FLC OF A JETSTREAM 3100 HEARD A LOUD THUMP DURING INITIAL CLB AFTER TKOF AND RETURNED TO LAND THINKING IT WAS PROBABLY A BIRD STRIKE. HOWEVER; IT WAS ONE OF THE ENG COWLINGS COMING OFF THE ACFT AND STRIKING THE HORIZ STABILIZER WHICH CAUSED A SLIGHT ERRATIC JERK OF THE CTL YOKE.

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AFTER DEP FROM FAT WE CLBED THROUGH 400 FT AGL AND BEGAN ACCELERATION TO NORMAL CLB SPD. AS WE REACHED APPROX 145 KTS; THERE WAS A LOUD THUMP. SUSPECTING A HVY BIRD STRIKE; WE CHOSE TO RETURN TO FAT TO HAVE THE ACFT CHKED. THERE WAS A SLIGHT ERRATIC JERK IN THE YOKE AS WE WERE RETURNING TO LAND. ONCE ON THE GND; IT WAS FOUND THAT THE R COWLING WAS TORN AWAY AND HAD WRAPPED AROUND THE LEADING EDGE OF THE R HORIZ STABILIZER. THIS CAUSED THE DISRUPTION OF AIRFLOW WHICH CAUSED THE JERKING MOTION IN THE FLT CTL. I WAS THE FLT OFFICER RESPONSIBLE FOR THE PREFLT. DURING MY PREFLT; I CHKED THE COWLING VISUALLY TO SEE THAT IT WAS FLUSH TO THE ENG. I ALSO CHKED THAT THE DZUS FASTENERS WERE IN PLACE AND FLUSH WITH THE SURFACE. IT WAS DARK DURING THIS PREFLT AND I WAS USING A FLASHLIGHT. I FOUND NOTHING ABNORMAL. DURING THE INVESTIGATIVE INTERVIEW WITH THE FAA; IT WAS FOUND THAT I WAS UNAWARE OF THE COWLING MARKING INDICATING THAT DZUS FASTENERS ARE IN PLACE. (LOCKED) THIS INDICATION WAS NOT COVERED IN TRAINING AND IS ALSO NOT CONSISTENTLY PRESENT ON ALL ACFT. SINCE THIS INCIDENT; I HAVE SPOKEN WITH OTHER FO'S WHO ARE ALSO UNAWARE OF THESE MARKINGS AND PREFLT IN THE SAME MANNER AS I DO. IT HAS SINCE BEEN DETERMINED THAT MAINT ATTACHED A NUMBER OF DZUS FASTENERS IN THE COWLING BUT FAILED TO ATTACH A NUMBER OF FASTENERS NEAR THE BOTTOM. THE AIRFLOW WAS ABLE TO LIFT; THEN RIP OFF THE COWLING. I BELIEVE THIS INCIDENT COULD BE PREVENTED FROM HAPPENING AGAIN IF ALIGNMENT MARKINGS ARE COVERED IN TRAINING; PLTS ARE TAUGHT TO RUN THEIR FINGERS ALONG REACHABLE FASTENERS; AND TO BANG ON THE COWLING IN AN ATTEMPT TO DISLODGE LOOSE FASTENERS. MAINT COULD HELP BY MAKING IT STANDARD PRACTICE NOT TO INSERT A FASTENER INTO THE COWLING UNLESS IT IS COMPLETELY FASTENED INTO THE LOCKED POS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT THE FAA DID INVESTIGATE THIS INCIDENT AND NOTIFIED HER THAT SHE WAS UNDER INVESTIGATION FOR POSSIBLE LACK OF PROPER PREFLT PROC. HOWEVER; SHE HAS HEARD OR RECEIVED NOTHING MORE AS YET; BUT BELIEVES THAT IT IS COMING SOON. THE COMPANY HAS CHANGED THE MAINT RELEASE TO INCLUDE AN ADDITIONAL INSPECTION REVIEW BY THE MECH PRIOR TO RELEASING THE ACFT TO THE LINE; OR GATE; TO HELP ELIMINATE THIS TYPE OF INCIDENT FROM HAPPENING IN THE FUTURE.