A CRJ-900 aft cargo door handle appeared fully closed but was not in the fully locked position; causing the amber 'aft cargo door' to annunciate in flight. The pilot returned to the departure airport for a door inspection.

Narrative

On climbout at 11000 ft the amber aft cargo door message light illuminated. The crew immediately ran through the checklist and notified Dispatch. Dispatch computed a flight release at FL100 and the flight would need 9700 lbs (burn plus reserve and no alternate required) to complete the flight to ZZZ. Unfortunately; the crew only had 9000 FOB. Maintenance was consulted and they talked to the crew. The aircraft was achieving full pressurization. They had seen this same problem several times before and thought it was most likely the door was closed all the way but was not fully in the locked position; so we decided to return back to ZZZ to have the door inspected. The crew landed safely without further incident and no emergency was declared. Upon inspection; the maintenance suspicions were correct and the door was found to be fully closed but not in the fully locked position. This same problem has happened several times now and has been a big problem for us since we have flown the CRJ-900'S. There needs to be a better way to make sure the aft cargo door is in the fully locked position. In the CRJ-900 POM it states on the checklist that in this case if the aircraft is able to maintain full pressurization that the flight can continue on and no further action is required. The flight could have continued on up to FL340 but the crew felt it was safer to return to ZZZ. Perhaps a set of procedures to clear up any gray areas in this matter would be helpful and the flight department could give some guidance on whether it would want to have the crews continue to the destination or return to the origin.