A mechanic reports he unknowingly; installed a fan bypass check valve 180 degrees out in the diffuse...

Narrative:

Took over a primary heat exchanger replacement job; right-hand pack on a B737-800. There was a non-routine for a cracked plenum. When we took over the job; the previous workers were gone and all the parts were on a table disassembled. The new part arrived. The amm we used was XXX. On page X; step G (X); (a) thru (c) does not 'note' the proper positioning of the fan bypass check valve in the plenum. Also; the figures (drawings) for the plenum/diffuser assembly; figure XXX; sheet 1 & 2; show that it is 'murphy proof'; and cannot be installed upside down; or 180 degrees out. On figure XXX sheet 2; there is no forward; aft; left-hand assembly; right-hand assembly identifications. We installed the assembly as to what we assumed was the proper way per the amm and the our work card. It was found out later due to right-hand pack problems; that the fan bypass check valve was installed 180 degrees out in the diffuser assembly. I feel that the amm and the figure should be clarified to show and tell you more info on how the diffuser should be installed onto the plenum.

Original NASA ASRS Text

Title: A Mechanic reports he unknowingly; installed a Fan Bypass Check valve 180 degrees out in the Diffuser/ Plenum assembly; for the Right-hand Pack; on a B737-800; even though the AMM shows the Check valve is 'Murphy Proof'; and cannot be installed upside down or 180 degrees out.

Narrative: Took over a Primary Heat Exchanger replacement job; Right-hand Pack on a B737-800. There was a Non-Routine for a cracked Plenum. When we took over the job; the previous workers were gone and all the parts were on a table disassembled. The new part arrived. The AMM we used was XXX. On page X; step G (X); (a) thru (c) does not 'Note' the proper positioning of the Fan Bypass Check Valve in the Plenum. Also; the Figures (Drawings) for the Plenum/Diffuser assembly; figure XXX; sheet 1 & 2; show that it is 'Murphy Proof'; and cannot be installed upside down; or 180 degrees out. On Figure XXX sheet 2; there is no Forward; Aft; Left-hand Assembly; Right-hand Assembly identifications. We installed the assembly as to what we assumed was the proper way per the AMM and the our Work Card. It was found out later due to Right-hand Pack problems; that the Fan Bypass Check Valve was installed 180 degrees out in the Diffuser assembly. I feel that the AMM and the Figure should be clarified to show and tell you more info on how the Diffuser should be installed onto the Plenum.

Data retrieved from NASA's ASRS site as of April 2012 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	857197
Time
Date	200910
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Light	Daylight
Aircraft 1
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	Parked
Component
Aircraft Component	Air Conditioning Distribution System
Person 1
Function	Technician
Qualification	Maintenance Powerplant Maintenance Airframe
Experience	Maintenance Technician 26
Events
Anomaly	Aircraft Equipment Problem Critical

A mechanic reports he unknowingly; installed a fan bypass check valve 180 degrees out in the diffuser/ plenum assembly; for the right-hand pack; on a B737-800; even though the amm shows the check valve is 'murphy proof'; and cannot be installed upside down or 180 degrees out.