What is the primary purpose of the outer marker in an ILS approach?

The primary purpose of the outer marker in an Instrument Landing System (ILS) approach is to indicate the initiation of the final approach segment. The outer marker is typically located about 4 to 7 miles from the runway threshold and serves as a critical navigational aid to help pilots confirm that they are on the correct approach path. It signals the pilots that they are at the point where they should begin their final descent to the runway.

This marker is often associated with a specific beacon that activates when the aircraft is in close proximity, providing an auditory and visual signal to the crew. By confirming that they have reached the outer marker, pilots can be assured they are aligned with the approach and can start configuring the aircraft for landing.

While the other choices may seem relevant to different aspects of the ILS approach, they do not capture the specific role that the outer marker plays in the procedure. The descent point is more closely associated with the decision altitude or minimum descent altitude, approach course identification pertains to the entire ILS setup rather than a specific marker, and altitude guidance is provided through other means within the ILS system, like glideslope information.