Relevant Discussion: 91.215, 91.217, 91.135, 91.411, 91.413, 99.13, 121.345, 135.143, AIM 3-2-3, 3-2-4, 4-1-20, 5-6-4, 6-2-2, 6-4-2, FAA-H-8083-16, 8083-25
Everything You Need to Know about Mode C Transponders
Key Takeaways:
- Transponders with Mode C are broadly required in Class A, B, and C airspace, within 30 nm of certain airports, and at/above 10,000 feet MSL in the contiguous US, with specific exemptions for aircraft without engine-driven electrical systems, balloons, or gliders.
- Mode C transmits pressure altitude (independent of altimeter setting) and must agree with the barometric altimeter within ±125 feet. Pilots use common squawk codes (e.g., 1200 for VFR, 7700 for emergency) and the "Ident" button only when requested by ATC.
- Altitude encoders require testing and recertification every two calendar years for IFR flight in controlled airspace. Specific procedures exist for obtaining authorization to fly with an inoperative transponder or for unequipped aircraft.
Key takeaways sponsored by Aviator Pro | Start Your Training ->
See a mistake? Contact us.
