This issue (overweight CHC 139's) was discovered about 6 years ago. It wasn't the whole CHC 139 fleet in Australia as someone has suggested, but just 2 aircraft in Karratha (the only ones on contract) in the offshore role. Weight and balance was calculated in good faith before each flight, with operations planned within PC1 limits, and the aircraft were never knowingly operated overweight. This went on for nearly 2 years from memory. Two new aircraft then arrived on contract and the RFM empty weight of both was around 200 kg heavier than each of the "old" aircraft, for no apparent reason. The original aircraft were then re-weighed, and subsequently found to be approx. 200kg heavier than the aircraft empty weight recorded in their respective RFM's. Nothing to do with incorrect sums or equipment not being counted, so no matter how diligent you might be in checking your paperwork before flight you would not have detected the error. I don't recall exactly how the original incorrect empty weights in the W & B section of the RFM occurred, but I believe they were there when CHC Oz took delivery.