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It has confirmed that since last August it has bought a vacant section, occupied by a disused tennis court, and two houses.
The vacant property and at least one of the houses is on McBride St, close to the western end of the airport's main runway.
QAC general manager of property and planning Rachel Tregidga said the corporation would not disclose the individual purchase prices "for commercial reasons and to protect the privacy of the vendors".
However, it is understood the vacant section sold for just over $1million and one of the houses fetched about $1.3million.
Asked the reason for the buying, Ms Tregidga stated: "The common element between these purchases is that they sit within the inner noise boundary of the airport, and buying them is a step towards expanding the buffer zone between the airport operations and privately owned residences."
Mountain Scene reported in 2016 that QAC had paid $1.28million for a four-bedroom home on the runway side of McBride St, meaning it owned three adjacent properties on the same street.
At the time, acting QAC chief executive Mark Edghill said QAC intended using the houses to test noise mitigation measures.
QAC offers acoustic insulation to properties within its inner air noise boundary.