A B757-200 ON TKOF ROLL HAD THE #2 ENG PYLON FAIRING DEPART THE ACFT DUE TO IMPROPER INSTALLATION.

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ON MAY/XA/99 ACT XYZ (B757-200) OUT OF ZZZ; ON TKOF ROLL; LOST #2 PYLON FAIRING 441AT. BOEING IPC 54-52-01-009A ITEM 335. ACFT CONTINUED TO SANTA BARBARA; CA; WITHOUT FURTHER INCIDENT. THE FOLLOWING IS A SYNOPSIS OF THE EVENTS THAT LED TO THIS INCIDENT. ON MAY/XA/99; LATE SHIFT MECH INSTALLED FAIRING 441AT AND SIGNED OFF JOB CARD. ON MAY/XA/99 I INSPECTED THE INSTALLATION OF FAIRING. THE LATCHES WERE SECURE AND THE FAIRING APPEARED TO BE PROPERLY INSTALLED. THE ACFT WAS RELEASED TO LINE MAINT FOR ENG RUNS AND FINAL CHKS. THE LINE MECHS ALSO PERFORMED A FINAL WALKAROUND CHK OF ACFT BEFORE RELEASING ACFT FOR SVC; AND FOUND NO DISCREPANCIES. ON MAY/XB/99 ACFT WAS ROUTED FOR SVC FOR A TRIP TO SANTA BARBARA; CA. ON TKOF ROLL; FAIRING 441AT APPARENTLY CAME OFF AND WAS RECOVERED BY AIRFIELD SAFETY PERSONNEL. I BELIEVE THE INEXPERIENCE OF THE INVOLVED MECH PLAYED A MAJOR ROLL IN THIS INCIDENT. THE FAIRING CAN BE INSTALLED BY A CONDITION CALLED FALSE LATCHING. INSPECTION OF THE INSTALLATION IN THIS CONDITION CANNOT BE REVEALED VISUALLY AS WELL AS PHYSICALLY. THE HOOK ON THE FRONT END OF THE FAIRING CAN BE ENGAGED AND THE LATCHES ON THE BACK END CAN STILL BE FALSE LATCHED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT HE MADE THE OVERALL CLOSE UP INSPECTION OF THE #2 ENG PYLON FAIRING AND FOUND ALL PANEL FASTENERS AND LATCHES SECURE. THE RPTR SAID THE 2 AFT HOOK LATCHES ON THE FAIRING 441AT APPEARED LOCKED. THE RPTR SAID THESE LATCHES HAVE NO INDICATOR PIN; WITNESS MARK OR HOLE IN THE FAIRING TO VISUALLY CHK FOR LOCKED CONDITION. THE RPTR STATED THE MAINT MANUAL HAS BEEN UPDATED TO ALERT THE INSTALLING TECHNICIAN TO THE FALSE LOCK CONDITION. THE RPTR SAID THAT WHILE THE MANUAL ALERT WARNS OF THE PROB IT DOES NOTHING TO REMEDY THE CAUSE.