Which airspace requires a coded transponder with altitude reporting for operations above 10,000 feet MSL?

The requirement for a coded transponder with altitude reporting, often referred to as a Mode C transponder, is crucial for maintaining safety and situational awareness in the airspace. The correct choice indicates that all airspace within the 48 contiguous U.S. at and above 10,000 feet MSL requires this specific transponder.

This requirement ensures that air traffic control can accurately identify aircraft positions, their altitudes, and help prevent potential collisions. This altitude threshold is significant as it is where air traffic becomes denser and more complex, typically involving commercial operations and higher traffic density.

In contrast, the other options specify conditions that do not align with the established regulations. For instance, stating that only Class B airspace has this requirement suggests a misunderstanding, as transponder use is not limited to just Class B airspace but applies more broadly. Similarly, indicating all airspace above 2,500 feet or claiming no airspace requires it does not accurately reflect the necessity for altitude reporting in higher altitudes critical for safety in busy air corridors. The regulation is comprehensive as it encompasses greater altitude operations above 10,000 feet MSL across the contiguous United States, reinforcing the importance of maintaining safety protocols for all flights in that airspace.