In Class B airspace, under which conditions is Mode C transponder required?

In Class B airspace, a Mode C transponder is required under specific conditions to maintain situational awareness and ensure safety among the higher density of air traffic usually present in those areas. When flying within 30 nautical miles of a primary Class B airport and below 10,000 feet Mean Sea Level (MSL), the transponder plays a critical role in providing air traffic controllers with the necessary information about aircraft location, altitude, and speed.

This requirement is particularly critical because Class B airspace is designed to contain all the traffic patterns associated with busy airports. By having a Mode C transponder activated, aircraft are able to be tracked effectively, which minimizes the risk of mid-air collisions and enhances overall traffic management.

The other scenarios listed do not fully encapsulate the specific operational needs associated with the safe navigation and coordination in Class B airspace. For instance, while a Mode C transponder is essential for certain contexts, the requirement for all times regardless of altitude (as in the first choice) does not accurately represent the nuanced operational regulations specific to different altitudes and airspace. Additionally, the requirement below 2,500 feet AGL only, and above 10,000 feet MSL in all airspaces, do not specifically address the safety