EMB ERJ 145 ER/LR
Confusion
Aircraft Equipment Problem Critical; Inflight Event / Encounter Fuel Issue
Flight Crew Returned To Departure Airport; General Maintenance Action; General Declared Emergency; General Flight Cancelled / Delayed
Aircraft
Shortly after takeoff; on initial climbout; the Flight Attendant contacted the flight crew on the emergency interphone to report a possible fuel leak out of the left tank. The Flight Attendant also had video available that passengers were taking with personal smart phones of the event. [We were] continuing to climb due to mountainous terrain on the departure path. An initial scan of the Fuel System did not reveal an obvious leak; fuel imbalance less than 100 LBS. The Flight Attendant offered the video to the Captain (pilot not flying); the Captain accepted. After a brief review the Captain also concluded the aircraft was leaking fuel just outboard of the outer flap panel. The Captain immediately declared an Emergency with Departure; requested ARFF support; and instructed the First Officer (pilot flying) to return to the airport. After leveling off (10;000 FT) the fuel leak stopped. As the fuel leak did not pose a flight controllability issue; the Captain elected to have the First Officer continue as pilot flying; while the Captain undertook the necessary coordination with ATC; Operations (via ACARS) for a safe air return. After landing; the Captain taxiied to a remote parking location; where ZZZ Station Operations were already waiting. [We] powered down the aircraft to remove any ignition sources. Passengers were deplaned after ARFF and the Captain determined the area outside the aircraft was safe. Fuel leak during the most critical phase of flight; leak not visible from the flight deck. A post flight examination by Maintenance personnel revealed a flapper valve was leaking.
Flight Attendant notifies flight crew that fuel was leaking from Left tank shortly after takeoff.  Captain offered video of left wing taken by passenger and concluded fuel leaking just outboard of outer flap panel. Emergency declared and the EMB-145 aircraft returned to field. Maintenance inspection revealed a flapper valve leaking.