What must a pilot do upon encountering a glide slope warning flag during the final approach?

When a pilot encounters a glide slope warning flag during the final approach, it indicates a problem with the glide slope signal, meaning the aircraft may not achieve the optimal descent path for landing. The appropriate action under these circumstances is to revert to the standard Minimum Descent Altitude (MDA).

Maintaining the standard MDA ensures that the pilot is safely above any potential obstructions and can continue the approach while assessing the situation further. This approach allows the pilot to either attempt to regain the glide slope, if possible, or prepare for a missed approach. It emphasizes safety by avoiding descent below the minimum safe altitude without confirmed visual reference for landing.

In contrast, calling for assistance, maintaining the current altitude, or continuing to land despite the warning would not adequately address the potential hazards presented by a lost glide slope signal, making reverting to the standard MDA the safest and most prudent choice.