B757 Captain is informed by a Flight Attendant that pieces of a leading edge slat are departing the aircraft. After consulting with Maintenance; crew elects to declare an emergency and return to departure airport.

Narrative

During climb after FL180 the aft Flight Attendant called and said a passenger in a window seat noticed part of the left wing peeling off. She said he was an FAA Inspector and he said he saw chunks of metal flying off of the wing. We asked for passenger's credentials and Flight Attendant brought them to cockpit for us to verify. Then First Office proceeded to the back of the aircraft to inspect the damage. He saw a large hole in the top of the wing and pieces of honeycomb were still flying out of it. He returned to the cockpit to inform the Captain. We checked stability of aircraft by disengaging the autopilot and aircraft responded normally. By this time we were at cruise and we contacted Dispatch who connected us to Maintenance. Maintenance looked over aircraft history and said the #5 slat had undergone an interim repair a few months earlier and that it was probably the bindings coming off from the earlier repair. By this time many passengers had also noticed the debris flying off the leading edge of the wing. We elected to declare an emergency with ATC and we asked Dispatch for the weather as well as performance/landing data and declared our intentions to them about returning. After declaring an emergency and stating our intentions to return; Air Traffic gave us vectors to avoid some weather and then cleared us for the arrival. We configured the aircraft early to make sure there would be no slat/flap configuration problems and had emergency equipment standing by. We landed uneventfully and reported and wrote up our overweight landing.