The Skyservice Airlines Boeing 727-231 aircraft, flight SSV857, was conducting an approach to runway 23 at Toronto (CYYZ). While on final approach, the First Officer selected the flaps down to the twenty-five degree (25§) position. A loud bang was heard, originating from the rear of the aircraft and a significant jolt was felt on the Captain’s control column. The aircraft had a noticeable left roll tendency which required right aileron in order to maintain directional control. The flight crew decided to land without lowering more flap and the aircraft landed without further incident. The aircraft was inspected after landing and company maintenance personnel discovered that a 12 foot by 1 foot section of the trailing edge of the left inboard fore flap was missing. Further inspection revealed a large dent in both the intake cowling and engine attachment pylon of engine number one. There were also a number of deep scratches found on the left aft section of the fuselage.