What four devices are operated by the primary hydraulic system under normal operations?

The correct answer identifies the four devices that the primary hydraulic system operates under normal conditions, which are the Landing Gear, Landing Gear Inboard Door, Flaps, and Speed Brake.

In conventional aircraft design, the primary hydraulic system is responsible for essential functions that require reliable and robust actuation. The Landing Gear is critical for takeoff and landing phases, and it must operate smoothly and efficiently, which is why it is typically powered by hydraulic systems. Additionally, the Landing Gear Inboard Door, which closes and seals the gear compartment during flight, also relies on hydraulic power for operation.

Flaps are crucial for enhancing lift at lower speeds, thus enabling safer takeoff and landing procedures. Their operation is highly dependent on the hydraulic system, which provides the necessary force to extend and retract them. Lastly, the Speed Brake serves to decrease the aircraft's speed during descent and landing by increasing drag, and it is similarly operated by the primary hydraulic system to ensure swift and reliable performance when needed.

This understanding reflects the typical design priorities in aviation, where the primary hydraulic system supports crucial components involved in safe aircraft operation.