In a conventional autopilot system, altitude hold data is provided by which sensor?

• A. Autopilot aneroid
• B. Static port
• C. Pitot tube
• D. GPS altimeter

Answer: (A)

Altitude hold relies on barometric altitude data, which is read by the autopilot from its own pressure-sensing element. In a conventional autopilot, that sensing element is the autopilot aneroid—a sealed, flexible cell that expands or contracts as the ambient static pressure changes with altitude. The autopilot uses the deflection of this aneroid to determine current altitude and to drive the pitch control, keeping the aircraft at the selected altitude.

The static port supplies the raw static pressure to many instruments, including the cockpit altimeter, but the autopilot’s altitude-hold signal specifically comes from the aneroid’s output, which is calibrated to represent altitude. The pitot tube provides dynamic pressure for airspeed and isn’t used for altitude information, and GPS altitude is associated with more modern or navigation-focused systems rather than a conventional altitude-hold loop.