Under what conditions can thrust reversers be deployed?

Under what conditions can thrust reversers be deployed?

• A. The radio altimeter reads less than 10 ft RA
• B. The air-ground safety sensor is in ground mode
• C. The radio altimeter reads less than 10 ft RA or the air-ground safety sensor is in the ground mode
• D. Only after engine shutdown

Answer: (C)

Thrust reversers are designed to be usable only when the aircraft is on or very close to the ground, to avoid deploying them during flight. The system gates deployment using two cues: the radio altimeter and the air-ground safety sensor. If the radio altimeter shows you are less than about 10 feet above the ground, you’re in the landing/rollout window and reversers can be deployed. If the air-ground safety sensor indicates ground mode, meaning the aircraft is on the ground (often via gear/weight-on-wheels signals), reversers are allowed to deploy as well. Because either condition suffices, deployment is permitted under the combined rule: less than 10 ft RA or ground mode. Choosing only the radio altitude condition would miss cases where ground mode is detected without RA being below 10 feet, and choosing only the ground sensor would miss scenarios where altitude cues confirm proximity to the ground. Deploying thrust reversers after engine shutdown is not how they’re used; they’re for use during landing rollout, not after shutdown.

Thrust reversers are designed to be usable only when the aircraft is on or very close to the ground, to avoid deploying them during flight. The system gates deployment using two cues: the radio altimeter and the air-ground safety sensor. If the radio altimeter shows you are less than about 10 feet above the ground, you’re in the landing/rollout window and reversers can be deployed. If the air-ground safety sensor indicates ground mode, meaning the aircraft is on the ground (often via gear/weight-on-wheels signals), reversers are allowed to deploy as well. Because either condition suffices, deployment is permitted under the combined rule: less than 10 ft RA or ground mode.

Choosing only the radio altitude condition would miss cases where ground mode is detected without RA being below 10 feet, and choosing only the ground sensor would miss scenarios where altitude cues confirm proximity to the ground. Deploying thrust reversers after engine shutdown is not how they’re used; they’re for use during landing rollout, not after shutdown.