When does the amber light on the marker beacon receiver illuminate?

The amber light on the marker beacon receiver illuminates when passing over the middle marker. Marker beacons are used in conjunction with instrument approaches and serve to provide visual indication of a flight's position relative to the runway.

The illumination of the amber light specifically denotes that the aircraft is at the middle marker, which typically indicates that the aircraft is about 3,500 feet from the runway threshold. This provides pilots with situational awareness regarding their distance from the runway, aiding in descent and approach planning.

The other markers, such as the outer marker and inner marker, have their own unique indicators and colors, which differ from the amber light associated with the middle marker. Thus, the amber light’s purpose and timing are explicitly connected to the middle marker's function along the approach path.