What should a pilot do if the glide slope warning flag appears immediately after passing the final approach fix during an ILS approach?

When the glide slope warning flag appears after passing the final approach fix during an ILS approach, it indicates that the glide slope signal is lost. However, the localizer signal may still be valid, which means the aircraft can still descend using the localizer minimum descent altitude (MDA).

Continuing the approach and descending to the localizer MDA allows the pilot to maintain visual reference and control of the aircraft while being guided laterally by the localizer. Pilots rely on the lateral guidance from the localizer to align with the runway, even when vertical guidance is compromised. It is important to monitor the approach closely, maintain situational awareness, and prepare for a possible go-around if visual references are not established by the time the MDA is reached.

Thus, this response enables the pilot to complete the approach safely while considering the loss of glide slope information.