Whilst descending through about 500ft on final approach to Gatwick, the forward fore flap section from the left hand inboard trailing edge flap assembly came away and impacted the aircraft’s rear left fuselage behind door 4L. The approach was continued and the aircraft landed safely. The aircraft was operating a scheduled service (GA976) from Jakarta via Abu Dhabi and Zurich. On departure from Zurich, with 10deg. flap selected, shortly after take-off and before climb power had been set, the crew felt a slight vibration which lasted about 2 to 3sec. At this time a number of passengers in the rear cabin noticed small pieces of material coming away from the outboard end of the left inboard trailing edge flap and these observations were relayed to the captain. Some time later, the flight engineer came back into the cabin to inspect the area, however, at this stage the flap was fully retracted and no damage was evident. The flight continued uneventfully and on arrival at Gatwick the normal flap lowering schedule was commenced with the flap initially being selected to 25deg. At about 1,300ft. amsl the flap selector was moved to the 30 degree position but the flap remained at 25 degrees and ‘FLAP LD RELIEF’ amber caption came on. (The 30deg flap limiting speed is 180kt. and the aircraft’s airspeed was about 180kt. when the flap selection was made). At about 800ft amsl, with the airspeed now decreased below 180kt., the caption went out and the flaps moved to 30deg. Indications on the flight deck of flap movement were normal, however, shortly after the flap position indicator reached 30deg., the crew felt a moderate vibration and heard a loud bang as the fore flap came away and struck the fuselage. Lateral control appeared to become less positive and there was a tendency to bank left; no pitch control problems were experienced. There were no abnormal indications on the flight deck. The captain decided to allow the co-pilot, who was handling the aircraft, to continue the approach and the aircraft landed safely. The subsequent investigation discovered that the outboard sequence carriage attachment fitting of the left inboard trailing edge flap had been fitted without the required shim under its horizontal attachment flange and with bolts through the flange which were at least one size too long. This resulted in the joint having less than the required clamping force. After some time in service, movement of the attachment fitting relative to the fore flap under flight loads resulted in fretting of the mating surfaces and eventual loosening and release of the five bolts securing the vertical face of the fitting. Fracture of the horizontal flange, weakened by a small area of fatigue, then released the fore flap from the outboard sequence carriage. Subsequent failure of the fore flap near its mid-span and rupture of the two outboard support tracks allowed the outboard section of the fore flap to detach