Flight returned to airport with pressurization difficulties. Mechanic found the flow multiplier bypa...

Attributes
ACN	324852
Time
Date	199512
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : den
State Reference	CO
Altitude	agl bound lower : 0 agl bound upper : 0
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	ground : preflight
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	other personnel other
Qualification	other other : other
ASRS Report	324852
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	other flight crewa other other : unspecified
Resolutory Action	other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

On reference to air return of aircraft on morning of dec/wed/95. On return to gate, did a quick visual inspection of 2 lower cargo door seals and 2 forward east&east door seals for installation. On talking with flight crew they felt that the aft outflow valve was not closing all the way. Also asked if the flight attendants had noticed any noise leaking around the 4 cabin doors, none was reported. Checked outflow valve operation using standby/manual AC/dc modes, operation was normal. Also checked operation of forward cargo valve operation which was also normal. On further investigation found that the flow multiplier bypass shutoff valve was stuck in the closed position. Disconnected cannon plug and cleaned, reinstalled, valve started working. Ran engines and APU on gate. Pressurized aircraft to approximately 4 psi. Did not do a decay leakage test. Upon discussing situation with supervisor (mr X) who was there with me, we felt we had found the problem with the bypass valve. I released the aircraft for flight.

Original NASA ASRS Text

Title: FLT RETURNED TO ARPT WITH PRESSURIZATION DIFFICULTIES. MECH FOUND THE FLOW MULTIPLIER BYPASS SHUTOFF VALVE WAS STUCK IN THE CLOSED POS. CLEANED CANNON PLUG AND CORRECTED PROB.

Narrative: ON REF TO AIR RETURN OF ACFT ON MORNING OF DEC/WED/95. ON RETURN TO GATE, DID A QUICK VISUAL INSPECTION OF 2 LOWER CARGO DOOR SEALS AND 2 FORWARD E&E DOOR SEALS FOR INSTALLATION. ON TALKING WITH FLC THEY FELT THAT THE AFT OUTFLOW VALVE WAS NOT CLOSING ALL THE WAY. ALSO ASKED IF THE FLT ATTENDANTS HAD NOTICED ANY NOISE LEAKING AROUND THE 4 CABIN DOORS, NONE WAS RPTED. CHKED OUTFLOW VALVE OP USING STANDBY/MANUAL AC/DC MODES, OP WAS NORMAL. ALSO CHKED OP OF FORWARD CARGO VALVE OP WHICH WAS ALSO NORMAL. ON FURTHER INVESTIGATION FOUND THAT THE FLOW MULTIPLIER BYPASS SHUTOFF VALVE WAS STUCK IN THE CLOSED POS. DISCONNECTED CANNON PLUG AND CLEANED, REINSTALLED, VALVE STARTED WORKING. RAN ENGS AND APU ON GATE. PRESSURIZED ACFT TO APPROX 4 PSI. DID NOT DO A DECAY LEAKAGE TEST. UPON DISCUSSING SIT WITH SUPVR (MR X) WHO WAS THERE WITH ME, WE FELT WE HAD FOUND THE PROB WITH THE BYPASS VALVE. I RELEASED THE ACFT FOR FLT.

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.

Flight returned to airport with pressurization difficulties. Mechanic found the flow multiplier bypass shutoff valve was stuck in the closed position. Cleaned cannon plug and corrected problem.