART. IT WAS NOT A PART NUMBER, THE PANEL WAS REINSTALLED AND CANNON PLUG RECONNECTED. I DETERMINED THAT THE SYS WAS WORKING NORMALLY, BUT NOT THE WAY THE WORK CARD STATED FOR THE VALVE MOVEMENT IN THE FLT MODE. I MADE A NOTE ON THE WORK CARD THAT THE VALVE WAS WORKING NORMALLY FOR THE TYPE PART NUMBER OF SELECTOR PANEL. THAT MORNING THE ACFT DEPARTED AND THE PRESSURIZATION SYS WORKED NORMALLY TILL AT OR ABOUT 10000 FT. THEN THEY DEVELOPED PRESSURIZATION PROBS. THE ACFT RETURNED TO THE GATE AND THE MECH FOUND THAT THE CANNON PLUG ON THE PRESSURIZATION CTL PANEL HAD COME LOOSE. HE REINSTALLED IT, BUT HAD TO USE PLIERS TO GET IT REINSTALLED. THE ACFT DEPARTED AND THE SYS WORKED NORMALLY.

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.

Attributes
ACN	338894
Time
Date	199606
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : zzz
State Reference	US
Altitude	agl bound lower : 0 agl bound upper : 0
Environment
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B737-200
Operating Under FAR Part	Part 121
Flight Phase	ground : parked other
Person 1
Affiliation	company : air carrier
Function	other personnel other
Qualification	other other : other
ASRS Report	338894
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : critical non adherence : published procedure other anomaly other
Independent Detector	other other : unspecified
Resolutory Action	none taken : detected after the fact other
Consequence	Other
Supplementary
Air Traffic Incident	other

An air carrier mechanic reports that he failed to install a cannon plug properly on the pressurization system of an air carrier B737-200. This led to a return land situation when the aircraft would not pressurize.