Which of the following thresholds is used in GLD Auto Deployment criteria involving the radio altimeter?

• A. Radio Altimeter -7 Feet
• B. Radio Altimeter +7 Feet
• C. Radio Altimeter -15 Feet
• D. Radio Altimeter -0 Feet

Answer: (A)

GLD Auto Deployment uses the radio altimeter to sense how close the airplane is to the runway and to time the deployment of the ground lift devices accordingly. The idea is to trigger deployment very close to touchdown so that the wings’ lift is dumped right as the aircraft sits on the wheels, maximizing braking effectiveness without deploying too early in the flare or while still in the air.

The threshold in this system is set at seven feet, using the radio altitude reading as the trigger point. When the radio altitude reaches about seven feet, and other conditions (like weight on wheels) are satisfied, the GLD can automatically deploy. The negative sign in the value is simply the system’s convention for expressing this near-ground proximity; it doesn’t imply being below ground. What matters is that the aircraft is within a small distance of the surface, allowing timely and safe GLD deployment.