Leadie you are correct the Sydney Airport Demand Management Act was enacted under the coalition.
This Act involved a lot of trade-offs and no-one got what they wanted. For example Marrickville Town Hall were very opposed to the third runway and if I remember correctly were pushing for a movement cap of something like 55 movements per hour, yet industry was pressing for something like 110. In the end we got 80.
However the deal was done whilst the Keating Government was in power and was a culmination of a well organised and at times bitter campaign by Marrickville Town Hall led by then Mayor Barry Cotter, a number of very influential Labour politicians including Laurie Brereton (Federal Minister for Transport at the time), Andrew Refshauge (Deputy Premier at the time) and many others,
(note that Carmel Tebbutt, Anthony Albanese's wife, was Deputy Mayor of Marrickville during this period, although I don't specifically recall her being one of the voices) over the third runway.
The Sydney Airport Demand Management Act, and the Howard Governments "support" for the Sydney Airport Curfew Act (which was legislated under Keating in 1995), were deals that had been already done and would have been near impossible to undo at the time...
And although the Sydney Airport Demand Management Act was enacted when the coalition were in power, I think it is a bit of a stretch to apportion responsibility to them. This legislation was very much a child of the Labour Party.
Mind you
On this one, no political party can be expected to have the courage to legislate change
sadly you are probably right!