How do you distinguish between LOC with NO GS and LOC with unreliable GS?

Distinguishing between Loss of Control (LOC) with No Glide Slope (GS) and LOC with unreliable GS primarily revolves around the aircraft's approach modes and how they are configured on the Flight Control Panel (FCP).

When dealing with No Glide Slope approaches, the aircraft will utilize the APPR (Approach) Mode on the FCP. This mode is specifically designed to handle situations where the glide slope component of the Instrument Landing System (ILS) is not functioning or available. In this scenario, pilots will buy into a lateral-only approach and manage their descent manually or with vertical speed commands.

On the other hand, an unreliable glide slope situation implies that while the system is providing some lateral guidance, the vertical guidance is suspect or has potential inaccuracies. In this case, the system will typically be in NAV Mode, indicating a reliance on navigation signals rather than on a stable, accurate glide slope for descent.

Understanding these distinctions is crucial for pilots to ensure safe approach strategies and decision-making during low visibility conditions. The unique use of APPR Mode for NO GS directly ties into how the aircraft is being guided during the approach, differentiating it clearly from situations where the glide slope is unreliable.