Which of the following is NOT a mode of GPWS?

The correct answer is that flight path deviation is not a mode of Ground Proximity Warning System (GPWS). GPWS is designed to provide alerts to pilots when the aircraft is in a potentially hazardous situation concerning terrain or obstacles. The primary modes of GPWS include:

1. Excessive Rate of Descent (ROD) - This mode alerts pilots if the aircraft is descending too rapidly, which could lead to a controlled flight into terrain.

2. Gear and Flap Not Selected - This mode provides warnings when the aircraft is below a certain altitude and the landing gear or flaps are not configured for landing, indicating a potential conflict with the terrain.

3. Windshear - This mode warns pilots about wind shear, which can cause sudden changes in altitude or airspeed, potentially leading to hazardous flying conditions.

Flight path deviation, while important for overall situational awareness and safety, does not constitute a specific mode in GPWS. It refers to the aircraft's actual versus intended flight path, rather than a direct alert condition under which GPWS activates. Thus, the absence of flight path deviation as a defined mode makes it the correct choice for this question.