Can someone tell me how does ATC know when we are established on the localizer and how do they know when to tell us to descend/maintain 3000ft?
The localizer is directly straight out from the runway, so when we see that you are aligned, and are in the center of the red ILS cone, that is how we know you are established, at which point we can hand off to tower.
As for the 3,000 part, I tend to give 3,000 (assuming that the airport is at 0 feet) when turning an aircraft’s base, shortly before the intercept for the ILS approach. That is me though, it’s really controller’s discretion, as long as they are not intercepting you above the glideslope, 3,000 will work any time. It may cut down on their efficiency if it is given any time besides base though, that is the reason most downwinds will be 4,000-5,000, again, assuming the airport is at, or around 0 feet.
Do u mean the triangle shaped thing that extends like 5 miles out of the runway on the map?
Yes. To be clear, it is 10-11 nautical miles long, and the line in the center of that “triangle shaped thing” is the localizer. :)
Haha ok thank you sir :)