Narrative:

A team of 4 technicians were performing work card engineering authority/authorized XXXX; revision 'a;' for our first time. The WX was a massive thunderstorm with high winds and rain. The location was on the 'B' check pad dark up on a lift truck. The paperwork was confusing on the slat position to perform the work. The reference material at figure 023 was misleading of the sensor target remove and to be installed. It took 4 technicians to remove and install the bearings and targets (washers); 2 applying pressure to the slats and 2 to install the bearing and align the bolts and targets. I was unable to see the target removed or installed from the position I was at applying pressure to the slat. The 2 technicians removing and installing the bearings and targets were XXX and YYY. The other technician applying pressure was ZZZ. During all the WX conditions; the 2 technicians somehow installed the targets in the opposite position. I checked the correct torque on the bolts; and verified the correct gap between the sensors and targets; 'a' system test 767-400 amm 27-81-02/501 was performed and passed by XXX. (The aircraft experienced a slat asymmetry indication on a subsequent flight and returned to the departure airport.)

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Original NASA ASRS Text

Title: A B767-400 RETURNED TO THE FIELD DUE TO SLAT ASYMMETRY INDICATION AND WARNING. CAUSED BY INCORRECT INSTALLATION OF SLAT POS SENSOR TARGETS.

Narrative: A TEAM OF 4 TECHNICIANS WERE PERFORMING WORK CARD ENGINEERING AUTH XXXX; REVISION 'A;' FOR OUR FIRST TIME. THE WX WAS A MASSIVE TSTM WITH HIGH WINDS AND RAIN. THE LOCATION WAS ON THE 'B' CHK PAD DARK UP ON A LIFT TRUCK. THE PAPERWORK WAS CONFUSING ON THE SLAT POS TO PERFORM THE WORK. THE REF MATERIAL AT FIGURE 023 WAS MISLEADING OF THE SENSOR TARGET REMOVE AND TO BE INSTALLED. IT TOOK 4 TECHNICIANS TO REMOVE AND INSTALL THE BEARINGS AND TARGETS (WASHERS); 2 APPLYING PRESSURE TO THE SLATS AND 2 TO INSTALL THE BEARING AND ALIGN THE BOLTS AND TARGETS. I WAS UNABLE TO SEE THE TARGET REMOVED OR INSTALLED FROM THE POS I WAS AT APPLYING PRESSURE TO THE SLAT. THE 2 TECHNICIANS REMOVING AND INSTALLING THE BEARINGS AND TARGETS WERE XXX AND YYY. THE OTHER TECHNICIAN APPLYING PRESSURE WAS ZZZ. DURING ALL THE WX CONDITIONS; THE 2 TECHNICIANS SOMEHOW INSTALLED THE TARGETS IN THE OPPOSITE POS. I CHKED THE CORRECT TORQUE ON THE BOLTS; AND VERIFIED THE CORRECT GAP BTWN THE SENSORS AND TARGETS; 'A' SYS TEST 767-400 AMM 27-81-02/501 WAS PERFORMED AND PASSED BY XXX. (THE ACFT EXPERIENCED A SLAT ASYMMETRY INDICATION ON A SUBSEQUENT FLT AND RETURNED TO THE DEP ARPT.)

Data retrieved from NASA's ASRS site as of January 2009 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.