What mode in GPWS alerts flight crew to insufficient terrain clearance when not in the landing configuration?

The correct answer is attributed to Mode 4 of the Ground Proximity Warning System (GPWS). Mode 4 is specifically designed to alert flight crews when the aircraft is not in the landing configuration but is dangerously close to terrain, indicating insufficient terrain clearance. This is particularly relevant during phases of flight where the pilot may not expect to be at a low altitude, such as during a climb or cruise, rather than on approach for landing.

In Mode 4, the system uses altitude and geographic data to detect potential conflicts with terrain, thereby prompting alerts that allow pilots to take corrective action to prevent an unintentional terrain impact. Understanding the specific functions and capabilities of each GPWS mode is critical for flight crews to ensure safe operation and to respond effectively to alerts.

The other modes are designed for different scenarios, such as detecting excessive descents or capturing the approach profile, and do not specifically address the need for terrain clearance when the aircraft is in a non-landing phase.