STAR or IAP?

[Jonai Chui]

I have a question on approaching to major airports which have STARs.
STAR is for large airplanes and IAPs for smaller airplanes, is my understand.
(Even though IAP is only IFR option at smaller airports.)

But there seems to be no definition when pilots should use STAR or IAP.
And all STARs I found ends with "Expect radar vector to the final approach".
If pilots selects STAR, shouldn't they expect IAP? Or are there some STAR which connects to IAP?

Then may large airplane pilots ask IAP instead of STAR?

[OhNoCB]

STARs and IAPs have nothing to do with aircraft type (with the exception that you may get variations within an approach for different aircraft categories which basically accounts for speed ).

STARs are basically a predefined route for aircraft to get towards the initial part of the IAP.

The IAP is the actual approach procedure for aircraft to line up with and descend towards the runway.