FLC OF AN MDT RETURNED TO LAND AFTER THE LNDG GEAR FAILED TO RETRACT DUE TO THE SAFETY PIN LEFT IN.

Narrative

MY CAPT WAS REVIEWING OUR RELEASE AND I VOLUNTEERED TO PREFLT THE ACFT. NORMALLY THERE ARE PROP TETHERS; ENG INTAKE PLUGS; GEAR PINS; AND A NOSEWHEEL LOCK ON THE AIRPLANE FROM THE SECURING BY THE CREW THE NIGHT BEFORE. I USUALLY WORK AT MANY BASES BEING ON THE DASH 8 RESERVE SYS AND WAS NOT USED TO THESE PIECES OF EQUIP BEING REMOVED BY RAMP PERSONNEL. YET THIS MORNING THE PROP TETHERS; PLUGS AND NOSE LOCK WERE ALL REMOVED. THE GEAR PIN FLAG ON THE #2 GEAR WAS GONE AND THE WARNING FLAG OF THE #1 GEAR PIN WAS UP IN THE WHEELWELL. WHEN I PREFLTED THE ACFT I VISUALLY LOOKED FOR THESE FLAGS BUT DID NOT CHK THE GEAR PIN HOLE ITSELF FOR OBSTRUCTIONS. THE CHKLIST WAS PERFORMED AND I CONTINUED UNDER THE ASSUMPTION THAT ALL SECURING EQUIP WAS REMOVED. THE CAPT AND I CONTINUED THROUGH TKOF WHERE OUR MAIN GEAR DID NOT CYCLE UP. WE RETURNED THE GEAR TO ITS DOWN POS REQUEST TO CIRCLE. FOLLOWED THE APPROPRIATE CHKLISTS AND RETURNED TO OUR GATE. THIS OCCURRENCE HAS HAPPENED TO OVER 3 DIFFERENT CREWS IN THE LAST 10 MONTHS. THE COMPANY IS PRESENTLY NEGOTIATING A CONTRACT AND THIS TIME HAS SUBMITTED AN INCIDENT RPT. A VIOLATION IS PENDING ON MY CAPT. HE HAS SUBMITTED A NASA FORM AS WELL. WE HAVE LEARNED THAT A DOUBLE XCHK IS IMPERATIVE; AND FROM THIS POOR EXPERIENCE I AM SURE WE WILL BE VERY CONSCIOUS OF THE GEAR PINS DURING PREFLT IN THE FUTURE.