Define "controlled descent area" (CDA).

The definition of a "controlled descent area" (CDA) aligns with the concept of managing a flight's descent profile to achieve multiple operational benefits, specifically minimizing noise and improving fuel efficiency. This practice involves defining a specific path for aircraft to follow when descending, often characterized by smooth and gradual descents rather than a series of abrupt changes.

By implementing a CDA, pilots can reduce engine power settings during descent, which not only lowers fuel consumption but also decreases the noise produced by the aircraft, particularly when flying over populated areas. This is especially significant in aviation operations around densely populated airports where noise abatement procedures are critical.

Other options do not accurately capture the meaning of a controlled descent area. For instance, altitude restrictions at busy airports pertain more to traffic management than to the efficient descent profile sought in a CDA. Similarly, zones for emergency landings and methods for takeoff do not relate to the specific control of descent paths and their associated benefits. Thus, option A effectively encapsulates the core objectives of a controlled descent area in modern aviation practices.