ACR LGT ACFT NOSE GEAR SAFETY PIN LEFT INSTALLED DURING TKOF RESULTING IN A RETURN LAND.

Narrative

AFTER A REDUCED REST LAYOVER IN MIAMI WE DEPARTED MIA FOR HOUSTON. AFTER TKOF THE GEAR WAS RETRACTED BUT THE INDICATION WAS OUR NOSE GEAR WAS NOT IN THE UP AND LOCKED POS. WE DETERMINED THAT THERE MIGHT BE A PROB WITH THE NOSE GEAR (OVER SVCED STRUT; ETC) AND DECIDED TO RETURN FOR LNDG. A NORMAL LNDG WAS MADE WITH A NORMAL TAXI-IN TO THE GATE. AFTER PARKING AT THE GATE MAINT DISCOVERED THAT THE NOSE GEAR PIN WAS INSTALLED AND THAT PREVENTED THE NOSE GEAR FROM BEING RETRACTED. I (FE) TOLD THE CAPT THAT DURING MY PREFLT INSPECTION I DID NOT SEE THE FLAG FROM THE NOSE GEAR PIN HANGING DOWN WHEN I LOOKED UP THE NOSE GEAR WELL. I ALSO TOLD HIM THAT I DID NOT PHYSICALLY CHK THE STOWED GEAR PINS DURING MY COCKPIT INSPECTION. I ASSUMED THAT SINCE THIS ACFT SAT AT THE GATE ALL NIGHT AND THE SOP FOR MAINT WHEN PINNING THE GEAR IS TO WRITE IT UP IN THE ACFT LOG (THERE WAS NO WRITE-UP); I WAS SAFE TO ASSUME ALL 3 PINS WERE STOWED. I GUESS I BECAME COMPLACENT ABOUT THE PREFLT CHK OF THE GEAR PINS BECAUSE THIS HAS NEVER HAPPENED BEFORE. I LEARNED THAT YOU CAN'T TRUST ANYONE BUT YOURSELF TO DO THE JOB RIGHT!