Full TCAS operation requires an operating transponder on all associated aircraft. Which mode is required?

Full TCAS operation requires an operating transponder on all associated aircraft. Which mode is required?

• A. Mode A
• B. Mode C
• C. Mode S
• D. Mode A and C

Answer: (C)

TCAS relies on cooperative surveillance from nearby aircraft to determine threat levels and generate safe advisories. For TCAS to work reliably, each aircraft being tracked must provide precise data, including altitude and a unique identity, so targets can be distinguished and tracked consistently as they move. Mode S transponders deliver a discrete address and enhanced altitude encoding, giving TCAS clear, unambiguous data about each intruder. This rich data set supports accurate target differentiation, multi-target tracking, and appropriate resolution advisories. Modes that only provide identity (Mode A) or altitude without a unique address (Mode C) can leave targets ambiguous or limit TCAS’ ability to manage multiple aircraft simultaneously. Therefore, to ensure full TCAS operation across all associated aircraft, Mode S is required.

TCAS relies on cooperative surveillance from nearby aircraft to determine threat levels and generate safe advisories. For TCAS to work reliably, each aircraft being tracked must provide precise data, including altitude and a unique identity, so targets can be distinguished and tracked consistently as they move.

Mode S transponders deliver a discrete address and enhanced altitude encoding, giving TCAS clear, unambiguous data about each intruder. This rich data set supports accurate target differentiation, multi-target tracking, and appropriate resolution advisories. Modes that only provide identity (Mode A) or altitude without a unique address (Mode C) can leave targets ambiguous or limit TCAS’ ability to manage multiple aircraft simultaneously.

Therefore, to ensure full TCAS operation across all associated aircraft, Mode S is required.