What are the three portions of the aircraft that you must avoid at all times?

The three portions of the aircraft that must be avoided at all times during helicopter operations are the main rotor blade, tail rotor blade, and cargo hook. These components pose significant safety hazards due to their motion and function.

The main rotor blade spins rapidly and has a wide radius, which creates a risk of injury or fatality if someone is near it while in operation. The tail rotor blade is similarly dangerous; it counterbalances the torque generated by the main rotor and also spins at high speeds, making it equally perilous for personnel around the aircraft. The cargo hook is crucial for loading and unloading operations but can also cause injury if personnel are in the wrong position during these actions.

In contrast, other options consist of parts that, while part of the aircraft's structure, do not pose the same immediate danger once the aircraft is on the ground or during operation. The emphasis on the specific components in the correct answer highlights their critical nature in safety protocols during air assault and helicopter operations, reinforcing the need for awareness and caution in their vicinity.