When are the probes automatically heated?

• A. Only on the ground
• B. When one engine is started and its generator comes on line.
• C. Only in flight
• D. When the landing lights are on

Answer: (B)

Probes are equipped with heaters to prevent icing from distorting air data readings. These heaters are powered by the aircraft’s electrical system, so they come on automatically as soon as there is electrical power available from the engines. In practice, that means when one engine is started and its generator comes online, the heater circuits for the probes are energized and stay on as long as power is available. The other options don’t fit because probe heating isn’t tied to being on the ground only, being in flight only, or to unrelated things like landing lights; it’s driven by the presence of engine-generated electrical power.