If you inadvertently fly into icing conditions, what should you do first?

Turning on the pitot heat switch is the most immediate action to take if you inadvertently encounter icing conditions. Icing can severely affect an aircraft's performance and control, including blocking the pitot tube, which provides critical airspeed information. By activating the pitot heat, you help prevent ice from forming in the pitot system, ensuring that you can maintain accurate airspeed readings. This is crucial for safe flight, as knowing your airspeed is vital to managing the aircraft's performance during icing conditions.

Other options, while they could be part of a broader response to icing, do not address the immediate need to maintain control of the aircraft. Increasing altitude may help move out of the icing layer, but it should be done with caution and coordination with an understanding of the flight path and aircraft performance. Checking weather reports again is important for awareness, but it cannot replace the urgent need to maintain accurate airspeed information. Performing a controlled descent might be necessary if other conditions worsen, but the first priority should be to ensure that pitot information remains valid to avoid potential loss of control due to unawareness of airspeed.