What altitude reporting capability is required for the transponder within Class B airspace?

What altitude reporting capability is required for the transponder within Class B airspace?

• A. Mode A with no altitude reporting
• B. Mode C automatic altitude reporting
• C. Mode S with altitude reporting
• D. Mode C altitude reporting only

Answer: (B)

In Class B airspace, ATC needs reliable altitude data from every aircraft to separate traffic on radar. The required capability is automatic altitude reporting, which is provided by a transponder operating in Mode C. This encodes and sends your altitude to ATC when interrogated, giving controllers the vertical position of your aircraft. Most aircraft use a combined Mode A/C transponder, which handles both the discrete identity code (Mode A) and altitude reporting (Mode C). The other options aren’t the standard requirement: Mode A only has no altitude data; Mode S can report altitude but isn’t the baseline requirement for Class B; and saying “Mode C altitude reporting only” would omit the identity code that is also part of typical Class B transponder operation.

In Class B airspace, ATC needs reliable altitude data from every aircraft to separate traffic on radar. The required capability is automatic altitude reporting, which is provided by a transponder operating in Mode C. This encodes and sends your altitude to ATC when interrogated, giving controllers the vertical position of your aircraft.

Most aircraft use a combined Mode A/C transponder, which handles both the discrete identity code (Mode A) and altitude reporting (Mode C). The other options aren’t the standard requirement: Mode A only has no altitude data; Mode S can report altitude but isn’t the baseline requirement for Class B; and saying “Mode C altitude reporting only” would omit the identity code that is also part of typical Class B transponder operation.