Which system is crucial for notifying pilots of altitude deviations?

Answer: B — Altitude Alerting system

The Altitude Alerting System is crucial for notifying pilots of altitude deviations because it actively monitors the aircraft's altitude relative to the selected flight level. When the aircraft deviates from the preset altitude—either climbing above or descending below the chosen level—this system generates alerts, typically through visual or auditory signals in the cockpit. This early warning allows pilots to take corrective action, ensuring safer flight operations and maintaining altitude adherence, which is essential for avoiding conflicts with other aircraft and for compliance with air traffic control clearances. In contrast, other systems serve different purposes. The Traffic Collision Avoidance System focuses on preventing mid-air collisions by advising pilots of potential traffic conflicts. Automatic Dependent Surveillance provides situational awareness and is used for tracking and reporting aircraft position, but it does not specifically alert pilots about altitude deviations. The Ground Proximity Warning System is designed to prevent controlled flight into terrain by alerting pilots when the aircraft is too close to the ground without proper clearance, rather than monitoring altitude maintenance during a flight.