Regional Jet 200 ER/LR (CRJ200)
Flight Crew Air Transport Pilot (ATP)
Human-Machine Interface
Aircraft Equipment Problem Critical
Flight Crew Returned To Departure Airport; General Maintenance Action
Human Factors
We arrived at the aircraft in the morning and performed a detailed inspection. All the gear pins and the ADG safety pin were in the storage closet. We taxied out and took off from Runway 14. At positive rate FO called 'gear up' and we received a gear disagree warning and an indication that the left main gear was still down which was confirmed by the tower. I performed the QRH and notified ATC; Dispatch and Maintenance. We returned to land as directed by the QRH. When we arrived at the gate I inspected the left main gear and found a gear pin installed. I had no reason to suspect a pin was missed on the walk around because there were 4 in the storage closet. First of all; we should have done a more thorough detailed inspection. Secondly; If Maintenance installs pins and gives the A/C an Airworthiness signoff; they should be sure to pull the pins; maybe a checklist should be implemented for Maintenance if one is not already in use. Lastly; The Company should mandate that if a pin is installed by anyone on our A/C; it should be required to have a bright; clean flag.
CRJ200 Captain reports performing a preflight in the morning and noting three gear pins in the storage closet. After takeoff the left main gear will not retract. Upon returning a fourth gear pin is found installed in the left gear; without a flag attached.