Originally Posted by
chevvron
Similar to an ILS to allow the aircraft to be stabilised on final approach track before commencing descent.
Not really true any more.
One of the problems with implementation of 'RNAV approaches' is that the simple thing for regulators was to overlay them on ILS procedures. Beancounters then asked what are we doing all this extra training for? At which point some airlines ceased equipping for RNAV approaches.
The future is more likely to be curved approaches (sometimes multiply curved approaches) where the aircraft is 'established' once it starts the procedure regardless of whether the aircraft is flying a straight track on the ground.
See
https://www.faa.gov/nextgen/snapshots/stories/?slide=6
When 4DTBO eventually becomes accepted the trajectory is likely to include 'Greener Skies' type approach paths as part of a continuous descent.