No certificate holder may move an airplane when which of the following is present at a passenger seat?

The correct answer is that no certificate holder may move an airplane when food is present at a passenger seat. This regulation is in place to ensure safety and compliance with operational protocols. The presence of food at a passenger seat can pose a risk during taxi, takeoff, or landing phases of flight. It is important to maintain a clear and organized cabin environment to ensure that all passengers are properly seated and secured in case of unexpected events.

In addition, food can become a projectile if there is sudden movement, which can cause injury to passengers or crew. Therefore, airlines typically have strict policies regarding the placement of food during certain phases of flight to prevent hazards and maintain order within the cabin.

The other options, while also concerning safety and organization, do not carry the same level of urgency that would necessitate a restriction on moving the aircraft. Emergency equipment is essential for safety, passenger luggage is typically secured according to regulations, and flight manuals are necessary for operation but are not likely to impede safety when present.