EDIT: I assumed it was coming from the north. Coming in from AKL, the WAREN7A looks like the STAR they did. The final segment before AKDEL on that arrival is also 2500ft, so the same still applies. They were at 2400ft before the turn.
The answer to this question will help with the use of a diagram. Coming in from the north, there’s essentially a series of “steps” that includes the minimum altitude on each leg.
In the first picture the lowest altitude an aircraft can be there is 2500ft which goes all the way to the waypoint AKDEL.
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In the second picture from waypoint AKDEL, the next step stops at 1500ft. So if we think about a helicopter for a second, we fly to waypoint AKDEL at 2500ft and then the second we pass it we drop to 1500ft. In an aircraft though we obviously can’t do this and it’s also not very economical. So we try to fly a constant descent if we can.
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The coding in the flight management computer will code the aeroplane at AKDEL to 2500ft and then fly level for about 2.5nm to intercept the glide path for 34. This also uneconomical. So I code the FMC to be at AKDEL at 3000ft and during the turn, I’ll start configuring and it’ll be a constant descent all the way.
Now, practically, the turn itself would be quite sharp to fly all the way to AKDEL and then start the turn. It would also mean that we would overshoot the final approach path. Not so much of a problem in Melbourne but it is at airports with parallel runways. So instead the aircraft bypasses the waypoint to make a nice smoother transition to final.
In regards to Garuda though, (and I’d have to check the FR24 track to see) to be at 1700ft by the end of that turn means that they would have been lower than 2500ft before reaching AKDEL. It’s a common trait I see with overseas airlines that they see the steps as a target altitude rather than a limit. At 1700ft they would intercept the final approach path at BOSGI (4nm from the runway).
Sorry it’s a bit of a longer answer, I turn into a pumpkin at midnight tonight, as my cyclic currency runs out and there’s no plan to get me current in the next roster, so I’ve got a bit of time on my hands.