Narrative:

On departure I experienced some roll so we confirmed that the flaps and led's were indicating up. The first officer commented that he remembered a couple units of rudder trim from the inbound flight. After putting in a couple units; the aircraft felt good enough to continue so we climbed out above 10;000 ft. After putting the autopilot on; I noticed a significant displacement in the yoke and realized the amount of trim required was not within acceptable limits. I wanted someone to look at the wings to see if a spoiler was stuck up; so I asked the flight attendant to see if there was a pilot on board in the back. She reported that there wasn't and asked if there was anything she could do. I asked her to look at the wing and she said that the 2 sides seemed different. She volunteered to take a picture which clearly indicated that the right inboard flap was not in the up position. We immediately slowed down since we had inadvertently exceeded the flap speed since we hadn't known it was down and I tried to get a hold of dispatch on VHF. I could only relay through ops to dispatch so I decided to head back to ZZZ and declare an emergency. I free texted dispatch of our intentions. We were below max landing weight and the landing distances looked fine for a trailing edge flap up landing. The passengers were kept informed and the flight attendants did a great job preparing for landing. We encountered some bumps on the approach and the asymmetry decrease requiring less trim. It was a smooth landing with normal breaking and the fire chief said the brakes were not excessively hot. We were told to park in the hanger area and I looked at the flap which appeared to be nearly up. I made a log entry that the flap had not retracted on takeoff. On the bus to the terminal I realized that I had not written up the inadvertent overspeed; so I called maintenance and informed them.

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Original NASA ASRS Text

Title: Air Carrier Captain discovers that a trailing edge flap has failed to fully retract after reaching cruise altitude and elects to return to departure airport for a TE flaps up landing after declaring an emergency.

Narrative: On departure I experienced some roll so we confirmed that the flaps and LED's were indicating up. The First Officer commented that he remembered a couple units of rudder trim from the inbound flight. After putting in a couple units; the aircraft felt good enough to continue so we climbed out above 10;000 FT. After putting the autopilot on; I noticed a significant displacement in the yoke and realized the amount of trim required was not within acceptable limits. I wanted someone to look at the wings to see if a spoiler was stuck up; so I asked the Flight Attendant to see if there was a pilot on board in the back. She reported that there wasn't and asked if there was anything she could do. I asked her to look at the wing and she said that the 2 sides seemed different. She volunteered to take a picture which clearly indicated that the right inboard flap was not in the up position. We immediately slowed down since we had inadvertently exceeded the flap speed since we hadn't known it was down and I tried to get a hold of Dispatch on VHF. I could only relay through Ops to Dispatch so I decided to head back to ZZZ and declare an emergency. I free texted Dispatch of our intentions. We were below max landing weight and the landing distances looked fine for a trailing edge flap up landing. The passengers were kept informed and the flight attendants did a great job preparing for landing. We encountered some bumps on the approach and the asymmetry decrease requiring less trim. It was a smooth landing with normal breaking and the Fire Chief said the brakes were not excessively hot. We were told to park in the hanger area and I looked at the flap which appeared to be nearly up. I made a log entry that the flap had not retracted on takeoff. On the bus to the terminal I realized that I had not written up the inadvertent overspeed; so I called Maintenance and informed them.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.