GPWS alerts are triggered by threshold criteria between 50 ft and 240 ft radio altitude. Which of the following is a GPWS threshold in this range?

• A. Excessive descent rate
• B. High engine vibration
• C. Low fuel state
• D. Stall warning

Answer: (A)

GPWS thresholds are tied to how close you are to the terrain, using radio altitude to decide when to warn. In the final approach heights—roughly the 50 to 240 feet radio altitude window—the system most commonly triggers when the aircraft is descending too quickly, a condition known as an excessive descent rate or sink rate. This warning is specifically designed to catch a situation where you’re too close to the ground and still descending steeply, signaling you to pull up to avoid a terrain impact.

The other possibilities don’t come from the GPWS thresholds used in this low-altitude band. High engine vibration relates to engine health, not proximity to the ground. Low fuel state is a fuel quantity issue, not a terrain alert. A stall warning is about angle of attack and aerodynamic stall, not how close you are to the terrain.