A BEECH CRAFT 90 ON INITIAL CLB AT 1200 FT RETURNED TO THE FIELD DUE TO THE L ENG OIL COOLER FAIRING DEPARTED THE ACFT CAUSED BY FAIRING FASTENERS NOT SECURED.

Narrative

AT THE END OF A 12 HR DAY; I WAS PERFORMING ROUTINE MAINT. DURING ROUTINE MAINT; I NEGLECTED TO PROPERLY SECURE THE L-HAND OIL COOLER FAIRING. THE ACFT MADE A NORMAL TKOF. AT APPROX 1200 FT THE FAIRING DEPARTED THE ACFT. A SKYDIVER RIDING IN THE ACFT RPTED TO THE PLT THAT 'SOMETHING WHITE PASSED BY THE DOOR.' THE PLT RETURNED FOR AN UNEVENTFUL LNDG. UPON INSPECTION; I FOUND THE FAIRING HAD DEPARTED THE ACFT. NO DAMAGE WAS CAUSED. THE FASTENERS HAD VIBRATED LOOSE (NOT PROPERLY TIGHTENED). THIS WAS NOT DETECTED DURING PREFLT BY THE PLT. I REPLACED THE FAIRING AND RETURNED THE ACFT FOR SVC. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED WHEN CLOSING UP THE JOB ALL THE FASTENERS WERE PUT IN PLACE BY HAND AND JUST NEEDED TORQUING WHEN ASSIGNED ANOTHER 'HOT' JOB. THE RPTR SAID HE HAD ALL GOOD INTENTIONS OF RETURNING AND COMPLETING THE FAIRING INSTALLATION BUT WAS CONTINUOUSLY BEING INTERRUPTED WITH OTHER SMALL JOBS. THE RPTR SAID NO JOB CARD WAS WRITTEN UP TO TORQUE AND FINAL INSPECT THE FAIRING INSTALLATION. THE RPTR STATED AT THIS POINT IN TIME HE HAD BEEN WORKING FOR 12 HRS AND WAS TIRED.