What is the primary function of the transponder in a commercial aircraft?

The primary function of the transponder in a commercial aircraft is to provide identification and altitude information to Air Traffic Control (ATC). When an aircraft's transponder is activated, it sends a signal that includes the aircraft's unique identification code, as well as its current altitude. This information is vital for ATC to maintain safe separation between aircraft and to manage air traffic effectively.

The transponder enhances situational awareness for both pilots and controllers, allowing them to identify and track aircraft on radar displays. This capability is especially essential in busy airspace, where multiple aircraft are operating simultaneously. The transponder's data allows ATC to monitor traffic, direct aircraft during takeoff and landing, and manage flight paths safely.

The other options focus on functions not associated with a transponder's primary role during flight operations. Direct communication with the pilot, managing ground operations, or detecting enemy aircraft are not functions related to the transponder, which is specifically designed to assist in identification and altitude reporting for safe airspace management.