What must the cockpit door be during the use of electric heat?

The correct answer is that the cockpit door must be open during the use of electric heat. This requirement is in place to ensure proper ventilation and prevent the buildup of potentially harmful gases or fumes within the cockpit. Electric heating systems introduce additional heat into the cockpit environment, and without adequate ventilation, there could be a risk of carbon monoxide or other hazardous gases accumulating, especially if there is a malfunction.

Keeping the cockpit door open allows for the circulation of air, ensuring that the occupants are not exposed to harmful conditions. It also helps to maintain a comfortable and safe operating environment while the electric heat is in use. The importance of air circulation is critical for safety, which is why this regulation is strictly enforced in operations involving electric heating.