This accident was not subject to an on scene investigation. CIRCUMSTANCES: During a maintenance inspection substantial damage was found to the wing structure in the vicinity of the left main landing gear. It was considered that the damage was consistent with a heavy landing. The aircraft had been flown on several occasions in the previous month by different pilots. No reports had been made of any occurrence likely to cause the damage found to the aircraft. The damage should have been readily noticeable during pre-flight inspections.